Transcript for:
Understanding Intermolecular Forces in Chemistry

welcome back everyone this is AP Chemistry Chrome study for unit 3. in unit 3 we will learn intermolecular forces and properties we're going to deal with hydrogen bonding um dipole-dipole Force um the London dispersion force will also learn ideal gas flow and deviation from the ideal gases we'll also deal with the spectroscopy and the Beer's Law let's get started first off we will start with intermolecular force so by the name suggests inter means on between so intramolecular force literally means it is the forest order attraction between the molecules in this chapter we will deal with intermolecular force in between the same molecules and intermolecular forces between different molecules well when we study the intermolecular first between the same molecules or the molecules with the same species it's used to explain the physical property of this substance such as the melting point such as the boiling point such as the viscosity well let's say oil a lot of vegetable oils are very viscous more viscous than water we will use the intermolecular first in between the oil and then we can explain the high viscosity of oil and let's say oil does not dissolve in water they are not soluble to each other well that we can use the intermolecular force in between these two different molecules to explain it on the other hand sodium chloride the table salt is pretty much soluble in water we can use intermolecular first between the ionic compounds and water molecules to explain it here are couples of different types of intermolecular forces from the wickest to the strongest they are London dispersion force which occurs between non-polar molecules or noble gas remember that noble gas exists in the form of one single atom so they are not molecules there are atoms the next book is dipole and dipole interaction so dipole dipole Interruption occurs between the polar molecules and next will be hydrogen bonding it's a special type of Double-Double interaction so it occurs within a highly polar molecules and these molecules must contain the highly electronegative atoms nitrogen oxygen and fluorine and the next the strongest one occurs between ion and polar molecules and it's called ion dipole Force well we'll dive deep into every single type of the first intermolecular force we're going to dive into is a linear dispersion force as I stated before learning dispersion force occurs within nonpolar molecules and Noble guess okay so Noble guess um exists in the form of one single atom that's why we don't call them molecules um well then some people might ask how come there is an attraction force between the non-polar molecules because they're basically neutral and they are nonpolar it is because non-polar molecules can still form dipole that what is a dipole so the molecule as a whole it is neutral what I mean by that is the electrons are distributed evenly within the molecules and electrons are shared equally between two ends of that two ends of the molecules but at a certain point because electrons are mobile electrons might be more concentrated on the right side of this on the right end of this molecule and then there are only very few electrons Left To the Left End of the molecule then the right end of the molecule carries a partial negative charge and then the Left End carries a partial positive charge this is what I call by the dipole so dipole is basically the separation of charges within a molecule because this is non-polar molecule and in general they only form temporary dipole what I mean by temporary is electrons are concentrated more on one end temporarily as long as this temporary dipole occurs it's going to induce another molecule right next to it to form another dipole because light charges repel online charges attract so a lot of electrons on the right end of this molecule will push the electrons away from the left end of this molecule so electrons are pushed toward the Right End very few electrons are left on the Left End so again for this molecule it's induced to carry its induced to have the separation of charges again the Right End carries a partial negative charge the Left End carries a partial positive charge and this induced dipole will induce another molecule right next to it to become induced dipole and we call them dipole induced dipole another dipole induced dipole electrons are pushed toward the right end so the Right End carries partial negative charge left and Carries partial positive charge again light charts repel online charges attract so in between two opposite ends of the molecules they are going to form this attractive Force which is what we call by London dispersion force different molecules different substance just has different amount or different size of the London dispersion force and the size of the London dispersion force depends on two factors one is polarizability the the second one is the contact area polarized ability is a tendency of a molecule to form the dipole moment and usually polarizability depends on the molecule size and the number of the electrons this is because the more electrons a molecule has then more likely that electrons are dispersed not tightly bonded to the nucleus let's say a thousand dollars in total the wealth Gap can be 999 dollars and then one dollars right if another country has ten thousand dollars then the wall scap can be more extreme because you can separate ten thousand dollars into one dollars and 999. so the wall scam is bigger in in this in this country because it just has more of the money to distribute between two ends so that's exactly the same when you have more of the electrons then the distribution of the elect electrons within the molecule can be more extreme or more unbalanced so any molecule that has more electrons will be more polarizable here are a couple of examples I can compare the linear dispersion force within ccl4 and CH4 chlorine and chlorine is how so it has seven valence electrons while hydrogen carries only one valence electrons as for the size this one is a little bit bigger than the methane but not that much difference but what really makes a difference is the number of the electrons because ccl4 has more electrons so it has higher polarizability so ccl4 has a greater London dispersion force compared to the methane CH4 another example will be the c2h6 ethane versus butane c4h10 both are hydrocarbon chain with single Bond only but in ethane we have only two carbons in six of the hydrogens while in butane I have four carbons and 10 hydrogen so a larger molecule size means that more electrons this means the butane c4h10 has a greater polarizability so in conclusion the c4h10 will have a greater London dispersion force and then the second factor that affects the London dispersion force will be the contact area greater the contact area than greater the London dispersion force let's compare isobutane and butane both isobutane and butane has the chemical formula of c4h10 they have exactly the same chemical formula but they have different three-dimensional structures butane is a linear shape while isobutane has three carbons bonding to each other in a linear shape and then the first carbon attached to the central carbon so it has a more rounded shape so even though they have exactly the same chemical formula which means the molecule size is the same and in the same number of the electrons but butane will have a greater lunar dispersion force compared to isobutane when they're in contact with each other their contact areas area is much greater the butane molecule stuck up closely to each other so the contact area is pretty big they are in contact with this much of the area on the other hand for the isobutane they have more rounded shape like circles so when they're in contact with each other they're in contact only at very small surface area so imagine that you have a very sticky very strong sticky glue when you're trying to stick two balls together because they're in contact with each other at very small surface so it's very likely that they will just fall off easily but if you're trying to put two pieces of papers together if you're in contact with the whole surface the papers will get sticked to each other better this is why the greater contact area means greater London dispersion force so in general London dispersion force is usually considered to be very weak it is the weakest and among all of the intermolecular forces but if the molecule size get very very big um such as a very long hydrocarbon chain then the London dispersion force will get very big because of the large contact area the next is dipodipo interaction dipole dapple interaction occurs within the polar molecules because the bond is polar it is a permanent dipole you will observe this attraction force between the opposite ends of the molecule because learning dispersion force occurs between temporary dipole at a very specific point um the temporary Temple might just go back to the regular nonpolar molecules and the dipole moment disappears then there will be no force in between those molecules so learning dispersion force is weaker for the polar molecules the dipoles are there all the time like permanently so usually it's stronger than the London dispersion force so one thing to remember is that for any polar molecules it has they have a both dipole dipole interaction and London dispersion force so it's impossible for any of the polar molecules to have dipole dipole only if they have dipole Depot interactions then they must have learned a distribution Force so London dispersion force is a prerequisite for the dipole dipole interaction and here are a couple of examples of the polar molecules that have dipole Depo interactions between the molecules hydrochloric acid HCL so hydrogen and chlorine well hydrogen carries the hydrogen and carries a partial positive charge and then the chlorine and carries a partial negative charge so when you have these molecules they will align So within the sample of the hydrochloric acid that will just automatically align in a way that um the the partial negative ends and then the partial positive ends are right next to each other and then the dipole dipole interaction forms between the opposite ends another example will be formaldehyde ch2o oxygen is highly electronegative so the oxygen n carries a partial negative charge and then the hydrogen end carries a partial positive the positive and a negative end they will be attracted to each other to form this dipole-dipole interaction which is stronger than London dispersion force the next will be hydrogen bonding so hydrogen bonding is the strongest out of the three intermolecular forces hydrogen bonding is actually a special type of dependental interaction so it also occurs within a polar molecules but this polar molecules must include um hydrogen bonded to a highly electronegative atoms nitrogen oxygen or fluorine water is one of the most common example of hydrogen bonding so water H2O two of the hydrogen atoms are bonded to one oxygen atoms and the oxygen and carries a partial negative charge and the hydrogen ions carry a partial positive charge and again that will naturally align in a way so that the hydrogen ends are right next to the oxygen and of another molecule and this is what I refer to as hydrogen bonding okay again for these type of molecules they have London desperation Force they have dipole-dipole interactions and then they have hydrogen bonding so it's impossible for these molecules to have only hydrogen bonding or only hydrogen bonding and typo dipole or only hydrogen bonding and little dispersion force if any molecule had hydrogen bonding that it must have the other two as well another example for hydrogen bonding is ammonia NH3 so nitrogen is the central atom and then it is bonded to three hydrogen atoms by single bonds it has a lone pair electron on the nitrogen so again because nitrogen is highly electric electronegative um atom so the nitrogen and Carries partial negative charge the hydrogen n carries partial positive charge and the hydrogen end of one molecule will be aligned right next to the nitrogen end of another molecule in this attraction between the opposite ends um is hydrogen bonding when it comes to hydrogen bonding we really need to pay attention to um how the hydrogen how the hydrogen atom is bonded within the molecule what a lot of people make mistake is they just seeded this molecule has hydrogen and oxygen or hydrogen and nitrogen and then they immediately think this this molecule has hydrogen bonding this is not true so for example formaldehyde in the last and the last couple of pages ch2o so carbon is bonded to two hydrogen atoms by single Bond and then it's also bonded to Oxygen by a single Bond okay so even though this is a polar molecule it does not form the hydrogen bonding okay this is because the hydrogen is not bonding to highly electronegative atom oxygen okay why does that matter um it is because hydrogen carries partial positive charge only when it's bonding to the highly electronegative atom because highly electronegative atom means that it's going to drags or pull the electrons um toward more toward herself so when a hydrogen is bonding to oxygen or hydrogen is bonding to a nitrogen more of the electron cloud is around around oxygen and not around the hydrogen but the hydrogen carbon bond is pretty much nonpolar so hydrogen and carbon they they share the electrons equally so this hydrogen it does not carry any of the positive partial or positive charge so even though the oxygen carries a little bit of partial negative charge we do not find a partial positive charge on the hydrogen so that's why so that's why it's not going to form the hydrogen bonding um just like water or ammonia the next is the iron type of force which is the strongest out of the four intermolecular forces that we learned in AP Chemistry the other three London dispersion force dipole-dipole interactions and hydrogen bonding all describes the intermolecular force between the molecules molecules and molecules as well on the other hand ion dipofores describes the intermolecular first between ion and the molecules it's especially useful when it comes to explaining the solubility of ionic compounds in water so most common ionic compounds such as sodium chloride when it dissolves in water then it dissociates from sodium chloride in solid to sodium plus cations and then chlorate minus anions and this is pretty much explained by the iodiper force between the cations anions and the water molecules so sodium cationine care is partial it carries the positive charge so sodium cations carries the positive charge and water molecules are permanent dipoles which means the partial negative side the partial negative end of the water molecule the oxygen n will be attracted toward the sodium cations so sodium cations are surrounded by water molecules with oxygen facing towards the sodium on the other hand the chloride anion which carries the negative charge will be attracted toward the positive end of the water molecule which is the hydrogen and it applies to all of the ionic compounds such as sodium bromide zinc chloride Etc the crystal structure of sodium bromide is represented in the diagram above that is a highly ordered Crystal letter structure so obviously this represents a solid which demon correctly compares the crystalline sodium bromide in solid to the molten sodium bromide liquid in terms of electrical conductivity a crystalline sodium bromide contains no freely moving electrons that could okay this part is correct that could connect electrical current whereas electrons can flow freely in the molten sodium bromide okay the second part is not true so the molten sodium bromide does not have freely moving electrons um it's just that the sodium cations and bromide anions are free to move so it's the ions which are free to move in the liquid state so a is not true B cursed only sodium bromide and molten sodium bromide both contain ions that are held in a fixed position this is not true because the molten sodium bromide um in in the in the liquid state the mult the molten um in the liquid state the sodium cations and bromic anions are free to move so B is not correct C crystalline sodium bromide and molten sodium bromide both contain sodium atoms this is not atoms it's cations so not true D okay that's the right answer crystalline sodium bromide contains no freely moving electrons to connect electricity but molten sodium bromide is composed of freely moving sodium and bromide ions which allows it to be a good conductor which is true the next which particle diagram is shown above that represent the strongest intermolecular force between two ethanol molecules for diagram one it can consists of carbon hydrogen and oxygen um so the intermolecular force occurs between the hydrogen of two of the molecules okay so the carbon and hydrogen bond it is non-polar bond which means this part it's non-polar okay so it will be the London dispersion force for the diagram one in diagram two um it's still the same molecule with carbon hydrogen and oxygen but now this time the intermolecular force occurs between the oxygen and the hydrogen and in the second molecule this hydrogen is bonded to oxygen which is highly electronegative atom which means the electron cloud are dragged toward oxygen and then hydrogen is deprived of electron clouds which makes it carry a partial positive charge and oxygen obviously carries a partial negative charge so um this will be the hydrogen bonding for diagram two so obviously hydrogen bonding is much more stronger than London dispersion force so um A and B are not correct so it's going to be either C or D let's take a look at the reason C because it shows the formation of hydrogen bond between hydrogen atoms bonding to an oxygen and an oxygen atom from another molecule so C is the right answer and D because it shows a dipole from an acetyl molecule including a dipole in another asthma molecule well it is um it is dipole but primarily it's going to be the hydrogen bonding next um the diagram above represents four cations also shown to the same scale which could I will be predicted by Coulomb's law to have the strongest ion dipole attraction to water and why okay the strongest ion dipole attraction to water all of them carries the charge but um just like um just like the iodipo force within the ionic bonding the greater the charge the greater the um the greater attractive Force so of course magnesium or calcium which which carries of the positive two charge will have a greater ion dipole attraction okay then out of these two the size matter okay so according to Coulomb's law force is equal to the constant K times q1 Q2 which are charges divided by r squared r represents the distance between the center of two charges okay so magnesium has a smaller distance or a smaller radius which means it will be it can get closer to the water molecule um so a greater charge and then the small radius result in a greater force so magnesium caused the largest charge to size ratio next a solid component group one Alkali metal and a Group 17 halogen metal dissolve halogen element dissolves in water the diagram above represents one type of solar particle represented present in a solution which of the following identifies the solid particle and best helps explain how to solar particle interacts with water molecule so obviously these will be the water molecules and then this is on the this is either The Alkali metal cation or the halogen anion water has a chemical formula of H2O so two hydrogen and one oxygen so obviously these small balls represent a hydrogen and then these bigger well represent the oxygen because the oxygen is facing toward this ion it means that this ion carries the opposite charge which is positive charge either C or D in a Russian or iron dipole interaction or the dipole double attraction because um the IRA in the center carries one whole charge of positive one or positive two so it will be the iron dipole interaction the attraction between the polar molecule and an ion so dipod double induction occurs between the two molecules the next is covalent Network structure which is is a very special type of intermolecular force so covalent Network structure means that one atom is bonded to every outer atom and then a large amount of atoms together form a three-dimensional Network structure and how it is different from a regular molecular solid is covalent bonds basically just Bond like couples of atoms together to make sure that they behave as a unit such as H2O such as CO2 but when it comes to covalent Network structure there is no clear cut as a whole unit or a molecule one atom is just bonding to another another is bonded to another atom another atom bonding to another atom so they just form this whole this large Network structure here are Ella trips of the carbon electrop it means different physical forms of the same element all of these allotropes consist of pure carbon all of them are pure carbon but they have different names they have different physical properties they have different application in real world it is because they are bonded and they form a different three-dimensional Network structure so let's say for graphite they form a layers and then for Diamond they form a very rigid tetrahedral structure around every single carbon atom in the fillerine it forms the football shape nanotube it forms the tube shape graphene it's a very thin layer or just a very thin sheet the covalent Network structure explains high melting point and high boiling point of these covalent Network solids and it is because it takes a lot of energy to break these bonds well first off covalent bond is a chemical bond which means it is way way more stronger um than the intermolecular force such as learning dispersion force um and dipole-dipo interaction or hydrogen bonding that's one of the reasons the second reason is that the atoms are bonded to one another endlessly so if and if part of it part of the covalent bonds have been broken just like the hole on this fishnet tights on the other atoms the and these atoms are still bonding to other atoms so the whole structure is still maintained so if you want to melt the covalent Network solids into liquid you will have to break every single Bond every single covalent bond and then that takes a lot of energy a huge amount of energy so that's why it has high melting point and high boiling point it also explains the rigidity and the hardness of the covalent Network structure and only the no Metals such as silicon or carbon can form the covalent Network structure so here are a couple of examples of covalent Network solids that you will see often in AP Chemistry exam one is diamond and the other one is graphite we know that both of them consist of pure carbon but they have different properties this is because they have different structures so um carbon has four valence electrons which means it can form up to four single bonds with another atom so in the diamond one single carbon is bonded to four another four outer carbons well one carbon in the center one two three four it forms four single bond with outer carbons and every single carbon forms one two three four again one two three four every single carbon forms four carbon-carbon bonds and this means that the diamond structure is very very stable the bond angle is um and the bonding is fixed you cannot stretch it or compress it and it's uh it has extremely high boiling point and melting point the melting point of diamond is approximately four thousand Celsius degree which is extremely high on the other hand when it comes to graphite well graphite is used in pencil so it's soft this is because the graphite is consists of the layers of the carbon covalent Network and in between the layers there is only weak body Force but within each of the layer the carbon atoms are covalent covalently bonded to each other so it's very difficult to just destructure the layer but it's pretty easy for layers to slide past each other and the difference is in graphite each of the carbon is body two one two three three undercarbons by single bonds okay again one carbon is bonding to three hydrocarbons by single bond which means the carbon will be left with one single electron because it has four valence electrons in total and each of the carbon carries one single electron so it eventually these electrons can form weak bonding force in between the layers also these free electrons are free to move because when this electron moved from this carbon to the next carbon this electron can move to the next one and then the electron move to the next one and then the next one and then it goes on so electrons are free to move within the layer this explains the conductivity for um the the graphite on the other hand there is no free electrons for Diamond so it's a poor conductor um and the the melting point of the graphite is approximately the same it's 3 600 Celsius degree because it also takes a lot of energy to break all of these covalent bonds the next is silicon dioxide and silicon carbine so silicon just like carbon um is in group number four and then it has four valence electrons so it can form a maximum of four single bonds okay and in silicon dioxide one silicon forms four single bonds with oxygen and then each of the oxygen forms two of the single bonds with a silicon well one silicon bunny two one two three four four oxygen and one oxygen is bonded to one two two of the silicons again because this is a covalent Network structure every single atom is bonded to every other atom and there is no clear cut as such a thing called molecule so I don't even know if this is this behave as a unit or this Behavior behave as a unit or this now there is no clear cut off of of a whole unit called molecule and silicon carbide so silicon and carbon both of them have four valence electrons so just like the diamond structure each of the Silicon is bonding to four of the carbon each of the carbon is bonding to four silicon so it's a extremely stable and it's extremely stable structure with no freely moving electrons the diagrams above represent two allotrophs of solid phosphorus which of the following correctly identifies the electrode with a higher melting point and explains why okay so now we need to compare the intermolecular force the higher intermolecular force means higher boiling point because it takes more energy to break the bond the electro one of the foods first obviously they are individual units okay so this is molecules and on the right hand side the electrop two okay so each of the atom is bonded to every other atom and there is no clear cut of a molecule or a unit so this is a covalent Network structure and obviously it takes way more energy to break the covalent bonds in Electra 2. so the answer will be either B or C let's take a look at the reasoning B because the it has covalent bonds between the first atoms that are stronger than the dispersion force between P4 molecules and Electrode one that is the correct answer what about C because it has a metallic bonding that is stronger okay first off phosphorus is non-metal so of course it is not going to be the metallic bonding so the answer is B next the structure of two allotropes of carbon one is Diamond one is graphite I represented above which of the following statements best helps explain why diamond is much harder than graphite again diamond is bonding to one single carbon in diamond is bonded to four carbons one carbon in graphite is bonding to three carbons in a diamond contains covalent bonds where a graphite contains ionic bonds okay this is completely not true both of them contain covalent bonds and B Diamond contains ionic bonds okay again this is not true see carbon atoms in Diamond have four covalent bonds whereas graphite is made of layers that are held together by relatively weak dispersion force that is the right answer as I said each of the carbonyl graphite has one free electron and then these three electrons form weak binding force in between the layers and this is a weak dispersion force the carbon atoms in Diamond have a sea of mobile electrons this is not true so electron C model is is only metallic body so here is a review of all all types of the solids ionic solids versus molecular solids versus metallic solids versus covalent Network okay so what are your properties um what are your properties so for Ionic solids they have high melting point and then the high boiling point because the ionic bonds are strong it takes a lot of energy to rate that ionic bonds and it it does conduct electricity in liquid and accurate stage but not in solid state so it's a poor conductor and solid but good conductor in liquid and the accuristine when dissolving water and next molecular solid so molecular solid means it behave as a unit called molecule and the molecules within the molecules atoms are bonded to each other by covalent bond and in between the molecules there are intermolecular forces and depending on the intermolecular forces the melting point can be high or more low and the boiling point boiling point can be high or low but in general compared to ionic solid molecular solids are considered to have low melting point and low boiling point and the next is metallic solid so metals have electron C models which means delocalized electrons are free to move around which makes it a good conductor of electricity no matter it is in solid phase the liquid phase or the gas phase and then usually it has high melting point as well also it is known for its malleability and ductility and this is because um the the metallic ions the metallic cations can rearrange themselves um without breaking the bonds due to the electricity model the last one is covalent Network structure so such as diamond or graphite one atom is bonding to every other atom and a large amount of atoms are covently bonded to together to form a three-dimensional Network so it has a very high melting point and the boiling point because if you want to melt the solid into liquid for the covalent Network structure you will have to break the covalent bond which is much stronger than the intermolecular force and usually it is rigid and hard next I will try to explain how intermolecular forces are related to different phases solid liquid gas so the strengths and types of intermolecular force determines the properties of the liquids and solids such as the boiling point and then the vapor pressure so for example if intramolecular first within a molecule is considered to be pretty high then the boiling point will be pretty high okay high boiling point means that there are very few of the liquid particles liquid molecules that will evaporate um or escape from the the liquid surface so it's a vapor pressure will be relatively low on the other hand if the intermolecular force is relatively small then its boiling point will be relatively low as well which means a lot of these molecules will easily escape the surface of the liquid and then the vapor pressure will be pretty high let's try to compare the solid liquid and gas of the molecules so usually in the solid the motion of the particles are very very limited which means the particles can only vibrate in the position but they cannot move move to the other side of another another particle so this explains why the volume is fixed because they are tightly bonded to each other and then on the space between there's barely no space between the particles and you cannot compress them anymore and then you cannot stretch it also usually the shape is fixed well it's not it does not apply to all of the solids some of them have um some of some of them is like soft um but for most of the solids they still maintain the ship unless you push it or give it a pressure for the liquids okay so liquids um it's a little bit similar to the solids so in liquids particles are in closed contact with each other but they are not arranged in this letter structure which means they don't have to be fixed in a specific position they can slide um around each other so they can change the positions so the particles are constantly moving and colliding um it can slide past each other which explains why liquid is of uh is fluidity and then what it explains why liquid has no fixed shape but its volume is fixed and its volume is about the same as the solid of the same substance it's because the particles are still in close contact with each other um so there's not so much space So In general the amount of volume it occupies will be the same or it will be similar to the amount of volume occupied by the solids and the next is guess and gas particles are far away from each other and then gases are in constant motions and this means the attraction between the particles is the minimal out of these three phases this allows the particle yes particles to be away from each other so there is no fixed volume and then no fixed shape next I will talk about two different forms of the solids one is amorphous the other one is crystalline so usually we learned that um in solids particles are highly ordered and they're arranged in this letter structure that is actually the crystalline and for some of the other solids that they are in the form of the amorphous which means they're not in this regular ordered Arrangement so this is an example of the this is arrangement of the particles in a Murphy solid and some of the um some of the solids some of the soft or the flexible solids such as a rubber or the cotton candy has this amorphous amorphous form on the other hand for the crystalline it has very very ordered and regular three-dimensional structure so snowflake is a typical example so snowflake is an example for the crystalline solid the next is the ideal gas law we talked so much about the solid molecular solid metallic solids covalent Network structure now we are going to talk about the guess um so first off there is such a thing called ideal gas of course it's impossible it does not apply to our Real World um this is just based on the assumption that all the gas particles are very very small it occupies a very small space within the container and then each of the gas particles are far away from each other and then there is no attraction force or republican repulsive force in between the particles So based on this assumptions we call them ideal gases because we believe that they behave in an ideal way and for all types of Ideal gases they follow this equation of P times V is equal to n times R times t p of course refers to the pressure the reference to the volume of the container obviously and refers to the number of the moles of the gas particles and R is the gas constant and T is the temperature and remember that the temperature in this formula has to be measured in the unit of the Kelvin and I want to talk about the pressure first so when we talk talk about the pressure a lot of people think that um it represents how hard the gas particles hit the the wall of the container that's not true the pressure is actually related to the frequency of the Collision so that's why if there are a lot of gas particles in the container then the pressure increases not because each particle hits the wall with a uh with with a greater force um it's because there are just more Collision on in one single second compared to like very few gas particles a gaseous air fuel mixture and sealed car engine cylinder has an initial volume of 600 milliliters at One ATM to prepare for ignition of the fuel a piston moves within the cylinder reducing the volume of the Airfield mixture to 50 milliliters okay so the volume has changed from 600 to 50 milliliters at constant temperature assuming the ideal Behavior which means I can apply the ideal gas law PV is equal to nrt what is the new pressure of the air fuel mixture okay so PV is equal to nrt and then now the temperature is the same and it's the same sample which means the number of moles of the gas Supple has not changed so for these two samples for the first one I can write it as the pressure times the volume pressure 1 times the volume one is equal to the number of mole times the gas constant R multiplied by a temperature and after the compression the T has not changed number of moles has not changed so it is the same as P2 times V2 So eventually I will have P1 V1 is equal to p2v2 okay so V2 the new volume will be equal to p1v1 over P2 or 600 milliliters multiplied by 1.0 ATM divided by 50 80 50 milliliters which is 12 ATM so it is 12 times as as big as the original pressure so it will be the right answer will be B about 12 ATMs the next and 10 Celsius degree 20 grams of oxygen gas exert a pressure of 2.1 ATM in a rigid 7.0 liter cylinder assuming ideal Behavior if the temperature of the gas was raised to 40 Celsius degree which steam would indicate the new pressure and explains why okay so now this time the temperature has changed um and uh it is in a richest 7.7.0 liters which means the volume is fixed so again applying the ideal gas law of PV is equal to nrt okay so uh what has changed is the temperature and then the number of moles of the gas has not changed the r gas constant doesn't change and then the volume has changed so what has changed must be the pressure okay so now I know that P1 times V is equal to nrt1 P2 times the V is equal to nrt2 okay so I can just use ratio and then come up with this the ratio equation of P1 over P2 is equal to T1 over T2 P1 is 2.1 ATM over P2 is equal to T1 which is 10 Celsius degree plus 273 to convert it to the Kelvin over 40 plus 273 again converting to Kelvin so 2.1 over P2 is equal to 283 over 313. so P2 is equal to 2.1 multiplied by 313 over 283 so the right answer will be um 2.3 ATM because P increased by the proportion of 313 over 283. remember that pressure occurs when the gas particles collide with the wall of the container or heat the wall of the container if you have a a batch of gas particles all mixed together such as nitrogen gas and oxygen gas then the number of the gas particles does matter to the partial pressure because partial pressure means the pressure applied by each of the gas particles and the pressure depends on the frequency of the Collision so pressure does not depend on how hard the gas particles are hitting the wall it depends on how many times the gas particles are hitting the wall in the unique unit period of time which is in one second which means the more of the nitrogen gas you have then the more collision between nitrogen gas particles and the wall if you have fewer oxygen gas um on the other hand then the fewer collision between the oxygen gas particles and the wall which means the partial pressure of oxygen will be lower than the partial pressure of the nitrogen gas so in total the total pressure of this gets sample um is equal to the frequency of all the gas particles hitting the wall so total pressure is equal to the sum of all the partial pressures in this gas sample in this example total pressure is equal to partial pressure of nitrogen plus pressure pressure of oxygen well then as I stated before the partial pressure for each of the gas species depends on how many moles you have for each cat species and this is represented as the mole fraction so the partial pressure of nitrogen gas is equal to the part the total pressure multiplied by the mole fraction of nitrogen which is calculated by number of moles of the nitrogen gas divided by the total number of mole of the gas particles and that's the same for the partial pressure of oxygen that is equal to the total pressure of this gas sample multiplied by the mole freshen of oxygen which is number of moles of Austrian gas over the total number of mole of the gases two distilled a rigid 5 liters container each container gas at the same temperature but a different pressure as shown above also shown are the result of transferring the entire content of container one to container two no gases escaped during the transfer assuming the ideal Behavior which statement is correct regarding the total pressure of the gases after they are combined first off it occurs this transfer occurs at the same temperature the initial temperature of these you get samples are exactly the same and then when you combine them then the total pressure as I stated before is equal to the sum of the pressure pressure for all of the for each of the gas species so partial pressure of oxygen gas plus partial pressure of nitrogen gas and because when when you transfer it there is no change in a temperature or the volume which means according to ideal gas law PV is equal to nrt when there is no change in the volume no change in the temperature and then it's exactly the same amount or the same number of moles of the oxygen gas transferred and R is a constant so P does not change the pressure of the oxygen does not change during this transfer which means the partial pressure of oxygen is still 0.8 ATM and the pressure of nitrogen is of course still 1.0 ATM so they add up to 1.8 the right answer will be a the total pressure is the sum of the initial pressure and it is because the the total pressure only depends on the total amount of the gases yes so it doesn't really matter if this is oxygen and let's say this is a helium gas or the xenon gas or this is a Neon gas or carbon dioxide carbon dioxide yes it doesn't matter given that it is still at the same temperature and then it it's in the container at the same with the same volume then the result the total pressure for this result will be exactly the same so be lower the total pressure is lower not true C the total pressure is higher is not true D the total pressure cannot be determined well it's not because the temperature is not given well temperature is not given true but it does not really matter if the temperature is low or high what really matters here is that the temperature has not changed the temperature is held constant so I can apply to ideal gas law and then figure out that the pressure of the oxygen has not changed during transfer so I can just mainly just add up the the pressure pressure of oxygen and nitrogen so D is not true either next let's talk about the real gases up until now we were dealing with idea guesses their behaviors um and the ideal gas law PV is equal to nrt but of course nothing in real world is ideal okay especially when it comes to real guesses so real gases show some behavior that deviates from the ideal gas law so on the left side this is a model that shows the ideal gas on the right side that is a more accurate model of the real gases and let's take a look at how different they are for the ideal gases we assume that the the gas particles occupy very very very little space and then we assume that primarily it's just the empty space the volume and then we also assume that gas particles are far from each other and then we also assume that there are no attractive force or non-repulsive force between the gas particles but all of these are just the most ideal situation which does not really occur in real world in real world gas particles um in between gas particles there is some kind of Attraction which is intramolecular forces and these intermolecular forces get stronger when guest particles are closer to each other and then when does this happen when at high pressure this deviation phenomena is enhanced because at high pressure it means that there are a lot of gas particles packed together in a small container within a small volume so gas particles get closer to each other a greater intermolecular force occurs and then it makes the deviation greater and it also occurs at low temperature so at low temperature gas particles are moving at a slower speed this means that because of this slow speed um the report they they are they are not free from the or they're more Bonnie too they're more affected by the intermolecular force so high pressure and low temperature are two conditions that affect the real gases and then enhance the deviation of real gas Behavior real gas from ideal gas behavior and one more factor that affects this is the size of the gas particle so as the guest particle size getting bigger and bigger then at the high pressure compared to a small size gas particles the big size gas particles will be closer to each other even at the same same high pressure because it just occupies the space by itself and we will use kinetic molecular theory to explain some of the properties the macroscopic properties of Ideal gases when I say macros bucket scopic properties it's something that is um that can be observed by human beings by us let's say the temperature of this gets simple or the pressure or the volume these are considered macroscopic properties we're not really taking a look at e in the visual gas particles we're taking a look at this whole batch of gas particles as one single sample that's why we call it macroscopic perspectives so such as temperature such as volume such as your pressure Etc and we're going to use kinetomolecular Theory to explain it in terms of the motion of each of the particles so kinetic molecule Theory assumes that individual gas particles are going through the continuous random motion so when I say continuous it means that the gas particles never stop they're always in motion they're always moving and when I say random it means they're moving into random Direction and at random speed if all the gas particles are moving in the same direction then this is not random motion for sure and if they're moving at the same speed then this is not random motion eater so even if this whole batch of gas particles share the same volume same pressure and then the same temperature but actually if you take a look at individual particles they behave in a different way some of the particles are moving at a higher speed some of them are moving at a very low speed some of them are moving at the same speed but at different directions this is what we refer to as the continuous render motion and I can try to visualize the this type of continuous render motion by Maxwell boltzmann distribution this is a really really important distribution curve okay so because this is a distribution curve um it means that end is simple there are a lot of gas particles and each of the gas particles actually have different values of the kinetic energy so kinetic energy is equal to one-half times the mass times the velocity squared or the speed squared so for each of the gas particle they have the same same mass so if m is the same but they have different speed which result in different kinetic energy for each of the gas particles so on x-axis I'm going to put the kinetic energy of the particles on the y-axis I put number of the gas particles or sometimes it says the percentage of the gas particles or proportion of the gas particles they basically mean the same thing well usually in an AP question question it's going to give you two different curves to compare them this is where a lot of people get the mistakes because they think the lower curve the lower Peak means that oh it's the lower kinetic energy the higher Peak means that it's a high kinetic energy that's not true at all okay that's the opposite so the this lower curve the blue one it represents a gas sample at higher temperature and then this pink one with a with a higher pick represent a gas sample at a low temperature okay and I will try to explain it um using a metaphor on the x-axis I'm going to put the SAT score on the y-axis I'm going to put the number of the students and now we're going to compare the SAT scores of the students at two different schools one is school a the other one is called B and this is a curve for school a this is a curve for school B okay so does it mean that school a is in general um have a better academic performance than School B and no that let's break it down for school a and for both School A and B there are people who School very low for sat like um this means like very very low for the sap score and this means very very high for the SAT score but how many students are there in school A and B who are scoring very low for school a probably we have 10 students who are scoring extremely low for school B we might have only like one student for um and then for the next for the next lowest common score there are let's say 20 students in school I who scored this much in school B we can only find five students who are scoring this much so in in conclusion in school a does high pick means that a lot of students in school a are scoring in this range on the other hand in school B most of the students are scoring this range so in comparison School B in general School B students are scoring higher in sat compared to school a so this higher Peak only means that many many students are having the same SAT score which is Discord in school B and then in school B many of the students are scoring this score which is a higher score so in general who is doing better and when it comes to sat School B is doing better so this is what I mean by the distribution curve so the height of the peak only represents a frequency this is very similar to histogram that you learn in math okay so going back to our guest samples so um let's say it's the same yes particles the same species nitrogen gas then the nitrogen gas at a lower temperature will have this higher Peak the higher curve this means that many of the gas particles in this low temperature nitrogen are having this low kinetic energy on the other hand more of the gas particles in this high temperature nitrogen gets simple are having a higher kinetic energy this is really really important and sometimes you are given the average speed on x-axis or um or average kinetic energy or kinetic energy on x-axis so you really need to pay attention to it the next is the difference between average kinetic energy and average speed first off average kinetic energy of any of the gas particles depends on temperature only this is a very very very important this means that if you have the gas particles if you have two different yet samples one is nitrogen gas and the second one is oxygen gas well obviously there are two different species but given that they have the same temperature and let's say 300K then the average kinetic energy for these two samples will be exactly the same because they have exactly the same temperature and it doesn't matter if you have a lot of nitrogen gas or very little of oxygen gas um it doesn't matter the species of the gas particles it doesn't matter what really matters is only the temperature but remember that this is not the kinetic energy for every single particle what I mean by that is average kinetic energy of this whole batch of the gas particles is the same but it doesn't mean that average speed of nitrogen gas and oxygen is the same as 300 account 300 Kelvin it's because kinetic energy is equal to one half times MV squared which means that given that nitrogen and oxygen have the same kinetic energy because it's the same temperature then at the same temperature of 300 Kelvin kinetic energy of um get sample one is equal to kinetic energy average kinetic energy of the gas sample two then one half M1 V1 squared is equal to one-half M2 V2 squared one half gets canceled out then V1 squared over V2 squared is equal to M2 over M1 or V1 over V2 is equal to the square root of M2 over M1 which means that the velocity of or the speed of the gas particles the average speed of the gas particles is a reciprocal ratio and then a square root and a reciprocal ratio of the mass which means if the gas particles has a greater molar mass then it moves slower and then if the gas particles has a smaller mass then it moves faster the conclusion is large molar mass of the gas particles means slower average speed okay so at 300 Kelvin this sample of nitrogen gas and then this sample of oxygen gas will have the same average kinetic energy but if we ever compared their average speed they are not going to be the same so which sample has a greater speed let's take a look at nitrogen gas and an oxygen gas on the periodic table so oxygen gas has a greater molar mass than nitrogen gas which means nitrogen gas will have a smaller speed it's smaller average speed compared to the nitrogen gas nitrogen gas is smaller which means they're more agile they're more free to move they can move more freely or faster so average speed of nitrogen gas is greater than oxygen this graph above shows how particular real gas debates from ideal gas behavior at very high pressure okay this means that there are a lot of gas particles in a small space based on this information which of the following is most likely the guess and gives the reason based on the kinetic molecular theory okay so it's genetic molecule Theory um then well so this is the idea guess and this is a real guess so at a very high pressure on the volume of the real gas is greater than the idea I guess well as I stated before ideal gas assumes that guest particles does not occupy any of the space it's just a dot but in in terms of the real gases it actually does occupy space so at very high pressure which means there are a lot of gas particles within a small space so the volume cannot be cannot be compressed as much as the ideal gas as for the ideal gas they can get closer and closer the volume they occupy can be only this much for the real guests the volume just cannot decrease as much okay so which one hydrogen gas nitrogen gas neon and then SO2 so I should pick something that has uh the greatest volume that occupies the greatest volume which is SO2 because it consists of three of the gas particles of all A and B consists of two gas particles C is a neon that's a noble gas and it consists of only one single guest particle equal molar samples of CH4 methane and c2h6 ethane are in identical containers at the same temperature the c2h6 ethene deviates much more from ideal gas compared to CH4 deaths which of the following best helps to explain this deviation a c2h6 molecules has have more hydrogen bonding um okay B uh more hydrogen bonding means they are attracted they're intermolecular force is greater um B c2h6 molecules have a larger more polarizable electrons cloud and CH4 molecules do c c2h6 molecules have a greater average kinetic energy than okay I know that I immediately notice is not correct because they are at the same temperature which means average kinetic energy is the same for these two uh gas particles D c2h6 have a greater average speed okay this is not correct okay so remember that velocity V1 over V2 that is a square root of reciprocal of the math ratio so it's M2 over M1 so obviously c2h6 has a greater mass which means it will have a lower average speed okay so the answer is either a or b c2h6 have more hydrogen bonding well even though both CH4 and c2h6 has a lot of hydrogens it does not it's not hydrogen bonding remember hydrogen bonding only occurs between the molecules when the hydrogen is covalently bonded to either oxygen or nitrogen or fluorine and then the hydrogen side is right next to the oxygen side or nitrogen side or the fluorine side of another molecule and then in both of the ethane and methane hydrogen is covalently bonded to the carbon only so a is not true the answer is B it has a larger more polarizable electron cloud which means the intermolecular force in the ethane c2h6 is greater than the intermolecular force in the CH4 so because of this Beaker attraction Force the c2h6 deviates more from the ideal gas behavior the diagram above used errors to represent the speed of a gas particle which of the diagrams best represents the speed of the particle of the gas at a fixed temperature and Y okay diagonal 1 and diagram two what is the difference in diagram one all the gas particles are doing are moving at random Direction which is good but each of the guest particles have exactly the same speed so the length of the arrow represents a speed in diagram two all the gas particles are doing constant random motion which means the direction is random and the speed is random as well some of them some of the gas particles are moving at a large speed some of them moving at a very small speed so as I stated before according to Maxwell boltzmann distribution curve not all the gas particles in a simple have the same kinetic energy or same average speed even though this whole sample have the same temperature so diagram two is the right answer so I immediately cross out A and B and let's take a look at the reason because the particles have a net kinetic energy of zero well the kinetic energy as I stated before average kinetic energy is always proportional to the temperature which is measured in kelvin so if average kinetic energy is equal to zero then it means that the temperature is equal to zero Kelvin what we call by the absolute zero and it's impossible in real world to be at Absolute Zero temperature it's impossible absolute zero means all the particles including all the particles stop moving no more no more electrons are not even excited and the the protons are not even doing the vibration this is actually an ideal situation which means that it's impossible to occur in real world the right answer should be D because the particles have a variety of different speeds which also matches the Maxwell distribution curve um you will see a lot of different average kinetic energy kinetic energy and different speed in a sample of in a batch of the gas particles next this is the maximum boltzmann distribution curve obviously the two gas samples represent in the graph above are at the same temperature again the same temperature it means these two gases samples they have the same average kinetic energy well even though they have the same average kinetic energy now on the x-axis this is speed not the kinetic energy so that's why these two curves do not match exactly and which of the following statement about the gas is correct well obviously guess X has a higher Peak but again this does not mean that guess X has a higher speed it means that guess X has a lower speed in general and gets a z has a higher speed in general okay which means the velocity of guess Z is greater than velocity of just x given that they have the same kinetic energy this means mass of the gas Z is less than the mass of the mess of the Jazz X so out of a b c d it is going to be the right answer is um gas Z has a smaller molar mass than gas X and B there are fewer molecules in a sample of gas Z than in the sample of gas X how we count the number of the gas particles in each of the sample is by calculating the area under the curve but now let's see that on the y-axis it's the percentage of the molecules which means you might have a greater sample greater sample of gas X and then a smaller sample of gas Z but now we're only dealing with the percentage we're only dealing with a percentage so it doesn't really matter for a guess X um the area under the curved gas X add up to 100 for the gas the area under the gas uh the gas Z curve also add up to 100 it will be exactly the same the next question is the diagram above shows the distribution of speeds for a sample of oxygen gas which of the following graph shows the distribution of speeds for the same sample at a higher temperature in dashed line okay so as I stated before a higher higher temperature means the average kinetic energy will get greater okay so for this sample right now the average speed will be approximately here so if at higher temperature it will have a greater average kinetic energy and greater average speed approximately here so you will have a little bit lower curve which is more widespread and which is more a skewed more toward right so the right answer is going to be C so C is the only one okay so both C and D have a curve that's skewed toward the right but these not correct because um all the speed has to start from zero so it starts from a positive number this is not correct and as this curve gets it is screwed toward the right the heat will actually get lower and lower and lower because um the area under the curve must add up to 100 and then this is a more widespread one then the pig has to be lower to get the same area as this curve Solutions and mixtures well I really deal with Solutions a little bit so Solutions um is a kind it's a type of homogeneous mixtures which means a different substance different pure substance are mixed thoroughly or mixed uniformly so that you can't really tell one substance from each other such as saline water um saline solution or sugar dissolving water you can't really tell the difference between um this um this this part of the um the saline solution and the other part of the saline solution that will taste exactly the same they look the same both are transparent and then they'll have the same concentration but solution doesn't have to be just solid dissolved in solid dissolving liquid it can be a mixture of gases let's say atmosphere atmosphere is a mixture of nitrogen gas oxygen gas a little bit of carbon dioxide and a lot of other um a lot of other Gases such as our carbon monoxide such as ozone on the sulfur dioxide Etc um so all because all of these particles are mixed thoroughly and you can't really tell the difference so let's say right now I live in Los Angeles and then if I move to San Francisco I will still breed the same air with the same proportion of nitrogen oxygen carbon dioxide sulfur dioxide and carbon monoxide so it's thoroughly mixed it's uniformly mixed so the the atmosphere is still considered a solution and then it could also be liquids dissolved in another liquid let's say I mix different types of oils I mix um canola oil I mixed the olive oil on the coconut oil I mix all types of oil together and then they just dissolve in each other very thoroughly they're mixed well then this is also a type of solution or alcohol mixed in water they also mix pretty well you can't really tell the difference it's still a transparent liquid that's another example of the solution so solution can be solids it can be liquids it can be gases and when we refer to solution um the whatever we dissolve we call it solutes so let's say for saline solution Sodium Chloride table salt is solute and in the water whatever the dissolve other stuff is what we call by the solvent and when they're mixed thoroughly then we form this solution so the solute particle is dispersed evenly within the solvent this is a solution and how we calculate the concentration of a solution is the concentration represented as capital letter M molarity is equal to number of moles of the solute over the volume of the solvent or the volume of the or the volume of the solution and we use the unit mole per liters or we use another unit the capital letter M some molar molarity so these are exactly the same unit and how we calculate the concentration of gas is well there is no um there is no solvent when it comes to gas so when it comes to gas particles we literally just divide a number of moles of the gas by the volume of the container number of the moles of gas over volume of the container this is how we calculate the concentration for gas particles uh 500 milliliters of accurate solution of sodium phosphate was prepared using 82 grams of the solute what is the molarity of sodium phosphate in the resulting solution okay so the molarity as I stated before is equal to number of moles divided by the volume of the solution so number of moles can be calculated using the conversion between the the mole conversion so mass is equal to number of moles multiplied by the molar mass remember that this capital letter M represents the molar mass while this capital letter N represents the molarity or the concentration the number of moles is equal to mass divided by the molar mass so 82 grams over 164 grams per mole then it is 0.5 mole so I plug it in then 0.5 mole divided by the total volume of 500 milliliters remember that the uniform molarity has to be mole per liter so I will have to convert 500 milliliters into the liters which is 0.5 liters so for the answer I got 0.1 mole per liters or 0.1 molar the answer will be D how many grams of sodium chloride are needed to prepare 100 milliliters of 0.25 sodium chloride solution so the volume of the solution is given molarity of the solution is given again number of moles again uh molarity is equal to number of moles of the salt solute number of moles of solute divided by the volume of the solution if I rearrange the equation then I get n is equal to molarity times the volume so 0.25 molar multiplied by all 100 milliliters again I will have to convert it to the liters which is 0.1 liters the answer is 0.025 moles and I will have to convert it to um the the grams then mass is equal to number of moles multiplied by the molar mass 0.025 moles multiplied by 58 grams per mole is equal to um okay so that will be um 50 5.8 divided by 4 the answer is d so substance with similar intermolecular force tend to be soluble in one another this explains exactly why the the ionic compounds such as table salt dissolve so well in water molecule because water molecule in within within the water molecule the hydrogen bonding plays a crucial role and the sodium ions and the chloride ions which are cations and anions they carry a charge so they form a ion dipole Force which is considered pretty strong and when it comes to dipole forces dipole forces forms between the partial charges which is also charges so according to the Coulomb's law they form a strong intermolecular force this is why the ionic compounds dissolve pretty well in water on the other hand water and oil do not mix well this is because in oils oil consists of primarily long hydrocarbon chain very very long hydrocarbon chain it might have a little bit of oxygen or nitrogen but most of it is just hydrocarbon so in between different hydrocarbon chains they form a strong London dispersion force in between them they form strong London dispersion force so this is why different types of vegetable oils are mixed well with each other but in between the water molecules and then the low hydrocarbon chain they do not form a strong intermolecular force and they don't actually have a similar intermolecular force for low hydrocarbon chain London dispersion force is the most important one and when it comes to water the dipole damper interaction and hydrogen bonding is the most crucial one so they do not have the matching intermolecular force that's why they do not dissolve well in each other methanol ch3oh dissolved completely in water to form a solution that does not conduct electricity which of the following diagram best shows the major type of attractive force that exists between the particles in the solution ch3oh I immediately know that a is not the right answer um ch3 ch3 and then oh well so the methanol has to be one single molecule but now I see this dashed line which means it's the intermolecular first within the methanol and then the hydrogen on the methanol forms a covalent bond with oxygen this is not right um the next B ch3 oh okay again I don't see that hydrogen the hydrogen for some reason is attached or bonded to covalently bonding to the water molecule this is not right methanol has oxygen and hydrogen so it has a hydrogen bond into an oxygen which means it is able to form a hydrogen bond and hydrogen bond forms between the hydrogen of one molecule and the Highlight electronegative atom on the other molecule which is oxygen or nitrogen or fluorine and remember that this hydrogen must be covalently bonded to oxygen or nitrogen or fluorine because um this is this makes sure that the hydrogen carries the partial positive charge and oxygen of course carries a partial negative charge so they attract each other and D is not the right answer because it forms some kind of intermolecular force between the oxygen two of the oxygen atoms in massano and oxygen but in both of the cases oxygen carries the partial negative charge and light charges Propel online charges attract so so they wouldn't form any of these intermolecular force which of the diagram above bathroom present the interactions that are responsible for the relatively large solubility of potassium chloride crystals in water and wine I know immediately it is dead diagram one when it says it's a large solubility which means it dissolves pretty well it means ionic compounds dissolve into cations and anions and each of the ions are surrounded by water molecule and for the cations such as K plus it will be surrounded by water molecule but oxygen facing it um and the chloride the the negatively charged anion will have hydrogen facing it so the answer is diagram one um because of the strong iron dipole interaction that's the perfect one so the oxygen side of the water molecule and then which carries a partial negative charge and then the the cation which is a ion they form ion dipole Force the same for the chloride ion it's a negative charged ion and then the hydrogen side carries a partial positive charge so they form a strong ion dipole interaction next let's talk about how do we separate the mixtures from each other um the easiest one is filtration so filtration is used to separate the heterogeneous mixture especially something that is insoluble in water if a substance is insoluble in water or the actual solution then I can use filtering filtration to separate these two I will use the funnel the gas fennel and then inside of funeral we're going to put the filter paper of course you will have to rinse the paper with distort water and then you are going to put the funnel over the beaker or the flask um and you're just going to gradually pour the um the mixture inside of you know inside of filter paper and then the filter paper will um the solution the Acura solution will get through the filter paper and then it will be collected when in the in the flask or in the Baker on the other hand The solid residue which cannot be dissolved in actual solution is left over inside the filter paper and once you get The solid residue what you usually do in the experiment is you are going to rinse it you're going to rinse it multiple times to make sure that it doesn't have um much of the actual solution left over and then next you are going to dry it and then next you are usually going to measure um its weight and then you go you can figure out the number of moles or the mass of this solid residue next is distillation so distillation is um used pretty often um and it's used to separate um the the soluble mixture the the solutions from each other and it's especially useful when it comes to separate two liquids from each other so let's say you have a mixture of alcohol and water they mix thoroughly and you cannot use evaporation because for evaporation you will get all the water out and then you are left with a solid residue such as such as um table salt dissolved in water but alcohol and water both of them will evaporate so evaporation is not a good appropriate method for the mixture of alkaline water but you can use distillation so for distillation you are actually taking advantage of the fact that they have different boiling point so water has a boiling point of 100 Celsius degree alcohol as a boiling point of approximately 75 Celsius degree so um you were first off you are going to pour the you're gonna put the solution um in this flask and then you are going to put a thermometer on it and you are going to carefully adjust the temperature you are going to raise the temperature gradually to um some a specific temperature that's slightly above the alcohol boiling point let's say approximately 78 Celsius degree so what's going to happen is only the alcohol will evaporate well actually a little bit of water will be evaporated as well but the amount is small so it's negligible so all the alcohol evaporate and then it goes up it becomes again a vapor it goes up goes up and then it's going to pass through um this um this tube because at the top it's sealed okay when the steam or the vapor passed through this um this tube it's surrounded by the condenser it's surrounded by the cold water the cold running water so the gas Vapors um condensates go through condensation and then it liquidifies again and then it will be collected in this flask So eventually um when this reaction is done you will observe no more change in the level of the solution which means only the water is left and then in this flask you will have only the alcohol and probably a little bit of water as impurities in paper chromatography how we do the experiment is we're going to draw a line here at the very bottom and then I'm going to put a drop of the solution and you can have you might have a lot of different types of the like pure such as mix in this solution and then you are going to put it on the solvent but remember that the solvent the solvent level has to be lower than um lower lower than the spot of the of the solution and then the solvent will go up along this chromatography paper and then at the same time the solution will actually separate into different pure substance um so it's so let's say for this example um the blue dye is moving the fastest that's why it goes up and then the purple is the second and then the red is the slowest so they have started at the same time but then the blue because of its higher speed it went up this much and this depends on the size of the molecule and then the polarity so usually we use a non-polar solvent so in this solution if one of the pure substogen is non-polar as well it means that it will just goes up with the solvent um very fast because um there is strong intermolecular force between um this so This pure substance and the solvent so they're kind of sticking to each other and then um and then this non-polar um this non-polar pure substance will just rise up faster but if it's something polar because between non-polar solvent and then the Polar Polar substance they don't form the strong intermolecular force um so they do not rise up as fast as the nonpolar substance and then the second factor is the size of the molecules the greater the size or larger the size of course it takes longer to move on because they're heavy and smaller the size it moves up faster the second type of chromatography is column chromatography so collochromatography is a pretty similar to paper chromatography the only difference is for the paper chromatography you dropped you put the drop of the the solution at the bottom of the chromatic curvy paper and then it rise up on the other hand for their column chromatic graphic you are going to put the solution at the top and then it's going to go down okay so again when you have a stationary phase you're going to put the you're going to fill fill it with stationary phase which is some kind of solid and at the very top you are going to put the mobile face and then you will load the sample so in the sample you have couples of different um substance all mixed together um and then um the sample will just go down gradually and depending on how depending on the polarity of the stage ring phase it's going to separate into layers if the substance has the similar type of intermolecular force as the stationary phase then it is for more strongly attracted to the stationary phase so it's not going to go as faster it's kind of stuck there if it's let's say let's say the Steph Curry phase is non-polar substance and then one of the substance in the solution is polar substance then polar and nonpolar they do not really attract each other they don't have stronger molecular Force then the polar substance will go down faster because it's not stuck sticking to the stationary phase when methanol and water are mixed together they form a homogeneous mixture based on on the information in a table above which of the following would be the best procedure for separating a mixture of methanol and water well they have pretty similar density so not very likely that they're going to separate and methanol um and methanol and water and the methanol also has the oxygen on and hydrogen bonding to each other with covalent bond which means methanol also has the hydrogen bonding so there mixed thoroughly you cannot really separate them they're not going to form two different layers like water and oil and they have different boiling point so we can use the distillation um to um to get the methanol and water separated from each other the diagram above shows a thin layer chromatograms chromatograms of the same mixture of two compounds based on the chromatograms which solvent would be the most effective at separating the two compounds if the same exclusion phase is used for calling chromatography so when we use the chromatography we want to see the separation between two liquids or like two substance as much as possible so we're actually looking for c um because for the solvent C it's very obvious that like these two dots are like separate from each other they're far they're furthest away from each other let's talk about electromagnetic spectrum so electromagnetic radiation em refers to electromagnetic it refers to all different types of light and a lot of a lot of different types of waves that we are familiar with such as um such as x-ray gamma ray microwave or radio wave infrared UV light and visible light all of them are considered electromagnetic radiation and then for all of these light they have the wave particle duality which means they have the property of wave they behave like waves sometimes they have the property of particle and some of the other situation they behave like a particle and then their speed is constant their speed in um their speed in vacuum is equal to 3 times 10 to the power of 8 meters per second okay then let's talk about the frequency and wavelengths so we use the grid letter Nu to represent the frequency and we use the weight Lambda to represent the the wavelength then as for the frequency we use the unit of Hertz or um per second for the wavelengths we use the unit for the lengths like meters or nanometers or other other types of other types of units when it comes to for for the length and we have we will have a formula of the speed of the electromagnetic radiation is equal to Lambda times Nu the wavelengths multiplied by the frequency okay then let's try to explain I will break it down into couples of the frequent I will break it down into a diagram and make sure that you guys can understand it okay so let's say um one of the wave let's say wave um let's say wave a has a frequency of one it means that every second it has one cycle one two three so every second it has one one cycle this is considered one up and down this is considered and back to the same position this is considered one cycle and then uh for every and then its wavelengths will be the amount of distance traveled by one cycle of the wave so from from here to here this is considered a wavelength for the Wave A on the other hand there is another wave which is wave B and wave B has a frequency of three which means for every second one two three it it um it travels three Cycles so in one second it goes by one two three in another second it goes by one two three in another second it goes by one two three three Cycles so for the wave B it will be one two three one two three one two three for every second for wave a it's one one one for every single second well but for every second both wave a and wave B they travel the same distance so this is the amount of distance they travel in one one second and it's always a constant so this explains why different types of the EM radiation EM wave have um different um have different uh different frequency and different wavelengths but in the end they have the same speed and this graph shows all types of the EM radiation that you need to know for AP Chemistry exam so on the left side it's gamma ray on the right end that's the radio wave okay so the gamma ray has extremely high frequency so on the left this is High new on the right this is um low new okay and again because the speed is equal to Lambda times Nu which means and while C is equal while C is always a constant this means Lambda and Nu the frequency and wavelengths they are reciprocal B Trader so high Nu means it's a very small wavelengths Lambda and very low new means it is a very large wavelength and you will have to memorize um we'll have to memorize their order so gamma ray is the highest frequency and highest energy okay and um remember that e is equal to the plant constant H multiplied by the um the frequency Nu so energy carried by the EM wave is proportional to its frequency so high frequency means high energy gamma Raya has the highest frequency and then it's X-ray and then ultraviolet and then visible light and then infrared microwave and radio wave okay so for the visible light on the lower energy side or or the lower frequency we have red and then orange yellow green and then blue and then um and then purple so purple is right next to ultraviolet that's why I mean this is exactly why ultraviolet is named ultraviolet because it's past the violin and infrared is name infrared because it's right next to the red so um ultraviolet has a greater frequency than infrared which means and when it comes to visible light the purple light has a greater frequency than um the when than the red light um and how I explain this high energy is well imagine the ultraviolet can actually cause some harms and damage on my skin because it can actually penetrates the the top layer of the skin on the other hand infrared is used um to let's say measure the body temperature and what they do is they just shut the infrared on my on my skin but it does not cause any of the harm like I'm not going to get a skin cancer because of infrared but you might get skin cancer from ultraviolet because it's actually causing a damage then what about F3 so x-ray can penetrate all the way like all of this like soft tissues um until it heats the it hits the um the very dense material on the bones so until it hits the bone after it can penetrate everything and gamma ray is very very very powerful it can actually penetrate the bone as well it can penetrate couples of centimeters of the aluminum the metals and microwave I mean it is used to it is used on for microwave microwave is literally named after a microwave and it is because the microwave makes the water particles and food like vibrate vigorously so the food um heats up fast and radio wave so radiovake has not really caused any of the damage um it cannot even heat up the food so it has a very very very low energy radio wave is just used for radio which we barely use these days a photoelectric effect is a phenomenon and it's actually one of the most important property it explains one of the most important property of the light um so when I refer to light we think that it's a wave it's a continuous wave but actually it's not so light is known for its um wave particle duality and the photoelectric effect is um a phenomenon that actually shows the particle property of of the light so as for the light light actually consists of the photon which is the light particles so there are a lot of like light consists of very very very very small light particles called photons we can't even detect them photos are massless um and photons are even smaller than electrons so we can't really detect it in like with raw eyes and each Photon carries energy so each of the photon particle carries energy just like uh when you throw a football or uh or or a baseball with a bowl carries energy and this energy is calculated by using the formula of um e is equal to H times Nu so H is plank constant which is equal to 6.626 times 10 to the power of negative 3 joules per second and new um even though it looks like um velocity V but it's not it actually refers to the frequency of the light so I just said light has the particle wave particle duality which means it has some properties of wave but it also has some property of the particle and this equation is used to calculate the energy carried by each of the light particle but in this equation we actually use the frequency of the light which is the wave which represents the wave part wave property of the light so what photoelectric effect describes is when some light Heats on the surface of the metal samples then the electrons are on the sample of the metal sample then the electrons on the surface will be ejected if this energy carried by photon is large enough if the energy is large enough for electrons to overcome The Binding energy then they just they get ejected from the surface and they will actually carry that amount of energy which means there is a transfer between there is a transfer of energy between the uh the the photon the photons the light particles and the ejected electrons so this is actually really interesting so if you if I ever um Shine the surface of the metal with a low energy low energy light such as the red light then I do not observe any of the ejection of the electrons but if I shine it with a high energy light such as um such as UV UV light or the purple light then I will observe the injection of the electrons so this really depends on the frequency and the higher frequency means the higher energy carried by each of the photon in an experiment on the photoelectric effect a photon with a frequency of 7 times 10 to the power of 14 um per second okay so per second is the unit for the frequency was observed by a sample what is the approximate energy of this Photon so I will simply just plug in the numbers and E is equal to H times Nu H is again the plug constant 6.626 times 10 to the power of negative 34 joules per second multiplied by the frequency of 7 times 10 to the power of 14 per second so 6.6 times 7 well that is approximately 6 times 7 that's approximately 7 times 7 this is an approximate question so I'm not you're not required to use a calculator so 6.6 that's approximately seven so seven times six seven that's approximate that's 49 so it's approximately 49 times 10 to the power of negative 34 times 10 to the power of 14. so approximately that is 50 times 10 to the power of a negative 20 so that's approximately 5 times 10 to the power of negative 19 which is a electromagnetic radiation with a maximum wavelength of 540 nanometers so Nano is a unit um that's a prefix for the unit and it means 10 to the power of negative 9. so nanometer is equal to um one nanometer is equal to 10 to the power of negative 9 meters is needed for the study of photoelectric effect on the potassium atoms what is the approximate frequency that corresponds to this wavelength of 540 nanometers okay um so for any of the electromagnetic radiation when I say electromagnetic radiation it includes everything from visible light to infrared to UV to microwave to radio wave to gamma ray and X3 and then for all of this they share the same speed of 3 times 10 to the power of 8 meters per second so this is constant across all different types of electromagnetic radiation visible light the light of different colors like red yellow orange blue and purple all of them have the same speed and the UV infrared they all of them have the same speed of 3 times 10 to the power of negative 10 to the power of 8. and then how I calculate the speed um is speed is equal to Lambda wavelength multiplied by the frequency Nu then um three times then frequency Nu is equal to speed of the light divided by the Lambda wavelength so 3 times 10 to the power of 8 meters per second over of 5.4 times 10 to the power of negative seven which is approximately um so three divided by 5.4 that is approximately one half multiply by 10 to the power of 8 over 10 to the power of negative 7. so approximately one-half times 10 to the power of 15. so approximately 5 times 10 to the power of 14. the answer is D um absorbent absorption of the photon energy leads to different types of the molecule molecular motion and or electronic transition in a molecule or in an atom um so depending on what type of EM wave you dissolve you you absorb um there will be different types of the changes or transitions so let's say um some molecule or some atom absorb the UV wave or the visible light which has a higher energy then this molecule will go through the electronic energy we'll go through some transition on electronic energy levels so when I say electron energy levels it means um the electrons get excited it goes up and down so this is UV and the visible light and this is [Music] um transition on electronic energy levels so electrons are excited from ground state to let's say n equals one to n equals three electrons are excited from the second shell to the fourth shell this is the transition electronic energy levels and this is caused by a relatively high energy UV invisible light and next is infrared right after visible light is infrared so infrared cause molecular vibration um so uh molecular vibration so the bonds gets bent or Twisted a little bit because the molecules are going up and down vibrating but it's actually not moving um and then the lowest energy will be the microwave so when a molecule absorbs a microwave then the molecular rotational levels changes which means the module rotate from this position to like this position so it rotates like this way horizontally or it rotates it vertically and this takes the least amount of energy which of the following best explains what happens as photons of visible light are absorbed by dye molecules again either UV light or visible light will cause the the greatest amount of change in the molecule on the molecule which is transition of the electronic energy levels um then the answer is um certain electrons in a Dye molecules move to a higher energy with a difference in energy between the lower and higher energy levels being the same as energy of the absorbed photons a is the right answer B certain chemical bonds now die begin to bend and stretch while bending and stretching this is for the infrared um because the infrared cause molecular vibrational levels because infrared cause molecular vibration see the dark molecule begin to rotate faster in the certain modes okay rotating on the molecular rotation this is caused by microwave so not C and D um a certain covalent bonds in a dime molecules begin to break and reform where the bond energies of the bonds being okay so if you want a covalent bonds to break then it takes a lot of energy and then it can it's not caused by any of the microwave infrared visible light or UV one type of organic molecule can be converted to another type of organic molecule through an oxidation reduction process as represented in a diagram above which of the following best explains why infrared spectroscopy is a appropriate method to confirm that the product contains a carbonyl so carbonyl is a carbon oxygen double bond um a the absorption of inferior radiation caused the non-bonding electrons and oxygen to transition into a higher electronic energy level as I said the transition between the electronic energy levels is caused by UV or the visible light so a is not the right answer B absorption of infrared leads to an increase in molecular vibrational levels well this is the right one so banding of the bond or stretching of the bonds because molecules are vibrating but fixed in the position see absorption of infrared causes electrons and Pi bonds to transition to a higher bonding energy level again a higher bonding energy level will be caused by UV or visible the infrared relation radiation leaves you an increase in the molecular rotational rotation in the in the molecule is caused by the microwave so not b next is spectrophotometry so we learn um the basic the fundamentals about the fundamental concepts about the about the light we learned that the light half the wave particle duality and different types of EM wave has different frequency and wavelengths but they eventually have the same speed um okay then how can we use it in chemistry how can we apply it in chemistry um so we can apply the knowledge of the light to the chemistry to figure out that to figure out the concentration of a certain solution okay and here is a um here is a and here here it shows here in the diagram it shows how a spectrophotometer works so there is a light source um and then when it goes to the lens and then and when it goes through the monochromatter it's going to disperse into all different types of the waste a EM wave um so each of each of them carries a different um has a different wavelengths and different frequency and then now they're going to pass through this solution the sample this is the sample that we are we want to investigate we want to note our concentration open and then after it after the light passes it passes through the sample some of the light is absorbed and then some of the light passes through the past three and then eventually the detector will detect it the detector will detect it and then um based on the number in the detectorate then we know then we can figure out the concentration of this sample solution okay so let's say that sample solution is a blue then what color will it then what color does it then then it absorbs the red light the most actually it's going to also absorb all of the other lights as well but it will absorb the opposite color which is the red color the most so this is the blue color then it absorbs most of the the red light so for this spectrophotometry then I'm going to set the set the wavelengths as the wavelengths of the red light which is approximately 400 which is approximately 700 nanometers and then we can use beer Lumber law to figure out the concentration okay so beer Lumber's law state that capital letter A absorbers is equal to a times B times C and then a refers to the absorbance so it refers to the extent or that the amount of absorbance of the light and it really depends on the concentration C is concentration which means the darker the color or deeper the color the more absorbance occurs so light blue versus deep blue if um this if the concentration of the solution is larger than the color is zipper and then this solution will absorb more of the light and then B refers to the length of the qubit okay so in this diagram it shows that the sample solution is in a uh in a round like cylinder looking container which is actually not true so we use a very specific um container for for spectrophotometry we are going to use this Cube looking container and then we put our sample in it and then the width of this um the qubit or the length of the qubit represented B because the the because the more of the solution or the longer of the path the light passes through the solution then more absorbents occur so if this qubit is twice as long then the light has to pass through twice as much and then the absorbance will be twice as much and this small letter A represents the absorptivity so the absorptivity um represents how much a sample um or of the molecules or the ions absorb light at a specific wavelength so even for this one single solution for the same solution absertivity at different wavelengths is different so if you if you ever want to use beer Lumber law to figure out the concentration of a solution then you will have to calibrate the other on the other variables so you will have to set a to be constant which means for this machine you will have to set a specific wavelength and then you should use the same wavelengths across different trials and then you should use the same qubit or the same size of the qubit to make sure that the length of the qubit is the same and then you can just gradually increase the concentration and then um you will get a gradually increasing absorbance and then you can plot a diagram you can you can plot a diagram of a versus C and then you will absorb this linear relationship between the absorbance and the concentration the absorption spectrum of a certain red dye is shown above if a student analyzing the same concentration of this diet neglecting to wipe fingerprint of the qubit before placing it in the spectrophotometer how the absorption curve affected okay so remember that the more of the color or deeper the color the more the absorbance so fingerprint is just an extra layer of a color in it so it will actually increase the absorbance the answer is a The Pick of the Curve will be higher because more light will be absorbed um so a is the right answer B because the less light is absorbed no that's not right so with a fingerprint more light is absorbed shift to the left no it's not the shift to the right no it's not a student measures absorbance of a solution containing um iron thiocyanide ions using a spectrophotometer the qubit used by the student has two firsted walls and two transparent moles the student properly orients the qubit so that the path of the light goes through a transparent side of the cubits when calibrating the spectrophotometer how will the measured absorbance of the Iron style cyanide be affected if the student in currently orients the qubit so that the path of the light is through the Frosted sides of the qubit so the Frosted size Cubit means that it's going to absorb extra light um then uh the a the measured absorbance of the iron ciocyanide solution will not be affected not true of course it will be affected B the measured absorbance will be higher see the measure absorbance will be lower the the effect on the measure of surface depends on the concentration okay D is not right um well going back to the question how will the measured absorbance be affected okay okay um so because so it's very similar to the fingerprint question so the frost design will cause extra absorbance so the measured absorbance will be higher than the actual absorbance B is the right answer A student uses a spectrophotometer to analyze the solution of a blue food dye the student first reinses the pivot with distal water then the solution as the blue solution to the pivot forgetting to rinse the qubit with a blue dye solution first which means there are like leftover water inside a cupid the student places a cube in a spectrophotometer and measures absorbance of the solution assuming some distant water droplets were still in the Cubit which will dilute the um which will dilute the blue dye simple solution that I am investigating how would the measured absorbance be affected then when a diluted solution the measured absorbance will be lower than what than its actual value the measure of surplus will be too low because this water left will slightly dilute the solution um then a is the right answer