Transcript for:
Chemistry Fundamentals

you guys here is one of our first videos here about chapter 1 starting our class with studying chemistry I mean chemistry is the study of change so this is chapter 1 and we'll start to look at what does chemistry mean and I'm sure you guys have taken chemistry before or at least heard about it since you were low and you would talk about atoms and protons and neutrons and electrons and we'll be doing the same thing here but hopefully a little bit more depth so as far as chemistry this little hieroglyphic it's not hieroglyphic it's like a Chinese character that means change and that's what their word for chemistry is change so chemistry is the study of matter of courses so basically it's the study of everything and the changes that it undergoes often cause this is called the central science them it's like you need chemistry for everything you don't necessarily need biology for everything but you need chemistry for everything because it is the study of everything because it's the study of matter so you'll probably be required to take chemistry really no matter almost no matter what field you're in even psychology I think take chemistry so well I would say so considering you're studying the brain and the chemicals of the brain so basically it makes sense that chemistry is in everything so you see sanitation if we didn't have chemistry there would be a lot of human feces everywhere I mean actually there wouldn't it would just be umpires but at the same time the bugs probably couldn't keep up with it so what we do is we treat it with chemicals and we treat it in such a way as to isolate solids and liquids and treat it in different ways so Sam without chemistry sanitation would be not as sanitized if you will all these different areas of chemistry are involved as far as anesthesia vaccines antibiotics of course you'll see biology in here gene therapy of course understanding the genetic code those are chemicals that's nucleic acids as far as energy in the environment of course fossil fuels are as a chemical that undergoes combustion which then produces certain products so these are all chemistry related and nuclear energy is nuclear chemistry where you're studying the chemistry of the nucleus of the atom and how it undergoes changes materials and technology all these different materials are unique chemistry to understand polymers and ceramics all these different materials that do different things for us are come from chemistry molecular computing is a pretty neat field in which they're using molecules to do things as far as molecular switches food and agriculture of course if we didn't have GMOs even though I know that that is kind of a bad word nowadays those genetically modified organisms or crops help us to have larger yields pesticides of course in herbicides have helped us to have larger yields in food and agriculture but you could also argue it's destroyed a lot of the planet but hopefully chemists are learning from their mistakes and coming back with other chemicals or other more natural pesticides and herbicides that will help us to have a higher yield now how do we think like a chemist the fun part of understanding chemistry I think is understanding what's going on and things that you can't see so in this picture here I have a picture of a dissolving sugar cube so this you could just label as sugar now this would be of course--we're in chemistry so we're going to label it as a solid and it looks like it's dissolving so what's happening here these are called dissolving lines and these dissolving lines are actually a different density of the wrapper surrounding solution and that's why they reflect light differently now if you were showing this as a chemical reaction type of thing you might write the word sugar here and then you might put a cue or aqueous with it because now that's sugar but it's still sugar but now it's in the aqueous solution if this of course is water out here so I think that was a pretty neat picture that is in your book I believe now what I have here I don't know if I can show this I might have to show you during the WebEx this is a video and this video is showing a simulation of these are sugar molecules and then dissolving so I don't think it's gonna work here I'm gonna have to show it to you on the WebEx so how do you think like a chemist you see an anthill and you think ants you see a sugar go away you cute go away and you think where to go you know went molecularly into the solution here so thinking like a chemist is sleeping on the molecular level how there it goes so you can see that what's happening is the sugar molecules being drug away by the water molecules and the reason that's occurring is because of the interaction between hydrogen bonding between oxygens which red and hydrogen's which are blue white but what they're showing there is that there's an attraction and there was an attraction between the water and the sugar parts of the sugar molecule so this is a covalent compound sugar is so you didn't see it break apart you just saw it stay at an entire molecule of sugar so over here you'll notice that sugar stayed sugar but now has an aqueous label it didn't - I honestly am astiz envisioning it on in this fashion so again here's something thinking like a chemist here you have you see busting but you don't see you think what is rusting you ask yourself those questions what are the materials made of macroscopically you see the rust but microscopically you know that the iron is undergoing a reaction chemical reaction with the oxygen to make iron 3 oxide also known as rust so this is a chemical change and a chemical change is where it changes into new things so it when we think like the chemists we want to be able to write everything in symbols and those symbols indicate a few things they indicate who it is and they indicate its oxidation number oxidation number of iron in iron metal is zero and then when because it hasn't gained or lost electrons at this point and then it reacts with o2 now is that's elemental that's a gas and when there an element has not gained or lost electrons and then it made Fe 2 O 3 Fe 2 O 3 is one of the forms of rusty and the line form of rust and if we balance this it looks like I'm going to need to put a three here and then a 2 here and then a 4 here so that's a balanced chemical equation and that's showing that 4 irons and 3 o2 molecules combine to react and make iron 3 oxide so that's the microscopic or even sub microscopic I mean you have to have an electron skinning going on was thinking about chemistry and the scientific method you've probably heard about the scientific method often in your life but the scientific method is systematic approach to research usually there's some sort of observation then a hypothesis is put forward which is a tentative explanation and then you can test and modify this hypothesis over and over in this little euler fashion a hypothesis can then go on to be much testing and go to a theory and then to a law it can tell us information about the universe that it's the same in all those same conditions it's a law so like force equals mass times acceleration is always true it's a law a theory is it explains the body effects and tells us how and why something happens a law tells us what is happening that's the difference between these two things a law versus a theory a law tells us what a theory says how and why so the atomic theory is saying how and why atoms are arranged and why they undergo reactions the way they do so atomic theory explains matter in the form of atoms teeny teeny tiny so what is given is the study of matter and the changes undergo just like we already said now I have a video I want to show you here I think I'll show you down the webex but either way it shows how something is chemically changing so matter is anything that has occupy space and has baths now here's some definitions that's what we're doing here a substance is a form of matter it has definite composition and distinct properties very general terminology so all of these things that you see in the picture here is matter liquid nitrogen is matter in to gas gold ingots is matter and you would that would be au solid trying to draw a little s there and these zeros would mean it's not undergone undergone chemical combination and then this is silicon crystals and silicon silicon travels it travels individually I'm not sure sometimes things travels in fours like phosphorus travels but either way it's a solvent it's a middle point so this is all matter these are all substances so a mixture then it's a combination of two or more substances that retain their distinct identities so homogeneous mixture is a composition of the mixture that's the same throughout like soft drink milk or solder or solder is solder things together it's actually a 10 I believe lead intense an alloy a very low melting point and you can use that melting point low melting point to melt it and nothing's together like circuits but these are all from a genius milkis homogeneous throughout heterogeneous is not uniform throughout like the cement or iron filings in sand you can see the different parts of it so that's a heterogeneous nation physical now a physical characteristic or physical means can be used to separate a mixture into sphere components so physical means we're talking about being able to separate a mixture now this mixture cannot be chemically combined then and that's the point the the things in the mixture are retaining their own individual identities so physical means can then be used to separate them like a magnet or distillation so here's a magnet separating the iron from the sand and here's distillation that is distilling different types of liquids away from each other but the two different types of liquids will never chemically combined down here they were the same their individual identities now they just get separated through distillation so a physical means can be used to separate a mixture as they're not chemically combined because they were chemically combined they would not be an issue so let's talk about what an element is it's a substance that cannot be separated into simpler substances by chemical means cannot be separated into simpler substances so if you have a compound that could be separated into its elements like h2o can be separated into hydrogen of course and oxygen but then archives and oxygen are elemental so 114 elements have been identified think there's more than that at that at this point well 82 of them occur naturally like things like gold aluminum lead and so on these occur naturally but they occur usually in some sort of combination aluminum you don't find elemental in nature you find gold but aluminum lead all these things are in chemical combinations sometimes you can find mines of sulfur though which is pure sulfur like this 32 elements have been created by scientists so there's a usually in some sort of Collider where subatomic particles are smashed together or to medium sized elements and then larger elements are created here's some common elements and they're symbols so you want to know elements and symbols so how many should you know that's a good question generally I always tell people to know elements 1 3 82 now that is a lot for sure and you know sometimes you just have to memorize some things to really speak the language there are some things above number 82 that are pretty common like uranium uranium is a common element that you probably would see and you'll see ones above 82 also so just kind of have the periodic table next to you all the time and I don't expect you to memorize the periodic table but I do expect you to go nowhere o stands for oxygen au stands for gold so one through 82 for sure to know the symbol and their name but what is a compound now compound is something that's committed when elements chemically combined in a fixed proportion so all of these are compounds lithium fluoride is LIF that's the chemical formula for lithium fluoride quartz is sio2 and if that's an actual power of many of them and then dry ice is carbon dioxide so these are all compounds and which are more than one element combined in a fixed proportion and they can only be separated by chemical means that means you would have to to separate lithium from fluoride you'd have to do something to it to chemically alter it because when lithium fluoride to get into its elements you electrolysis you could use for this or something like that we apply some sort of energy to it and you can separate the elements and F two fluorines what are the ones that travels diatomic li so we would need to have it like that and then if we balanced it look like that I did put a phase labels on anything but either way that's a reaction now we would just want to touch on the three states of matter solid liquid and gas now that's important in chemistry is the fact that it's a solid label a liquid label or gaseous label and so this is just a your book had this picture of showing here's a chunk of ice and you see gaseous ice gaseous Isis gaseous water or water vapor and then solid water and you can see it's kind of neat that's my ice has a lower density than liquid water and then liquid water would have a liquid label and it has a certain type of arrangement of its molecules liquids are usually free-flowing solids are not free-flowing as a chunk they hold their shape and a gas would fill the entire container whether that was a room or just a small beaker but they cuz they are moving very fast they're very hot that's why they're a gas and they would occupy the whole container now different types of changes that occur like a physical change a physical change does not alter the composition or identity of a substance like melting we're dissolving dissolving is a physical change so when something dissolves in water it has an aging label and something melts it goes from a solid label to a liquid label a chemical change however does alter the composition so when you see something happening like hydrogen burning in air to form water that is a chemical reaction o 2 + h 2 to make h2o and this is like a little representation of it showing in molecule form these are molecules and all that the word molecule is used for covalent compounds so this is a molecule two molecules of hydrogen one molecule of oxygen will make two molecules of water and I want to show you this video probably on WebEx and that's where it shifts the changes chemical changes when sodium and chlorine react what this is showing here is the burning of ox of hydrogen so hydrogen must have been created down in this tube and then it was lit on fire and as it was being created it's burning with the oxygen in the air so as a chemical change as far as expense of an intensive properties this is a terminology used for certain properties of matter that depends upon how much matter is being considered an extensive property does depend upon how much like mass length they depend upon how much and volume and intensive perfect does not depend upon how much matter like density temperature and color it's an inherent property of something like I can have a big chunk of something or a small chunk of something if it's the same chunk it's the same thing it'll have the same density same with temperature in color now this is where you might want to go do fun sheets number 1 through 5 we've covered that material so the goal here is to watch these videos and then start working on those fun sheets and then during our web axing time we can address some questions on those budgets but let's continue on again matters anything that has mass and occupies space I feel like I must have a reason and that's because we're going into measurement measure is the clue when you measure mass you're actually measuring the quantity of matter now the quantity of matter is something that has mass and occupies space and it doesn't really matter where that matter is whether it's on the moon or on the earth if it's on the moon and the earth it's going to have the same amount of matter so it's going to have the same mass but it might weighs and make way differently but because weight is dependent upon gravitation pole so weight is the force of gravity exerts on an object now since we never leave the planet we always call we might use those terms interchangeably but something on the moon would weigh less but would have the same mass so one kilogram bar will mass at one kilogram on the earth and now as far as the SI units that we use to measure things to measure mass is the kilogram these are just SI units which means international standard international units and that just means that if I say hey I'm measuring this in SI units you what I'm talking about so that's really all there is to it you can measure lots of length in different units but the SI unit is the meter so you just want to be familiar what these units are so when I say put them in SI units you know what those units are time to be seconds electric iron amps and well I just whizzed by one of the slides that I wanted to show you I do have something in d2l for you and it's called SI units and conversion factors to print and I want you to print that only you don't have to but I you can use that on exams and so on on the previous slide there was the the conversion factors of the metric unit conversion factor so when you get a chance go to s go to d2l and look up the SI units and conversion factors to print it's in the syllabus module and a half of it looks like this it gives you all of these different formulas to interconvert various length units or mass or volume it gives you some conversion factors for any of these like imperial units inches and yards to the metric system and it also gives you some meanings for units of energy and also some formulas like here in Chapter six we use these Q equals M s delta T equation where Q means heat and that's something else that's on this sheet of paper for you to use in during exams and this here's a constant that's called the ideal gas constant and we'll use that in Chapter five so all these different pressure units have conversion factors and then our temperature as conversion factors and then the SI unit is given in each one of them below that in the gray area so let's keep on talking about measurement we can measure volume all the SI derived unit for volume is a cubic meter now a cubic meter is monstrous monstrously huge and that's why we don't really use that too often but it's the SI unit what we do use is a decimeter cubed which is actually a liter so we will see that a little bit more often because we use milliliters and leaders in our lab work and we also I want you to notice that one centimeter cubed is equal to one milliliter so we use density will be inter concluding between those there is down here again so if I say have a density for water of one gram per milliliter that's the same thing as a density of one gram per centimeter cubed so ball game a lot of times we'll use volumetric flasks and volumetric flasks only measure one volume this is a one liter volumetric flask so when you guys do your glassware scavenger hunt you're gonna see some things like oh how do I measure using a volumetric flask if I were to take a reading for this guy it would be one zero zero liters volumetric flasks usually almost always read to the hundredths place and so when even though it just says one here when you if you were to use this an experiment you would record three significant figures to it and these are your your certain digits here so anyway is just a little aside because volumetric flasks people are not as familiar with so they think oh it's just one liter but it only measures one volume and so you read to the meniscus and it's one point zero zero liters and there's that thing again you don't want to forget that because that's pretty common to use to interconvert those two so let's talk about density density is in grams per centimeter cubed and it's the amount of matter in a certain size of a sample so it's a reflective of how tightly packed the substance is so you could have a chunk of gold and if this was a chunk of gold and you had the same sized chunk of aluminum for example the same sized chunk of aluminum would weigh a lot less its met there I go it's mass would be a lot less because of the fact that aluminum is not as tightly packed so if you could zoom in on here the atoms of aluminum would be further apart than they would be in gold so density is reflective of the packing of the material actually in the sample so our opening photo we have this and I have here what for instance can be made about the density of the solution and what solution now this is a solution this is liquid water out here this is solid sugar so when you're dissolving this you make a solution and you'll notice that solution is sinking so that density of that solution should be higher and sure enough if you make a sugar solution it will sink to the bottom of your if you don't agitate it or stir it so remember density equals mass over volume so you want to keep that in your mind that that's a relationship of density so if we were to use this relationship a piece of platinum metal with a certain density has a volume what is its mass so you can use the depot's M over V relationship rearrange the formulas and you would get M equals D times V you're being asked for mass and when you do calculations always use make sure to include units and all numbers I'll kind of take points off for you if you don't because I get really lost in calculations sometimes if people don't include units so you'll notice here then the centimeters cubed cancels out and you're left in grams so that's how much mass would be in that size and there's the cancellation so your book gives you a little a little table here of densities and those densities are of some common samples of things like air ethanol water and they got osmium and it's the most densest element known which is more dense than gold it's probably worth more money to purified anyway so that's just to give you an idea as the density of some common materials so as far as temperature is concerned the temperature scales that we will be dealing with are kelvin celsius not fahrenheit but you know of course we still deal in Fahrenheit United States so we need to know the difference and how to inter convert them those formulas are given on that sheet that I wanted you to print out but we basically use Kelvin and Celsius for lab work and I want you to what I want you to notice here because this is important later when we do thermochemistry is that the the units between Kelvin and Celsius are the same size so if you were to look at the ticks on the thermometer that measured in Kelvin even though there's no such thing and the ticks that are in Celsius they're the same size so if you had a change in temperature say a5 it would be the same five degrees Kelvin five degrees Celsius it wouldn't make any difference but not four Fahrenheit Fahrenheit would be a different Delta T because the ticks are not the same size so to interconvert between those remember remember that Kelvin is equal to your degrees Celsius plus 273 this 273 is absent is hero Kelvin is negative 273 degrees Celsius so that's why you have to add 273 to your Celsius all the time so zero degrees Celsius is 273 and there it is zero degrees Celsius is 273 Kelvin and then a hundred degrees so this is the freezing point of water and this is the boiling point of water now remember water is the most common substance on the planet and that's why a lot of things are based on water so water is the standard here's a formula for Fahrenheit to Celsius and there's your markers for Fahrenheit is 32 degrees is freezing 212 is boiling now let's talk about scientific notation scientific notation is a way to write numbers that are really really big or really really small and they're written in such a way that you get down to here on this slide this is a really big number as abogados numbers there's a really small number mass of single carbon grams and to write a scientific notation you have a certain part here this is the number portion and then you multiply that number by 10 so many times or divided by 10 so many times here you would be multiplying this number by 10 so many times to get the trip number here you would be dividing by 10 so many times to get to this number so this when you write scientific notation that portion of scientific notation is a number between one and ten or nine point nine nine nine and that is a positive or a negative integer as I indicated up here so scientific notation if we put this and put these numbers into scientific notation this five sixty eight point seven six two becomes five point six eight seven six two times ten to the second so all of these numbers are significant so they should come down into the scientific notation number portion now if you have one that's smaller you move the decimal to the to the right and again this guy has three significant figures and that's why they all come to this spot now I moved it how many times to go to the right one two three four five six and that's where the negative six comes from right here so this number seven point seven two times ten the negative six has three significant figures so keep on going with significant figures now this is you pregnant beat to death with this over your career of education because significant figures are important in the fact that when you use measuring devices the number of significant figures that comes from a measuring device tells you how precise and therefore not accurate but it can be more accurate than other measuring devices that don't have as many significant figures so the number of significant figures in a measurement of course when you look at a number that is a measurement any digit that is not zero is significant for example all of these are significant and that means if this was this as a mass this balance here however you balance whatever balance you used is reading to the I mean this is kilogram so what would this be this would be one two three four grams but notice it's not point zero it's reading to the ones place is what this is reading to so this is not a very good balance but it's for very large you know so maybe that's why but either way it's reading to the one this place but it still has four significant figures because they're all nonzero zeros between nonzero digits are significant for example this has three significant figures this is part of the measurement zeros to the left of the first non-zero digit are not significant this only has one significant figure these are not significant so if you were to write this in scientific notation it would be 8 times 10 to the negative 2 and there's your one significant figure if a number is greater than one that all zeros to the right of the decimal point are significant for example two point zero is two significant figures it's a milligrams so was saying the balance we used was able to measure to the tenth of a milligram if it's less than one then only the zeroes that are at the end and in the middle of the number are significant for example these are not significant this one is so if you write this in scientific notation you would see it to be four point two zero times 10 to the negative third grams so there's your three significant figures so let's look at practice here how many significant figures are in each of the following since they're both non zero two for this one since the zeros are trapped in between two nonzero digits for this one is a decimal has zeros out front and a zero behind these are not significant but that one is three this one is already in scientific notation so also you going to do is look at this portion and that count the number of digits there and it is to this one this one is a whole number now this zero is not significant in this situation now we'll see a couple different things here and you say apparently the balance that I use to measure this mass was only read to the tens now what that means that this number has two significant figures but what if my balance like on the previous slide red to the ones now I can't put point zero because that means to the tenths but I can put a point here now this would have three significant figures and that point there means it's reading to the ones place now what do we do with significant figures when we add and subtract we have to carry the correct number of significant figures through our calculations how to do that with addition and subtraction when you're adding and subtracting decimal numbers you have to look at each of the individual numbers and then when you add and subtract the numbers you round your final answer to reflect the least precise answer now we've got to be careful with the words precision and accuracy we're going to talk about that a little bit more here a second but the more precise the number is the more decimals it has the more significant figures it has now when we're doing decimals these two situation here this has three after the decimal and only one after the decimal but when we add and subtract numbers we have to round the answer to the number now when we're doing decimals we only looked after the decimal so we have to round this number to one significant figure after the decimal because we couldn't round it to only two significant figures I mean we could but that would give 90 and then 90 point is has only two significant figures you lose a lot of information in there and you didn't need to lose because this did read to the tens place so we want to keep that for example of subtraction again looks like this guy has two after the decimal so that's the less less precise of the two for multiplication or division you look at the two numbers and see which one has the least number of significant figures and then you round it to reflect that one so this one has three significant figures this one has five so you could round this one to only three significant figures this one has two significant figures this one has so we round it to two this one has five round this one to two significant figures which would be 1:06 plain for exact numbers exact numbers our numbers from definitions are counted so an exact number for example if I was to do a calculation like this if I want to take the average of three numbers I divide it by three but you can't take the number of significant figures of this one it doesn't have significant it's just dividing it by three it's not one of the metric numbers so we would still add them together first and divide by three but we would still need to use the number of significant figures that was reflective of the measurements so let's talk about accuracy and precision you've probably seen this picture a thousand times I always tell you about this one is accurate and precise this one is precise but not accurate and this is neither accurate sighs but what does that really mean I mean accuracy is is as close as you can get to the true value precision of a set of measurements is how close they are to each other even if they are not accurate so if you don't know what the true value is you can never make decisions about accuracy precision on the other hand you can make decisions about and the more precise an instrument is for example the more precision a set of their measurements would reflect now I know that's not it kind of weird but let's let me give you an example if you have a measurement of one point one three five now I can say that's a pretty precise measurement it's precise in the fact that if I were to take if I were to take many measurements I might get something like one point one three seven one point one three eight whatever these are all pretty close to each other and notice that all the first three digits are the same so when you have instruments that are very that go out to many decimals like this that means that they are pretty darn precise and they will their set of measurements will be closer to each other now you would compare that if say I had a balance this balance measured to the thousands thousands place there's a balance in the lab that only measures to the hundreds and then you can have balances that only measure to the tenths so say I'm high a balance that measured to the tenths and I got one point one one time at one point three the next and one point for the next these are actually much further apart from each other and therefore less precise than this set is over here so precision for a set of measurements you can say well these are precise well compared to what I mean if these are more precise even though they're kind of the seen so precision for a set of measurements is how close to they are to each other a precise number usually means a number with more decimals because it was made with an instrument that had a higher precision accuracy you really have no idea accuracy you have to know when your instrument was less calibrated and was it calibrated with so accuracy is how close it is to the true value but precision is kind of thrown around so we just have to be aware of what that means and I drew over that there but accuracy is how close they are to a true value and precision is how close they are to each other now let's talk about dimensional analysis I know this lecture is getting a little bit long here but with dimensional analysis it's a way to dig yourself out of any hole of calculations using units now I know that sounds weird but it kind of makes life a little bit easier when you are doing calculations for chemistry or for physics or mathematics you want to have units the units give you information about the numbers and then also give you information about how you can manipulate those numbers to get a different value in a different unit a lot of times that's how people discover things especially physicists they discover the mass of the electron the charge on an electron things like that that was not by a direct measurement it was by inference and by dimensional analysis and mathematics so anyway also know what dimensional analysis is how would you do this type of problem you say how many milliliters are in 1.6 meters now if you know that there's a thousand milliliters and a liter you might know just to move this over three spaces and then you'd have sixteen thirty milliliters now I want you to notice three sig figs three sig figs I didn't change that but how would you do this as far as dimensional analysis is concerned dimensional analysis is a way to set up calculations in which you can cancel out units so if you look at this you can see that these are these would cancel out you were based in essence changing the unit from liters to milliliters now I want you to notice this is not correct because how can you know you sometimes you say should I divide by a thousand should I multiply by a thousand well it depends it depends on what your units tell you your units should line up in the fact that they should cancel each other like they did up here these cancel each other and left in milliliters these are not cancelling if you did a calculation like this your final unit is liter times leader is leader squared and then you would have liters per milliliter and that would be incorrect so you just got to be careful and if you make sure your units cancel properly a lot of times you don't even need to know the relationship if you say you forgot that D equals M over V you can still wing it if you knew what the units are and all the numbers and what unit you wanted to get to so something an example of that would be something like this where the speed of sound in air is about three hundred and forty three meters per second what is the speed in miles per hour now this is a conversion problem and a conversion problem is converting meters to miles and seconds to hours and almost all problems like that are kind of like conversion for so you see you start with your number here 343 m/s and what is this step doing and this is taking meters to miles and our second step is taking minutes seconds to minutes but notice you wanted minutes on the bottom and that's why you have this set up this way seconds and seconds and I'm taking minutes to hours on the bottom and then if you do your cancellation across the way here you meters cancel properly seconds cancel properly minutes cancel properly and your