Let's see how quickly we can cover everything you need to know for Cambridge International or CIE GCSE chemistry. This is good if you're doing separate or triple coordinated or combined. I'll tell you when something is just for coordinated and or triple. We're going to be really moving here, so pause the video if you need a bit more time to get your head around something you see. Let's go. Substances, stuff are made of atoms. The different types or elements of atoms there are are represented in the periodic table by a symbol. A compound is a substance that contains two or more different types of atoms chemically bonded together. For example, the chemical formula for water is H2O. It's made up of hydrogen and oxygen atoms. For every one oxygen atom, there are two hydrogen atoms. If there's no number after a symbol, there's an invisible one there. These atoms change what they're bonded to and how they're bonded through chemical reactions. We can represent a reaction with a word equation and a chemical equation using symbols. As atoms are not created or destroyed in any chemical reaction, there must be the same number of each type of atom on both sides. So sometimes we must balance equations. Pro tip, start balancing atoms that are only in compounds. So with this one, let's go with the carbons first. There's one on the left, one on the right. So that's all good. Hydrogen's, there are four on the left, only two on the right. Now, we can't change the small numbers because that would change what the compound is. So what we can do is put numbers in front of elements or compounds to multiply them up. Stick a two in front of the H2O. We now have 2 * 2 hydrogens's. So that's four. That's also doubled the oxygen's in it, however. So now we have four oxygen on the right. Still only two on the left. So doubling this O2 on the left takes care of that. If there's an element in a reaction like oxygen here, we always finish balancing that as there's no knock-on effect. A mixture is any combination of any different types of elements and compounds that aren't chemically bonded together. For example, air is a mixture of oxygen, nitrogen, and more. Solutions are mixtures too like salt water, a mixture of water and sodium chloride. You can separate large insoluble particles from a liquid using filtration like sand from water as sand can't dissolve. Crystallization can leave a solute that's the solid dissolved in a liquid behind after you evaporate the solvent from a solution like salt from water. Similarly, distillation involves heating the solution as well, but this time the gas is cooled so it condenses back into a liquid. You can also do this at different temperatures to separate the different liquids of a mixture as they will have different boiling points. This is called fractional distillation. These are all physical processes though and not chemical reactions because no new substances are being made. Obtaining pure substances is very important when it comes to chemistry. One way to tell if a substance is pure or not is by testing to see what its melting point or boiling point is. If it's pure, it should be a very specific temperature. A formulation is a mixture that has been specially designed to be useful in a very specific way with very specific quantities of different substances used to make things like paints, fuels, alloys, fertilizers. Think of George's Marvelous Medicine as being the ultimate formulation. Chromatography is a way of separating substances in a mixture. For example, pigments in inks or drugs in a urine sample. The stationary phase, often special chromatography paper or just filter paper, is what the substances move up with the help of the mobile phase, often just water, which rises up the paper due to capillary action, dragging lighter particles further up the stationary phase. We draw the line at the bottom in pencil so it doesn't move with the solvent, the water. Then at the end of the process, we measure how far the solvent has moved and also how far the substance or substances have moved too. And these are both measured from that starting line. We can then calculate an RF value. That stands for retention factor, which is just a ratio of how far a spot has moved compared to the solvent. So that ends up being a number between 0 and one. We can compare RF values of our spots with known RF values to identify what's in our mixture. Solid, liquid, and gas are the three main states of matter. For example, water can be ice, a solid where the particles or molecules in this case vibrate around fixed positions. It can also be liquid water where the molecules are still touching but are free to move past each other. And it can also be a gas, water vapor we call it when it's water, where the particles are far apart and move randomly and they also have the most energy and so move quickly. As molecules in a gas are far apart, gases can be compressed while solids and liquids cannot. To melt or evaporate a substance, you must supply energy, usually in the form of heat, to overcome the electrostatic forces of attraction between the particles. We don't say we're breaking bonds in this case. Note that none of these make a new substance. So these have to be physical changes again, not chemical reactions. We're not breaking any chemical bonds. In chemical reaction equations, we indicate what state a substance is in with state symbols. Brackets S for solid, L for liquid, G for gas, and also AQ for aquous. That means dissolved or insolution. Again, like salt in water. The idea of what atoms are like came about gradually. JJ Thompson discovered that atoms are made up of positive and negative charges. He came up with the plum pudding model of the atom. A positive charge with lots of little electrons dotted around it. It was Ernest Rutherford who found that the positive charge must actually be incredibly small. We now call this the nucleus and the electrons must orbit relatively far away from it. He discovered this by finding that most alpha particles fired at a thin leaf of gold atoms went straight through proving that atoms must be mostly empty space. Neils Boore later discovered that electrons exist in shells or orbitals. Then James Chadwick discovered that the nucleus must also contain some neutral charges. He called them neutrons while the positive charges are called protons. Protons and electrons have equal and opposite charges. So we just say they're + one and minus1 relatively speaking. Neutrons have a charge of zero. Protons and neutrons have essentially the same mass, so we say they have a relative mass of one. Electrons are very light in comparison, so we say they have a mass of zero or just very small depending on the situation. The periodic table tells us everything we need to know about an atom. The bottom number is the atomic number. That's the number of protons in the nucleus. This is what determines what elements you have. Every atom has an overall neutral charge. So that means they must have the same number of electrons as protons. If an atom gains or loses electrons, it's now called an ion, not an atom. The top number is the mass number or relative atomic mass or ram for short. It tells you how many protons and neutrons are in the nucleus. So that must mean that this carbon atom, carbon 12, has six neutrons on top of its six protons to make that 12. However, you can get a carbon atom with seven neutrons instead. So its relative mass is 13. These are what we call isotopes. Atoms of the same element, but different numbers of neutrons. You might see a number that isn't a whole number for the mass. This is because periodic tables sometimes show the average mass for all of the isotopes of that element found in the world. For example, if you have some chlorine gas, it turns out that 75% of the atoms will have a mass of 35, while 25% of the atoms will be 37. These are what we call their relative abundance. To find the average, we just pretend that we have 100 atoms. We add up the total masses of all the isotopes, then just divide by 100. That's why chlorine's average relative atomic mass is 35.5. Like we said, electrons exist in shells around the nucleus. The shells fill up from the inside with a maximum of two on the first shell, eight on the second and third shells. Then we only go to two on the fourth shell. That's 20 electrons altogether which brings us to a calcium atom. After this we get into the transition metals where things get a little bit crazy. So we leave that until a level chemistry. So we only care about the electron configuration going up to 2882. Magnesium has 12 electrons. So its electron configuration for example would be 282. The modern periodic table can be split up into different sections. For example, everything to the left of this staircase is called a metal. Metal atoms always donate electrons to gain an empty outer shell of electrons. Again, slightly weird with transition metals, but we don't think about their shells. To the right of the staircase, non-metals. They always accept electrons to gain a full outer shell. The column an atom is in is called the group. It tells you how many electrons an atom has in its outer shell. Again, the transition metals work in a really weird way, so they don't get their own group. In fact, it turns out this is because they can donate a different number of electrons when they bond to different things. The atoms in group one are called the alkalion metals. They all have one electron in their outer shell which they give away, donate when they bond to something. So they have similar properties like when they react with water. The further down the group you go though, the further that outer electron is from the nucleus. So the electrostatic attraction is weaker between the negative electron and the positive nucleus. This means that the electron is more readily donated. This means the metals get more reactive as you go down the group. Group seven are what we call the hallogens. They're essentially the opposite. They have seven electrons in their outer shell. So, they need one more to gain a full outer shell. The further down the group you go, the less readily an electron is accepted onto that shell that's further away from the nucleus. So, they get less reactive down the group. Their boiling points also increase down the group too. Group zero, sometimes referred to as group eight, are called the noble gases. They already have an empty or full outer shell. Just depends on your perspective. So, they don't react. In reality, they can react under special conditions. So, we just say they're very unreactive. We don't really say group eight anymore, though, because some people thought that helium might feel a little left out as it only has two electrons in it outer shell. As electrons are negative themselves, metals become positively charged when they lose them. They always form positive ions. All of group one lose one electron when they turn into an ion. So, all of their ions are one plus, but again, we don't write the one, we just put plus. Group two lose two electrons to get an empty outer shell. So their ions are all two plus. Group seven gain one electron each. So all their ions are minus. Group six's ions are all 2 minus. The atoms in group three, four, and five don't really form ions except for aluminium, which is 3+. Like we said, transition metals can donate different numbers of electrons. For example, an iron ion can be Fe2+ or Fe3+. It can donate two or three electrons. So we give them the names iron 2 and iron 3 to distinguish between them. Transition metals are generally harder and less reactive than the alkalion metals. They also form colored compounds. Metal atoms bond to each other through metallic bonding. Essentially a latis or grid of ions is formed with a sea of deoized electrons around them. Deoized just means they're not exactly on the atom. As these electrons are free to move, metals make good conductors of electricity and heat. Metals bond to non-metals through ionic bonding. Like we said, a group one metal needs to lose an electron while a group seven atom needs to gain one. It's a match made in heaven. For example, a lithium atom donates or loans its outer electron to the chlorine. We can draw a dotted cross diagram to show where the electrons end up. You can choose which one belongs to which. We only need to draw the outer shell for each. Don't forget to put brackets and the charge of the ions. When it comes to ionic bonding, the charges of all ions in an ionic compound must add up to zero. So, Li plus and Cl minus is all good. So, this is the chemical formula for it. Same with burillium oxide, B2+ and O2 minus. Burillium chloride on the other hand, well, the burillium needs to lose two electrons while a chlorine only needs one. So, that means there must be two chlorines or chloride ions for every burillium. So, B2+ and two lots of Cl minus adds up to zero. So that means the chemical formula is be sorted. Ionic compounds consist of lots of repeating units of these ions in a lattice to form a crystal. They have high melting points and boiling points due to the strong electrostatic forces that need to be overcome. And they can conduct electricity but only in liquid form that is molten or when dissolved in solution. That's because the ions are free to move in both cases and they carry charge. You can also get molecular ions. For example, O minus is a hydroxide ion and consists of a hydrogen atom and an oxygen atom. So, magnesium would need two of these to make magnesium hydroxide. Here are a few other examples. By the way, I spell sulfate with a PH instead of an F because I'm stubborn and refuse to adopt the American spelling. You'll get the mark either way. Any ionic compound can be called a salt, not only sodium chloride, your table salt. The name is always the metal ion, positive ion or cation we can call it, followed by the non-metal ion or anion. Annion names are different from their normal names. Like we've just seen, it's not sodium chlorine but sodium chloride. Some people remember which way around cations ions and annions are by liking cats and they say cations ions are positive. Non-metals bond to each other with covealent bonding to form molecules. They do this by sharing electrons to gain full outer shells. For example, chlorine gas is Cl2. Each chlorine atom shares an electron with the other, so they're both happy. Never write down happy in the exam, though. Here's the dots and cross diagram. We can also draw the structural formula for molecules with just symbols and lines. We can also say that every one of these represents a dot cross electron pair. Each oxygen needs two extra electrons. So, O2 is a result of each oxygen atom sharing two electrons each. As such, this is a double covealent bond. Nitrogen N2 is one of the few molecules with a triple bond in. In coalent bonding, the number of electrons an atom needs is the same as the number of bonds it must make. Hydrogen can only ever make one bond. Carbon makes four bonds, etc. Here's a few more. If you're not in a rush, pause the video and have a go at them. And here are the answers. These above are what we call simple molecular or simple covealent structures. Individual molecules that can all mix together. These have relatively low boiling points as there are only weak intermolecular forces between them that need to be overcome with heating. Be careful though that's not covealent bonds being broken like we said and unlike ionic compounds these can't conduct electricity even as liquids. Giant covealent bonding is similar to the latis nature of ionic compounds. Atoms form covealent bonds to other atoms which form bonds to other atoms and so on until what we have in effect is one giant molecule. Diamond is an example of this. It's a crystal of carbon atoms bonded to each other. That's why it's so hard and has such a high melting point. You would have to break the covealent bonds in order to do that and they're incredibly strong. Graphite is only made of carbon as well, but it's not diamond. So, it's an allotrope of carbon made out of the same atoms bonded together in a different way. Graphite consists of layers of carbons with three bonds each in a hexagonal structure. Where's the fourth bond though? Well, the spare deoized electrons form special weak bonds between the layers, which means that it can conduct electricity cuz the electrons can move between the layers as well. And it also means the layers can slide over each other easily, which is why it's used in pencils. As a side note, metal alloys are stronger than pure metals. Having mixtures of metals means that we have different size atoms and that disrupts the regular latis so layers can't slide over each other as easily. Back to carbon allotropes. Graphine is just a single layer of graphite. Ferines are 3D structures of carbon atoms. For example, Buckminster ferine is a spherical football-like structure consisting of 60 carbon atoms each. Ferines that have a tube shape are called nano tubes. Just for triple real quick, nanoparticles is the term given to structures that are between 100 and 2,500 nmters in size. Whereas particles bigger than this are called coarse particles like dust. Surface to volume ratio is just one divided by the other. If the length of a side of a cube doubles, that means this ratio halves. As nanop particles are tiny, this ratio is huge for them, which means that fewer could be needed to fulfill a purpose compared to larger ones. Total mass of all substances is conserved in a chemical reaction. Like we said earlier, that must mean the atoms that go in must come out. So, we must balance equations to that end. We already know about relative atomic mass, but if it's a compound, we can add these up to give the relative formula mass. We just add up the individual rams. So CO2 is 12 plus 2 lots of 16. So that's 44. Some reactions produce a gas product which if it leaves the reaction vessel will result in a seeming decrease in mass of the reactants. A mole is just a specific number of atoms or molecules. But we don't really need to know the number. It's just a way of comparing amounts of substances as we can't deal in individual numbers of atoms or molecules. If you're foundation, you don't need to deal in moles. By the way, if you have as many grams of a substance as its relative atomic or formula mass, you have one mole. So, one mole of carbon has a mass of 12 g. That means we calculate the number of moles of something we have like this. Moles equals g over g, where grams is short for relative atomic mass, but it also could be relative formula mass. This is an equation worth remembering. Let's take our methane combustion reaction from earlier. Like we said, in order to balance this, we'd need two oxygen molecules per one molecule of methane. This is also true for moles, too. Then we'd need double the moles of oxygen to methane. So, here's how a question could go. How many g of water would be made if 64 g of methane reacted completely with oxygen? We need to get from the mass of one thing to the mass of another. So, we use moles as the middleman. The process is this. Mass, moles, moles, mass. We switch from one to the other at the halfway mark. So, a mass of 64 g of methane. How many moles is that? Moles equals g over g. So, that's 64 / 16. That's four moles of methane. But look, there's no number in front of the methane, but there is a two in front of the water, which means we must have double the moles of water. So, that's 8 moles. By the way, we can say that the stochometry is 1:2. That just means the ratio of moles of one substance to another in a reaction. So, all we have to do then is turn that back into mass using our equation by rearranging it. Put it into a triangle if you have to and cover up mass. G equals moles time g. So, that's 8 moles* w of 18. That's 144 g of water made. You could also be given the mass in kilog or even tons. The great thing is is that because this is all relative, we can just put those masses into our equation instead of g. And so long as you stick with that unit for the whole question, you'll still end up with the right answer. Of course, we can also use moles to predict how much of a reactant we would need in a reaction. As you can see, we need two moles of oxygen to every one mole of methane. If we had that one mole of methane, but only one mole of oxygen, that means that not all of the methane would react. Some would be left behind. We say that the oxygen is the limiting reactant. In this case, it ran out first. The concentration of solutions can be given in g per decime cubed, where a decime cubed is 1,00 cm cubed. But it's often useful to convert this into moles per decime cubed instead. If one mole of HCl is dissolved in 1 decime cubed of water, we've made hydrochloric acid at a concentration of 1 mole per decime cubed. Sometimes we shorten this to just one molar. We saw briefly earlier that metals vary in their reactivity as some donate their electrons more readily than others. Here's the reactivity series for the most common metals we consider. You can see that hydrogen and carbon have also snuck in there. That's because it's often necessary to compare the reactivity of metals to those in order to predict what will happen in a reaction. A more reactive metal will displace a less reactive metal from a compound. That is, kick it out. For example, if you place zinc in copper sulfate solution, you'll see copper forming on the lump of zinc. The zinc displaces the copper to form zinc sulfate, kicking the copper out of the compound. We know that alkalion metals react with water. The reaction happens because, for example, potassium is more reactive than hydrogen. So in essence it displaces it from the water leaving potassium hydroxide and hydrogen gas is produced. We can use this when it comes to extracting metals from their ores found in the ground. Any metal less reactive than carbon can be displaced by it. For example, iron can be displaced from iron oxide with carbon. This is called smelting. We can also say that the iron oxide has been reduced. It's the opposite of oxidation because oxygen is lost. Even if oxygen is not involved in a reaction, we can still say that reduction and oxidation happen depending on whether a reactant loses or gains electrons. The pneummonic is oil rig. Oxidation is loss, reduction is gain of electrons. That is the iron ions in the iron oxide are positive, of course, cuz they're metals and they gain electrons to turn back into atoms. They become neutral. They've been reduced. Here's the half or ionic equation for this. We should never really have a minus in any half equation. So think carefully about which side the electron should go on depending on whether it's oxidation or reduction. Metals more reactive than hydrogen can displace it from an acid. So most metals react with hydrochloric acid and sulfuric acid for example. This produces a salt. Alkalies they have a pH greater than 7 react with acids less than 7 to produce a salt and water. If the quantities used are correct according to this stochometry, they will neutralize each other completely to leave no unused reactants. Here's an example. Sodium hydroxide and hydrochloric acid makes sodium chloride and water neutral pH of 7. If sulfuric acid is used, a metal sulfate is made. Nitric acid metal nitrate. These salts are left in solution that is dissolved in water. When any substance dissolves, its ions partially dissociate as does the water actually into H+ and O minus ions. We can obtain solid crystals of a dissolved salt by warming gently so the water evaporates. The pH scale is a logarithmic scale base 10. It's not linear. What does that mean? Well, an acid contains H+ ions. And an acid that has a pH of three will have 10 times the concentration of these compared to an acid of pH4. PH3 would have 100 times the concentration of H+ ions compared to an acid of PH5 and so on. Alkalies work in a similar way but with O minus ions instead. The higher you go the greater the concentration. A strong acid is one that dissociates or ionizes completely when in solution like hydrochloric, nitric and sulfuric acids. Weak acids on the other hand only partially dissociate like ethaninoic, citric and carbonic acids. The pH of an acid depends on both its strength and concentration. If hydrochloric acid and ethaninoic acid have the same concentration, the hydrochloric acid will have the lower pH as it's stronger. If you melt an ionic compound, let's say aluminium oxide, it can conduct electricity as the ions can move. We know that from earlier. By passing a current through it using inert electrodes, that means they won't react like carbon. the positive metal ions or cations Al3+ in this case. They move to the negatively charged electrode. We call that the cathode where they receive electrons and turn into atoms. Cations are always reduced at the cathode. So in this case solid aluminium is formed on the cathode. The negative ions or annions O2 minus in this case move to the positive electrode the anode where they lose electrons. In this case oxygen gas O2 is formed. Annions are always oxidized at the anode. This is one way of purifying metals or extracting them from compounds. Say if displacing with carbon isn't an option due to their reactivity. In this case of aluminium oxide, the oxygen produced at the graphite carbon anode reacts with the anode itself. So these need to be replaced every so often. Again, specifically for this case, aluminium oxide is mixed with kryolyte to reduce its melting point, making it cheaper to extract the aluminium. We can also do electrolysis with ionic substances in solution. Say sodium chloride solution. We know that the solution is a mixture of Na+, Cl minus, H+ and O minus ions as they're all partially dissociated. But what will be attracted to and reduced at the cathode? The Na+ or the H+? Well, it comes back to reactivity. The more reactive ion stays in solution while the less reactive one moves to the electrode. That's the H+ in this case. That's why hydrogen gas is made of the cathode here. If the metal is less reactive than hydrogen, say copper in copper sulfate solution, it forms on the cathode instead and the H+ ions stay in solution that actually makes an acid. If there is a halide ion present, like the Cl minus here, it is oxidized at the anode. If there's no halid ion in solution, the oxygen from the O minus is oxidized instead and oxygen gas is produced. Any chemical reaction involves energy transfers as energy is needed to break chemical bonds. While energy is released when chemical bonds form. Both of these happen in any reaction. If there is more energy released from bonds made than energy needed to break bonds, we say this is a net energy released and we should observe an increase in temperature as a result. This is an exothermic reaction. For example, combustion. The way I think about it is explosions are exothermic. I mean the X just means out. If it's the other way round, there is net energy input into the reaction. So, the reaction should get colder. This is an endothermic reaction. The practical on this goes as follows. We carry out a neutralization reaction between an acid and alkali in a polyyrene cup which is well insulated and a thermometer poked through a lid that sits on top. We measure the maximum temperature the reaction reaches. Then increase the volume of alkali used and repeat. Eventually, the maximum temperature will not get any higher due to all of the acid reacting. And the same amount of energy released is being shared across a larger volume of liquid. We can draw two lines of best fit for the rise and fall in these max temperatures where they meet tells us how much of the alkali was needed to neutralize the acid. We can use an energy profile to help us visualize the difference in energies between the reactants and the products. Now, this is something that people get confused with. The yaxis is potential energy. And you should know that usually in science potential energy and kinetic energy do a balancing act. If one goes down, the other one goes up. So if the potential energy of the products is less than the reactants, they must have gained kinetic energy and that always means a hotter temperature. This is an exothermic reaction. It might seem like the energy has gone down, but kinetic energy has increased. Of course, fuel must need a spark to start it burning, which is why we draw this bump to represent the activation energy, the energy needed to get the reaction started. Here's an energy profile for an endothermic reaction, too. Every bond needs a very specific amount of energy to break. For example, a carbon hydrogen covealent bond needs 413 kJ for every mole of these to break them. If a mole of these are made, it's the same amount of energy released. So, let's take our combustion of methane equation one last time and draw the structures so we can see all the bonds. We need to break all of the bonds in the reactants first. So, that's four lots of 413 and two lots of 495 for the two lots of oxygen double bonds. So, that's 2,642 kg per mole needed to break all of the bonds. The unit isn't that important, by the way. We're more interested in the numbers. making bonds. On the other side, 2 * 799 is released when the CO2 double bonds are made. Plus 4 lots of 467 for the two water molecules. That's 3,466 kJ per mole released. By the way, you'll always be given these numbers. You don't need to remember them. More energy is released than goes in in this case. So, it's exothermic. That checks out, doesn't it, of one minus the other gives us the net energy released. And in this case, that's 824 kJ per mole. We can test for hydrogen by holding a burning splint over the test tube which will produce a squeaky pop. Oxygen will relight a glowing splint. So carbon dioxide will turn lime water cloudy when bubbled through it. Chlorine gas will bleach damp blue litmus paper. That means turn it white. By we can test for some metals with flame tests. Lithium will produce a crimson flame. Sodium yellow, potassium lilac, calcium orange red and copper green. We can test for other metals in solutions by adding sodium hydroxide. Aluminium, calcium and magnesium in solution will produce a white precipitate. However, the aluminium hydroxide produced will then dissolve if excess sodium hydroxide is added. Copper 2 ions that is Cu2 plus ions form a blue precipitate. Iron 2 green precipitate ion 3 brown. You might have to complete an ionic equation for these. For example, the copper and hydroxide ions making copper hydroxide. And you got to make sure it's balanced, too. Just three quick ones. Carbonates react with acids to make carbon dioxide gas and we know how to test for that. We test for halalley ions that's halogen ions by mixing with silver nitrate solution and nitric acid. If chlorine ions are present, silver chloride is made. That's a white precipitate. Silver broomemide is cream and silver iodide is yellow. Finally, sulfate ions will produce a white precipitate when mixed with barryium chloride and hydrochloric acid. Titrations are only for triple. This is how we deduce the concentration of an acid or an alkali. We use a glass pipette to measure out a known volume of alkali and put it in a conicle flask with a few drops of an indicator like methile orange. We put the acid of unknown concentration in a boret above the flask. We open the tap and let it drip into the flask slowly while we swirl it. When it turns pink, we close the tap and if it stays pink after we swirl it, that shows that neutralization has occurred. You can also do a rough titration to get a rough value for the volume needed to do this. then do another and then add a drop at a time near the end point to get a more accurate value. Let's say that it's sodium hydroxide and sulfuric acid. Here's the balanced equation. So let's say that we had 50 cm cubed of 0.2 moles per decime cub sodium hydroxide. First we need to turn that volume into decime cub. So we divide by 1,000. So that's 0.05 decime cubed of the alkali. To multiply that by the concentration and we get 0.01 01 moles. From the stochometry of 1 to two for the acid and alkali, we can see that we need half the number of moles of acid to neutralize it. So that's 0.005 moles of acid needed. Now we can use our actual volume of acid measures, which finally we just calculate the concentration by doing moles divided by volume. That's 0.005 / 0.125 decime cubed. That's how we converted it. Which gives us a concentration of 0.4 moles per decime cubed. Don't forget that units are your friends if you forget what calculation you're supposed to do. In many reactions, we want to make as much product as possible. More often than not, though, there will be some reactants left behind over at the end. Like we know, for example, if a reaction is reversible, like the harbor process to make ammonium or about that in paper two, you'll always end up with hydrogen and nitrogen at the end. In this case, when it's reached equilibrium. Percentage yield merely tells you how much product is actually made compared to how much you could have made in theory had all the reactants reacted. For example, if you start with 20 g of reactants here, but only end up with 10 g of ammonia, the percentage yield is 50%. You must be given the actual masses involved in questions on this. So you can't predict what the yield would be just from the equation. How quickly a reaction happens is called the rate of reaction. Any rate is the change in a quantity divided by time. In this case, that something can be the quantity of reactant used or product formed. This quantity could be mass or volume of gas that's usually made. Anyway, they like to stipulate that this technically gives you the mean rate as the rate could be changing over the time you measure, but that's true for any measurement over time ever. So, that's a bit redundant, but we'll go with it for now. An experiment on this could be reacting hydrochloric acid and sodium thioulfate in a conicle flask sitting over a piece of paper with a cross on. As the reaction continues, the product form turns the solution cloudy. We say that's increased turbidity. We stop the timer when we can no longer see the cross from above the flask. Repeat this at different temperatures and you should see that the hotter the temperature, the less time it takes. Another potential experiment is measuring the volume of gas produced by using a gas syringe that fills up when connected to the reaction vessel. A graph to show this would have the quantity on the y-axis and time on the x-axis. It's usually a curve that starts off steeply but then levels out or plateaus which shows that the reaction has completed or we can say reached its end point. To find the rate at any time, you draw a tangent at that point. Pro tip, turn the page so you're drawing the tangent horizontally. That will help you draw it accurately. Then like the equation says, you can take the change in quantity and divide by time up divided by across. The rate of a reaction can be increased by the following. Increasing the concentration of reactants that are in solution. increasing the pressure of gas reactants and increasing the surface area of solid reactants that is crushing into a powder. Now, these three all have this effect because the reacting particles collide more frequently. They come across each other more often. Increasing temperature does that too due to the particles moving more quickly. But there's the added bonus that they also collide with more energy, meaning they're more likely to react when they collide due to activation energy. Remember your energy diagrams from paper one. Finally, adding a catalyst also increases rate as it reduces the activation energy needed. So, particles are more likely to collide successfully and react. Of course, any catalyst is not used up in a reaction. It is not a reactant or product itself. Reversible reactions are pretty self-explanatory. Once the products are made, they're able to return to their original reactants. The prime example here is the harbor process. Hydrogen and nitrogen react to make ammonia, which can also break down back into the separate gases again. More on what ammonia is used for later. In a closed system, that is no particles or energy going in or out, or both reactions will continually take place. Eventually, the quantity of particles on both sides will reach a point at which the rates of both the forward and reverse reaction will be the same. So that means there will be no more overall change in the quantities on both sides. Remember, that's not saying that the reaction has stopped per se. It's just that there's no more overall change. That is until a condition is changed which will affect these rates. Lhatalier's principle states if a system at equilibrium is subjected to a change, the system will adjust to counteract that change. Sounds awfully vague. So let's see what that means in practice. There are a greater number of moles on the left than the right of this reaction, which means that the reactants take up more space. Therefore, if you increase the pressure of all of these gases, we say this favors the forward reaction. That is the rate of the forward reaction will increase until equilibrium is once again reached. But that will happen when there's a greater proportion of ammonia than there was before. We could also say that the position of equilibrium is shifted to the right. Reducing the pressure would of course do the opposite by shifting it to the left instead. Concentration follows the same principle when it comes to solutions. by the way is naturally if you remove molecules from one side of the reaction the position of equilibrium shifts in that direction so more is produced increasing the temperature in essence means it's harder for a reaction to produce heat that means that a hotter temperature favors the endothermic reaction in this case that's the reverse reaction you can also think of it like this an endothermic reaction requires energy being put in so a higher temperature supplies that a colder temperature will favor the exo themic reaction. In this case, that's the forward reaction. As a rule of thumb, any reaction that involves the breaking down of one reactant, ammonia in this case, that's going to be endothermic. In any reversible reaction, if the forward reaction is exothermic, the reverse reaction must be endothermic and vice versa. Like we saw at the start, the harbor process is used to make ammonia, which can be used for fertilizers. Nitrogen can be easily taken from the air, whereas hydrogen can be obtained from electrolying water. The gases are passed over a catalyst at around 450° C and a pressure of 200 atmospheres. Like we saw with Lhatellier, a high pressure favors the forward reaction. However, we can't have too low a temperature, otherwise the rate of reaction will be too slow. So that 450° is a compromise to balance yield and rate of reaction. The ammonia produced is removed and the unreacted nitrogen and hydrogen are recycled, ready to make more ammonia. Plants need nitrogen to grow, which is why we use ammonia and fertilizers. But they also need phosphorus and potassium. Therefore, many fertilizers are NPK fertilizers. The ammonia is first used to make ammonium salts to go in the fertilizer. Potassium chloride and potassium sulfate are obtained by mining as is phosphate rock which needs to be treated with an acid first to produce a salt before going into the fertilizer. Polymers can be high density or low density. For example, you might see HDPE or LDP on plastics. They stand for high and low density polyethine. The difference depends on the conditions used when making them. Thermosoftening polymers melt when heated whereas thermosetting polymers do not melt no matter how hot they get. The difference is that there are these cross links between the polymer chains that are formed when a thermos setting plastic is made. That increases the forces between them holding them together. Alloys are mixtures of different metals. Bronze is an alloy of copper and tin, brass, copper, and zinc. Even gold jewelry isn't usually pure gold. it would be too soft. It's combined with silver, copper, and zinc. 24 karat is 100% gold. 18 karat being 75% etc. Steel is an alloy of iron and carbon which makes it stronger than pure iron if it contains chromium or nickel. It's a stainless steel which is more resistant to corrosion. Alloys are usually stronger than pure metals because the different size atoms disrupt the regular latis which means the layers cannot slide over each other as easily. Aluminium is used in an alloy when we need a low density. Corrosion is when materials are destroyed slowly over time by chemical reactions. For example, iron and steel rust when the iron reacts with oxygen and water. Other metals corrode in a similar fashion like the copper statue of liberty, now green copper oxide on the outside. We just reserve the term rust exclusively for iron. We can coat a metal with a more reactive metal that corros before the other. We then call that a sacrificial metal. Zinc is an example. Coating a sheet of another metal with this is called galvanizing. algorithm. Composition of gases in the atmosphere has changed over the course of the Earth's history. Of course, records only go so far, so we have to extrapolate to get an idea of what it used to be like, but as per usual, historical science can't be tested. So, it's pretty much just a good guess. To begin with, it would have just been a lot of nitrogen and carbon dioxide. This then probably dissolved into the oceans, which were themselves probably a result of water vapor from volcanoes condensing. And the this carbon dioxide could have then been trapped in sediment, rocks, and fossil fuels, reducing the carbon dioxide in the atmosphere. Algae and plants turn CO2 into oxygen through photosynthesis, reducing the levels of CO2 to 0.018%, which is what we have today. Water vapor, carbon dioxide, and methane absorb longer wavelength radiation and keep the earth warm. Without them, we'd freeze. This is the greenhouse effect. CO2 levels have increased since the industrial revolution, which some think is responsible for the increase in global temperatures, as these are such complex systems that it's incredibly hard to model them. I'm old enough to remember when the term carbon footprint entered the mainstream in the mid-200s when everybody went mad for it. The idea that everything you do is responsible for carbon dioxide being released into the atmosphere and that we should reduce that or offset it by planting trees, for example. Carbon dioxide is an atmospheric pollutant. It binds to your red blood cells, so less oxygen can be transported around your body. It's also odorless and colorless, so it's hard to detect. That can prove fatal. Most fossil fuels release sulfur dioxide when burnt, which causes acid rain. Nitrogen oxide can also be released, which can cause breathing problems. Soots is just particulates of carbon made from incomplete combustion, which can also cause health issues. If you're like me, you probably take clean drinking water for granted, but many people around the world don't have that. Portable water is what we call water that has low enough levels of salt and microbes that it's safe to drink. In most countries, water is taken from a fresh water source, so little salt is dissolved in it. It's passed through filter beds to remove large insoluble particles, then sterilized to kill microbes, usually using chlorine, but we can also use ozone or UV light. In some countries, there are few or no freshwater sources, so they must get seaater and remove the salt. This is called dissalination which can be done through distillation but also by using special membranes that employ reverse osmosis. However, both of these require a huge amount of energy. Portable water isn't pure water of course. In fact, pure or distilled water is dangerous to drink in large amounts as there being nothing dissolved in it. Water will move into your cells due to osmosis and then become turgid. Organic compounds are those that have carbon forming the backbone of the molecules. Crude oil can be found underground and is the result of plankton being buried under water a long time ago. It consists of mostly hydrocarbons that is molecules only made up of carbon and hydrogen atoms. Most of these are alkanes which are chains of single covealently bonded carbon atoms surrounded by hydrogen atoms. As such there's always twice as many hydrogens as carbons in a molecule plus another two on the ends. We can therefore write a general formula for alkanes CN and then H2N +2. All alkan names end with a whereas the beginning of the name tells you how long the carbon chain length is. Meth is 1, E is 2, propus 3, but 4, pentis 5, hexis 6 and so on. Crude oil isn't useful as a mixture of all of these different length alkanes. So we use fractional distillation to separate them out. We heat them so they evaporate and rise up the fractionating column. Apart from the very longest ones which stay as liquid, generally used as buimmen on roads, the column gets cooler the higher up the gases rise. As different length alkanes have different boiling points, they condense back into liquids at different heights where they're then collected. Longer alkanes have higher boiling points because there are stronger intermolecular forces between them which more energy is needed to overcome. The shortest alkanes remain as a gas even at the top. We call this fraction LPG or liquid petroleum gases because they're put into pressurized containers afterwards to transport and they're turned into liquid. LPG contains a range of chain length alkanes like all of the fractions below. In LPG's case, it's up to four carbons long. These are the other fractions you need to know. Petrol is the next longest fraction. So, it condenses just below LPG. That's used in cars, of course. Kerosene is used for jet fuel. Then, diesel oil, cars and lries and things. And heavy fuel oil is used in large ships. It's back into liquid. As you can see, these alkanes can be burned as fuel. You should remember that complete combustion with oxygen produces carbon dioxide and water. You know about their varying boiling points, but you also need to know that longer fractions are more viscous or have higher viscosity. It's just a sciency word for more thick and gloopy. And shorter fractions are more flammable, easy to burn. But these different fractions can also be used to make solvents, lubricants, detergents, and perhaps most importantly, polymers used for plastics. Polymers can be made from alkenes, but not alkanes. An alken is a hydrocarbon that has a carbonarbon double bond in. By the way, we can call this C double bond C a functional group. Because of this double bond, we can also say that this molecule is unsaturated, whereas alkanes are saturated, which essentially means that they're full. But that's why you can test for an alken which is a colorless liquid by adding bromine water which is orange. If the mixture turns colorless that means that the bromine has bonded to the alken. For example, it bonds to ethine by breaking that double bond into single bonds used to attach the broines. The proper name of this product by the way is one two dybrmo ethane. And this is saturated as you can hopefully see. This cannot happen with an alkan as it's already saturated of course so it stays orange. Chlorine and iodine react in a similar way. And water can also saturate an alken by attaching itself as an H and an O functional group. We've now made an alcohol. By the way, more on this for triple in a bit. Now, there are two more problems with crude oil. One is that the demand for shorter alkanes is much higher than that for longer ones. Also, there aren't enough alkenes in it for our purposes. Cracking solves both of these problems. that is breaking apart a longer alkan into a shorter alkan and an alkan. Catalytic cracking requires a temperature of around 550° C and a catalyst called a zeolyte. If there's no catalyst, you can just use an even higher temperature of over 800°, which makes sense, doesn't it? This is called steam cracking. Let's take butane and crack it. It can split right down the middle, but there must be the same number of all atoms in the product. That means that yes, we make ethane, but there's not enough hydrogen to make another ethane. So instead, it makes ethane as well, the alkine, which of course is then useful for making polymers. It could also split here instead to make methane and propane. Cracking allows us to meet the demands for shorter alkanes for fuels as well as produce alkenes for making other materials. More on polymerization for triple in a bit. The rest of organic is just for triple, so skip to chemical analysis if you're doing double. Like we mentioned earlier, an alcohol is an organic compound with an O functional group. Their names always end with. So this is ethanol. These can react with oxygen that is combust to make carbon dioxide and water if it's complete combustion and carbon monoxide or carbon and water if it's incomplete combustion when there's less oxygen available. Reacting ethanol with sodium makes sodium ethoxide and hydrogen. Similarly for propanol and butinol, just one of those random bits you need to know. Short alcohols like these can mix with water to produce a solution which gets more difficult as they get longer. When an alcohol is oxidized without combustion, that is with an oxidizing agent, it makes a caroxyic acid. That's a molecule with instead of CO, it's CO. That's the functional group. It still has the hydroxide, the O group, but it's not an alcohol anymore. The name of this would be ethaninoic acid. We can also get propinoic, butyricininoic acid, etc. Polymers are super long chain alkanes made up of repeating sections made from monomers. Poly just means lots. Mono just means one. For example, lots of ethines, the monomer, can be joined together through addition polymerization to make polyethene or polyine. That's the polymer. These monomers must have a double bonding. Note that even though it makes a long alkan, we still use the name of the alken it's made from. It's polyethine, not polyethane. As you can see, this happens because the double bond splits. So, a carbon can bond to the next monomer and so on. Thankfully, we only have to draw the repeating unit with brackets around it and the bonds coming out with an N on the outside, showing that there are lots of these joined together. Condensation polymerization is when we join together two monomers that have two functional groups. For example, an alcohol and a caroxyic acid. First, let's look at the reaction between ethanol and ethaninoic acid. These can react to produce ethile ethaninoate. This is an esther. Can you see water must also be produced. Now let's react an alcohol with an O on both ends and a caroxyic acid with CO on both ends too. Now this reaction happens on both ends and we can make a chain of this esther. This would then be a polyester. It doesn't matter what's in between the functional groups. We can sometimes just write R as a shorthand for the stuff in the middle or just a wee box. The process is the same every time. Again, water is chucked out. Hence why it's called condensation polymerization. Cells or batteries, they contain chemicals that can produce a potential difference of voltage to power electrical appliances. The basic composition is two different metals in contact with an electrolyte. Non-renewable batteries stop working when the reactants are used up. Rechargeable batteries can be recharged when a supplied current causes the reverse reaction to occur. Hydrogen fuel cells work in a similar way. Water is split up into hydrogen and oxygen by electrolysis. When they recombine, a voltage is produced. That's it. Hope you found that helpful. Leave a like if you did. Pop any questions or comments below. And hey, after you've done the exam, why don't you come back here and tell us how you found it? We'd love to know.