foreign [Applause] [Music] IGCSE chemistry video and I'm going to be talking through my top tips for paper six which is the alternative to practical paper so the first thing that I want to say is make sure you've learned your apparatus both the names and how to draw them so let's run through some now so if I wanted to use the filtration approach for separating an insoluble solute such as sand from a solvent such as water this is what we'd use try and use a ruler where possible I am not very good at drawing as you can see so here's my beaker my funnel the filter paper what stays behind in the filter paper is known as the residue and what trains through here will be the filtrate which in the example I've given you will be water whereas the residue will be sanded if I wanted to use the crystallization method let's draw out the apparatus I'm just using these methods just to give some context to the apparatus here's your heat proof mat remember that to draw Bunsen burner it's simply an arrow pointing upwards with the word heat underneath then we'll need a tripod the little wire mesh is known as the gauze here's your evaporating basin so by applying heat here you'll drive off some of that water leaving a hydrated Crystal behind that you're allowed to cool and dry probably on the filter paper or in an oven I'm just going to quickly show you some other apparatus so here's your Bunsen Banner again your gauze this time we're just showing simple distillation which can be used to separate things like sea water from Pure Water ethanol from water now this here notice the shape of it is known as a round bottom flask we have a bung up here you may see that sometimes with a thermometer sticking into it this is an important piece of apparatus known as a condenser it helps to cool down the gas from the liquid that's evaporated so that gas down here helps to cool it down and turn it back into a liquid notice that the water goes in at the bottom of the condenser and the water goes out at the top be prepared to draw a measuring cylinder which is used to measure out volumes of liquid fairly inaccurately to improve the accuracy with which you're measuring the volume of liquid out well I'm struggling to draw this you could use a pipette or a buret which remember has a tap on it a bureau is an amazing piece of apparatus it allows you to measure volumes of liquid extremely accurately basically to the nearest drop remember you use a buret in a titration so you use that buret to add either the acid or The Alkali to a conical flask which contains an indicator and that indicator changes color when neutralization has been reached the type of indicator you pick is quite important you want to use one with a sharp endpoint so basically only has two colors she phenolphthalein methyl Orange they're both good examples don't use Universal indicator here in a titration because remember it has a range of colors which start at Red for something which is very acidic it's around pH one goes all the way through to Green which shows a neutral solution pH seven and then kind of a blue shade for very alkaline Solutions so about pH 13. so do not use usual Universal indicator in a titration a couple of other things I want to point out is if you're asked about endothermic and exothermic reactions remember in an endothermic reaction energy is taken in from the surroundings and therefore the surroundings will feel colder so if there's any bit of experiment where something's getting cold and they ask you what type of reaction is it will be endothermic an exothermic reaction is the opposite heat energy is released to the surroundings so you'll expect those surroundings to get hot if they ask you anything to do with heating alcohols you want to be very careful here with a naked Flame the reason for that is that alcohols are very flammable so if you need to heat anything safely you want to use a water bath is a good option something to consider now is rates of reaction it will vary based on what the experiment is but a good bet is to look at the amount of reactants used so that could be the mass of reactants used divided by a time frame such as 60 seconds or you could look at the amount of products formed that could be if you're looking at carbon dioxide production you can look at it from a volume of carbon dioxide produced in a certain time frame say 60 seconds use something like a gas syringe to capture that carbon dioxide but again if it's rate you need to be dividing it by time so here's a good example of this here we have calcium carbonate reacting with something like hydrochloric acid producing carbon dioxide and we're going to look at how much carbon dioxide is released in a certain time frame you might also have seen that experiment using a measuring balance and rather than looking at the volume of gas released you look at the change in mass because obviously as that gas escapes out of the top of the conical flask you'll see the mass decrease but that only works with a really heavy Mr gas-like carbon dioxide which has an mr44 something like hydrogen won't work because it only has an MR of two and then just the graphs be aware of when you should make a change what sort of graph you'll expect to see so if you were to increase the temperature involved in the rate of reaction because you've only altered the temperature you'd still expect the same massive product to be produced so be careful when you're drawing those lines it should level out at the same point the only difference is with a higher temperature you'd expect a steeper gradient and that's because the particles have more kinetic energy so they're colliding more frequently if you alter the concentration this is when you'd expect to see different quantities of product produced because higher concentration means more particles so in this case you would see the differing leveling outs with a larger surface area so for example if you were to powder the calcium carbonate solid again you'd expect to see an increased frequency of collisions so we're going to see a steeper gradient but because the mass of your reactants has remained the same again it will level out at the same point I just want to take you through a chromatography method in case they ask you to provide one it will be easy if they just give you drops of ink but if they give you something like grass and they want you to look at what pigments are found in Grass remember that your first step is to crush the sample always give apparatus with cie so we're going to use a pastel and mortar to crush and then we want to dissolve your sample in a solvent and give an example of a solvent it can be as basic as water and then you're ready to set up your chromatogram so here's a simple setup of your chromatogram we have our chromatography paper which could just be filter paper hanging off a glass rod that's held over a beaker the next thing is to make sure you have a reference line which is drawn in something like pencil because pencil is insoluble then you add your drop of pigment to that pencil line next up you need a solvent which sits at a level lower than the reference line a good solvent is water you could try ethanol and then as the solvent soaks up the filter paper the chromatography paper it will take that ink or the pigment with it and based on the number of drops you can determine how many different colors there are in the pigment if you're after finding an RF value remember you do the distance traveled by the ink drop will die divided by distance traveled by solvent they'll probably at some point ask you about safety obviously that just depends on what the experiment is but do look out for Dangerous Gases such as chlorine gas and hydrogen chloride gas not to be confused with hydrochloric acid these give off horrible fumes which are toxic and therefore these experiments are best carried out inside a fume cupboard you should always be wearing safety goggles lab coats using gloves if appropriate so do think about that another experiment they like to ask you is about the percentage mass of a particular element in a substance so what about the percentage by mass of zinc we'll use this as our example found in a sample of brass which is an alloy made up of both zinc and copper so we're interested in basically how much zinc is there in a sample of brass so in your method you want to provide a way of finding the Massive Brass so use a balance to find the Massive Brass we need to have a way of forcing one of those Metals either zinc or copper to react in order to remove its Mass from the brass the good way of doing that is by adding excess it needs to be accessed to make sure that all the metal has reacted and we're going to use sulfuric acid here now remember you need to know the reactivity series and what happens if zinc is added to sulfuric acid you make a salt zinc sulfate plus hydrogen gas effectively removing your zinc from the brass so now we point out that the substance that the mixture needs Heating and then filtering and we filter to leave behind just that unreactive copper then we wash and dry the remaining copper find the mass of copper using a balance again and to find the percentage by mass of copper in the sample you do that final mass of copper divided by the original Mass of brass Times by a hundred and then your last step is to find the mass find the percentage mass of zinc by doing 100 minus your answer from the previous step so obviously this is a very specific example where we're interested in finding the percentage by Massive zinc in a sample of brass but these sorts of questions come up an awful lot be very aware of the reactivity Series so know which of these elements will react and make sure that you're adding an excess of the acid to force that zinc to fully react and by doing that you'll just be left in this case with the copper so you can then find out the percentage by Massive copper in the sample before doing 100 minus the answer to find the percentage by mass of zinc foreign [Music]