hi folks some people have been away for our investigation uh regarding the pop test and lime water test and using those tests to determine the identity of four unknown chemicals what I've decided to do is record myself performing those experiments so that those people who have been away have a set of results that they can use in order to still do the write up of the report in order that they can still earn the marks for this assessment my video editing editing skills aren't that great so what I'm going to do is pause recording so I can set things up and then resume recording when I'm ready to record again um I haven't worked out how to go back and edit videos after I've made them so this video won't necessarily uh be the most polished video you'll see but bear with me it should give you the information that you need okay so folks I've got some samples here and you I've got my equipment mostly set up you might notice I've got a few more pieces than you had for example I've got a few more test tubes and whatnot uh but that's just to make the record a bit quicker I've also got some distilled water here the water's been temporarily disconnected while I'm filming so normally I'd rinse with tap water but a little bit of distilled water won't affect the outcome of the result okay so the first thing we need to do with our s which are behind my waste Bucket over here is we need to do the pop test okay so if our chemicals give a positive result for the pop test that means that they've produced hydrogen gas and if they produced hydrogen gas when reacting with an acid that means that the substance is likely to be a metal so what's important is that when we do the pop test we're looking to see is it bubbling firstly uh because if it's not producing a gas we know that we're going to have either a metal a carbonate or a salt if it's not producing a gas at all that means that it's likely to be a salt that we've mixed with our acid um and so we don't need to do the pop test or the lime water test in that case however if it is bubbling we need to determine secondly what is that gas is it hydrogen gas or is it carbon dioxide gas or is it some unknown gas okay so the test for hydrogen gas is the pop test and it uses the least amount of chemical that's why we tend to do it first so I've got a sample set here uh let's call it sample set X okay so I'm going to take out X1 okay my first unknown sample and uh oh this one I might need to actually see what I'm wearing gloves I'll tip it into my my gloved hand okay okay now the idea is we don't want to use all of our chemical sample all right because if we need to do the lime water test after we've done the pop test then we need to have some of our chemical in reserve but if I just show you there what that looks like so that's our first chemical now we can see that that does look like strips of a metallic substance and quite likely that's what it is but we want to confirm that by doing the pop test so I've got a test tube here and I'm going to put these unknown strips of substance in there uh I might be able to possibly do a little bit more and still have some spare okay and so let's put substance one our first unknown off to the side all right and I'm going to need to have some matches ready to go and I'm going to need to have some acid as well okay so I've got some acid here and what I'm going to do is I'm going to have to do this a bit carefully and quickly I'm going to pour some acid on top of my unknown there doesn't have to be a precise measurement okay it doesn't have to be exactly sort of 10 m 20 Ms anything like that we just want to see see whether or not it reacts first of all now I might not always be able to hold it up to the laptop but you can see there that that one is definitely bubbling away okay so that's definitely producing a gas all right so we need to check this in terms of will it pass the pop test or the lime water tests okay now the tricky bit is trying to find a way to strike a match while I'm still holding the gas there here we go multitasking for the win all right and before the match burns out let's take that and put the match underneath oh that was nice okay so substance number one gave a successful pop test that means that it gave us a pop it gave us a positive result which is nice but that also means that the gas that's being produced it's still reacting away there that gas that's being produced is hydrogen gas okay uh and that's that's what the pop test tells us that pop sound which is described as a squeaky pop tells us that that gas was hydrogen gas now I gave out a sheet for people to write their results on today but I'm going to write my results on the board and I'll uh show the sheet results later but for now I've got the board behind me it's a bit easier so for substance number one in set X I'm going to say it gave a positive pop test and therefore substance number one is most likely to be a metal now because I've worked out that substance number one is most likely to be a metal I don't need to do the lime water test for substance number one okay so you know if I if I if I didn't get a positive pop test I would have had to have done the lime water test with substance number one as well but because I've got a positive result I know that that gas is hydrogen I know that acid plus metal gives hydrogen and a salt so I know what this unknown substance is so I don't need to keep testing it because I already know what it is okay so that's substance number one let's move that around okay substance number two we're going to have to do some more examples here and I might just need to get something to fish that out with let's have a look so we're going to do the pop test for all four of them first and then we're going to worry about oh momentary unexpected pause there uh I just briefly interrupted but that's okay that's what happens sometimes all right so we were at sample number two okay so I've got my second sample here now my second sample here is a bit of a a white powder there okay um sort of looks a bit like flower I suppose okay and again I don't want to use all of this stuff up but I do want to use enough to get well if it's going to generate a Gess if it's going to react at all I want to be able to use enough to get a decent reaction out of it okay right so let's put that down there all right and now same procedure again I'm going to pour some acid in there and whoa that's definitely bubbling away don't know if you could hear that or you can see that that's bubbling away okay so that's definitely creating a gas now the question is is it creating hydrogen gas or carbon dioxide gas or is it creating some third sort of unknown gas okay so I'm going to strike that match it seems to be reacting fairly quickly there actually okay and let's stick the match inside there and no pop in fact the match went out okay so that would indicate to me that the gas that we had was not hydrogen gas so that substance there was not a metal and that's not really that surprising it didn't really look like a metal most metals don't present as white powders okay so it's probably some sort of salt or it might have been a carbonate okay so I'm going to turn to my results on the board I know you can't see them but I can and again I'll go through the results at the end and I'm going to say uh for substance number two no pop and so that means that for substance number two I am going to have to do the lime water test in order to see whether or not I can get a pop with that okay all right yeah that one stop reacting rather quickly all right so now I've got a fresh test tube we can move on to substance number three substance number three there is another white powder okay um a lot of salts and carbonates do look very similar it has to be said it doesn't mean they are exactly the same substance though okay so just because things look the same in chemistry does not mean they are the same in fact you can see on the screen there I've got some chemicals over here this bottle here has distilled water this one has lime water or calcium hydroxide believe me they are not the same uh neither of them are safe to drink but for very very different reasons okay this one I said it looks like flour it actually has a texture that looks a bit more like icing sugar now that I sort of examin it a bit more closely put a bit in there and see how this one reacts in a moment okay always putting the lid back on the chemicals uh when I'm not using them it's the same for the acid there as well uh you just don't want to risk contaminating your chemical but also it's much less likely that you going to spill anything if you put the lids on once you've finished using them all right so same deal again me get that one out of the way for a second so once more in with the acid again I'll put that lid on properly in a minute put the test tube over and that one is also bubbling away like mad there okay so that's definitely generating a gas of some sort okay so I'll just hold the test tube over there for a second notice I'm holding the test tube up quite high above smaller test tubes this top test tube I'm not putting it all the way down it's not completely covering the lower test tube I'm actually leaving a lot of room up here for the gas to collect that's important if we want to have a successful pop test or at least if we want to give it the best chance of being successful if you have it right the way down there's only a small room for the gas to collect and even if it is hydrogen gas you're unlikely to detect it uh with a lit match okay I'm not being careless when I'm dropping the matches there I just I've only got two hands and I need both of them all right let's stick the match in there and all right there was no pop there the match went out so that was generating a gas substance number three but once again no pop so I'm going to turn to my results on the board and I'm going to write substance number three no pop so for substances two and three I need to do the lime water tests because they both bubbled away but it wasn't hydrogen gas so I need to check to see if that gas is carbon dioxide but before I do that I have one more pop test that I need to do and that is for substance number four now substance number four you'll notice looks a bit different from some of the other substances that we've got okay substance number four there is a nice blue solid powder okay and uh actually I do know what these substances are I should say these substances when we give you unknown substances quote unquote um they're only unknown to you we we teachers do know what they are we wouldn't give you substances that we didn't know what they were that would be incredibly irresponsible I do know what this substance is and I actually do know how it's going to react but the point of this investigation is what do you do when you don't know what the chemical is what do you do and how do you determine what the chemical is okay all right so putting the lid back on that [Music] one and matches out the way there for a second and once again going to pour a bit of acid onto that and just see what happens and nothing much really seems to be happening there at all I pulled the acid on there and that's not bubbling away at all that's not doing anything that's just sitting there at the bottom of the test tube really not doing very much of anything at all okay so you can see that that is actually a powder it's not really even dissolved at this point uh the reason the top looks a bit blue is it's just reflecting off of uh what's on the bottom there so that didn't even bubble now the fact that it didn't even bubble tells me that no gas was produced now if no gas was produced it's not worth holding the test tube over it to try and collect the gas uh in order to do the pop test and it's also not worth doing the lime water test either because both tests operate on the idea that a gas is going to be produced if no gas has been produced then you can't do either test so for number four I'm not just going to write no pop I'm going to write no gas so it didn't produce hydrogen gas it so it can't be a metal it didn't produce carbon dioxide gas because it didn't produce any gas at all therefore it can't be a carbonate that we've mixed with our acid the only other option based on what I've told you is that it has to be a salt if it's neither a metal or a carbonate it must be a salt so for number four because there was no gas produced I can say this has to be a neutral salt and so I already know what number four is I don't need to test it further so that's good I've done the pop test the first one gave us a positive pop test so that one was a metal we know what that is we don't need to test that any further the second and third one counting my fingers on the screen there second and third they both produced a gas but it wasn't hydrogen gas so we need to test those further with the lime water test the fourth one didn't produce any gas at all so it can't give us a positive pop test or a positive lime water test because there's no gas being produced so it must be a neutral salt because we've only got three options for our unknowns okay metal carbonate neutral salt if it can't be a metal and it can't be a carbonate it must be a neutral salt so I know what substance one is and substance 4 is straight away so now I need to do my lime water test only with the two that I'm not sure of yet which is substance 2 and substance 3 I'm going to pause the video for a minute so I can set that up and then we'll resume with the lime water test for substances two and three all right folks and we're back okay so we have samples two and three that we need to do uh so this one up the front here is sample number three this one up the back here is sample number two um maybe I could swap those around actually that might be the way to go okay so sample number two now up the front sample number uh three now at the back so these are the two samples that we need to do the lime water test for now what I've got is another two test tubes next to them here okay where the lime water is actually going to go into all right so I'll show you the ones in the back so I've got two test tubes here okay so this one has the sample in it this one's going to have the lime water in it and what I'm going to have between the two of them is this thing here it's called a gas delivery tube okay it delivers gas from one test tube into the other test tube into the lime water okay so I'm going to do sample number two up the front here first uh I need to pour I poured my solid in here I haven't poured the acid in there yet I need to pour my lime water into this one first I need quite a bit of lime water it needs to be sort of about half full maybe slightly over half full okay now I've got a big container of lime water here hopefully I can pour it without spilling it let's do it over the waist bucket here there are other ways you can pour it to make sure you don't spill but who has time for that okay I'll do that one there and I'll just put the lid back on I'll pour the second one in a minute okay just so it's not exposed to the atmosphere if there's any sensitivity to carbon dioxide exposure which there can be with lime water this second one isn't waiting uh being exposed to the atmosphere while we're doing the first test okay so once again I've got my acid so the acid is going to go into the test tube that has my solid in it and again I'm going to add oh it's bubbling over nicely there I don't know if you can see that bubbling all the way up let put that in there quickly and plug my gas delivery tube into my lime water there and I don't know if you can see that but that's bubbling away quite nicely there the lime water's clear but that is already starting to change to a sort of milky white color I think okay oh hello was the best angle there the best angle there wow that was bubbling Away really quite quickly at first and then it's slowed down a bit but that is definitely I'm sure you can see it on the camera there it's definitely got a sort of milky white kind of color that lime water that was a very quick change I have to say um so that is confirmation that the gas that was developed uh in that reaction with chemical number two and it's still coming out although a bit slower uh that carbon dioxide gas and that means that the substance that's been reacting with our acid must be a carbonate so I can go up to my table for example number two lime water test uh it turned the lime water milky therefore it is a carbonate okay now that milky color change won't last um the too long it'll last for a few minutes and then it will change back oh I can see where it bubbled over here let's just clean up after ourselves cleaning as you go is a nice way to make sure we don't have a big huge mess to clean up at the end okay all right so that was good that was that was quite exciting actually the lime water test is one of those ones that can be a little bit um finicky sometimes it doesn't always want to go depends bit on how fresh the lime water is and also how much gas it's produced okay all right so but quite happy with that one so let's take actually maybe what I can do is I can get another gas delivery tube that might be the way to go I'll leave that one there yes we come we come well prepared okay we've got more than one guest delivery tube so I'll just I'll leave that first one set up uh but I might actually move it here we are so I can just go off to the side there it's not hurting anyone and we can have a look at our second one here okay so this is sample number three I've had to use quite a bit of powder for this one okay this is the last one we need to test uh now I need to put my lime water in before I do anything else so again I'm not putting this in with the powder I'm putting this in the the second test tube so the the gas is transferred from the test tube with the powder to another test tube with the lime water [Music] okay probably put that one back on the trolley now I don't think I'm going to need that one get these ones too actually I don't think I'm going to need those okay and now I need to be very quick once again I'm going to pull my acid in and very quickly that on that in there it's definitely it's definitely bubbling it's not bubbling quite as quickly is it going to produce enough bubbles to transfer across or is it just going to Fizz out that's the real question C on give us a few bubbles I mean the last one was so quick you sort of expect that this one might end up going a bit better uh but no it doesn't seem to want to produce as many bubbles and it seems to be slowing down a bit and it's fizzing okay so that leaves us with a bit of a quandry then for that last one because the the line water was the same so we know the lime water is fine but no actual bubbles came out of the gas delivery tube now what that tells me is that the gas that's being produced in here uh there's probably not enough of it or it's not being produced quickly enough to cause bubbles to appear in the lime water and when that happens there's not a heck of a lot we can do about that and so the best and most accurate thing we can say at this point is to say that the result for this experiment is inconclusive okay CU that one's that one's basically finished reacting it's not really bubbling away anymore but it didn't produce enough gas to get even one bubble to go through that lime water now sometimes this happens if it doesn't produce enough gas you'll get an inconclusive result so you can't necessarily tell what the substance is not because the test was a bad test but because the amount of gas that produced wasn't enough for us to actually do the test okay and so that sometimes happens particularly when you've got powders they because they're crushed up they tend to react very quickly they release all of their gas at once instead of releasing it slowly okay The Last One released a lot of gas at once but it sort of kept reacting kept releasing gas uh for a few minutes which was quite nice uh but this one seemed to have released all its gas it's once and it it hasn't kept producing it so it hasn't had a nice steady stream of gas being produced to produce a stream of bubbles which is what we need for the lime water test so strictly speaking we should probably say that that test is inconclusive but when we go to analyze our results we can actually say why it was inconclusive we can say not enough bubbles were produced but we can also say what we think was the case based on the results okay we can be reasonably sure that it's not uh a metal because it did produce enough gas for a pop test you don't need a lot of gas for the pop test and it didn't pass that so it can't be a metal um which means that the gas It produced is either carbon dioxide or something else now what the something else is well we need another test for that and we don't have it now as it happens I do know what this substance is because again I was the one who put this experiment together and so I know that that substance is actually a carbonate but it it didn't produce enough gas uh to actually make the lime water change successfully okay but that gives you something to talk about if you don't know that it's a carbonate you can say Well it bubbled I know that the only three options are going to be metal carbonate or neutral salt neutral salts don't generally produce gases when they react with acids so if it produced a gas and it's not hydrogen chances are it's carbon dioxide which means chances are pretty good this is a carbonate so and you're allowed to do that you're allowed to use sort of logic that's based on the results you got even if the results weren't perfect to draw conclusions but you have to be clear when you're drawing those conclusions that actually your results weren't conclusive this is what you are inferring from the results it's an educated guess it's not certain okay all right so I'm going to pause the video again so we can talk about the results after I've cleaned all this up okay folks so I've just changed the view of this recording so you should be able to see what's on my screen and I should just appear in the corner of the screen you don't particularly need to see me for this bit but just so we can have a look at the results together um I think you can see my mouse on the screen as I move it but if not uh that's fine I'll be talking about the results here so I do have the results on the board behind me but the pen is a bit faint and doesn't show up that well on camera so I've written down the results uh which should be appearing on your screen now so these are the experimental results I've written down the group members obviously me and the sample set used was Sample set X okay all right so for our first known in Sample set X the choices are it's either a metal a carbonate or a neutral salt it gave us a positive pop test so it went pop uh when we collected the gas and lit the match therefore it was hydrogen gas that we produced we know that an acid plus a metal gives us a salt plus hydrogen gas so given that we already know we had an acid in there the unknown must have been a metal which means sample one must have been a metal so I can reason that out and I can conclude here uh where it says type of substance next to number one I can say this substance was a metal scrolling down a bit for sample number two sample number two we tried the pop test it didn't give us a pop but it did produce a gas and when we ran that gas through lime water in the lime water test it turned the lime water milky in fact it turned it milky remarkably quickly so the gas that was produced the gas that turns lime water milk is carbon dioxide gas and we know that an acid plus a carbonate produces a salt plus water plus carbon dioxide gas so the unknown in that situation must have been a carbonate so sample two from set X of our chemicals uh must have been a carbonate going on to number three this was our one that we couldn't quite be sure of it didn't give us a pop in the pop test okay we did have enough gas produced uh for a pop test but it didn't go pop so we know it wasn't hydrogen gas so we know it's not a metal but it didn't produce enough gas for a successful lime water test so technically the results of this test are inconclusive however if we scroll up again we know that the options we have are it's either a metal a carbonate or a neutral salt it's one of those three things since it didn't go pop we can rule out metal so it's either a carbonate or a salt a neutral salt and generally speaking salts when they react with acids if well generally they don't react with acids so generally they're not going to produce a gas at all in this case I I know that it shouldn't have reacted uh sorry I know that any neutral salt shouldn't have reacted in this experiment uh to produce a gas so the fact that it did produce a gas tells me that this is likely a carbonate but the reality is if I didn't know in advance whether whether or not this was a carbonate I would have to say this result is inconclusive um but I suspect that it's a carbonate you're allowed to say that you know the results are inconclusive but this is what I think you just have to qualify that in your discussion and say you know I could be wrong but this is what I think and this is why I think that so for number three here you could say I think it's a carbonate because it it produced a gas that wasn't hydrogen and I don't expect neutral salts to produce a gas that's fine you could also say it failed the lime water test so I I would conclude that it's a neutral salt you can make that conclusion if you like okay probably the safest and most reasonable conclusion would be to say the results are inconclusive because we weren't able to get enough gas to successfully complete the lime water test so we can't tell whether or not it's a carbonate or a salt we we can rule out metal okay and that might be something that you want to add in there in fact I can probably add that in here myself I can probably say not metal okay oops let's make that a capital M for metal there so not metal we know that but is it a carbonate or a salt you sort of have to provide reasons for what you think it might be but you can't say for sure and you have to be honest about that and that's really the most important thing in science reports be honest about your results don't don't write what you think the person reading your report wants to hear write what you can say truthfully based on the results you're allowed to have an educated guess and you're allowed to defend an educated guess with evidence from your experiment and with reasons that you might have uh based on what you've learned or what you've researched but don't make things up uh in order to try and impress your te teaches okay um that's that's not impressive in science that's not how science works okay making things up is not what we want to do for the fourth one the final part of our uh unknown sample uh no gas was produced at all so it wouldn't give a successful pop test or a successful lime water test it wouldn't go pop it wouldn't turn lime water milky because it didn't produce a gas so it can't be a metal it can't be a carbonate it must be a neutral salt just by process of elimination okay so number four there is a neutral salt okay folks well I hope that was somewhat enjoyable uh and hopefully not too long and for those of you who didn't get to do this yourself you can use this set of results to still write up a report so that you get an idea of the sorts of things that need to be written up in a science report which is very important not just this year but going forward into future years all right folks I think I'll sign off let's see if I can minimize this and stop the recording by for now