welcome to this episode from the silent revision Channel today we're looking at testing for gases for your GCSEs you need to be able to describe the test for oxygen hydrogen carbon dioxide and chlorine gas let's start off with a test for oxygen gas you can see here I've got a gas jar and I've got a burning splint well the test is if that I put a glowing splint into oxygen gas it should react might it so let's have a look at that again but a glowing splint the flames out I'm going to put it into the oxygen it should recognize so to summarise the test for oxygen is a lighter splint then blow it out and then stick it into the oxygen if the glowing splint then reignites that is the positive test to say that oxygen gas is present next is the test for hydrogen gas now in this experiment to produce hydrogen gas I'll put some magnesium and I'm gonna add some hydrochloric acid so that fizzing that you see now that is hydrogen gas being produced so the test for hydrogen gas is when you like the actual gas should make a popping sound more of a squeaky pop sound let's listen there we go okay so the test for hydrogen as we just said it's a summary with the lighter splints we place the burnings blend into the hydrogen gas and the positive test would be the hydrogen burns with a distinctive squeaky pop next we've got our test for carbon dioxide using lime water and so if we look here we can see lime water is colorless now to reduce carbon dioxide I've got some hydrochloric acid and then I'm gonna add some marble chips which is calcium chloride as the calcium chloride reacts with the hydrochloric acid we should see some fizzing which produces carbon dioxide and gas so there's my carbon dioxide gas hopefully been produced I've got my little delivery tube here and I bubble the carbon dioxide gas through the colorless lime water and if we look carefully we should see that the lime water goes from being colorless to be you know clean but cloudy we could say so precipitate that forms inside which makes it the cloudy so just to compare here we have lime water which is colorless if the bubble carbon dioxide through it forms a cloudy precipitate so to summarize we pour lime water into a test tube or beaker and we bubble the gas into the lime water and the positive test for carbon dioxide is it will turn the lime water which is colorless into an ugly cloudy color here we now have the test chlorine gas and we're going to do some electrolysis so I have some sodium chloride which is just salty water and I put it into this little piece of apparatus over here which is going to pull the chlorines to one of the electrodes so to turn on my power pack what we should see is some bubbling and that is chlorine gas being produced and normally you do this in a few cupboards so with a chlorine gas being produced what is the test to prove that it is chlorine gas well used piece of litmus paper and this example here have got some blue litmus paper which first of all we dampen and then we hold it next to the chlorine gas gradually what happens is it will go slightly red in color and then it should start to bleach in other words it should start to go white and if you look just at the end there you can see it as bleaching it or white color so we can see the bleached white section and the slight red section over there compared to normal lip miss vapor so summarize the test for chlorine gas you dampen it miss paper and you place it into the gas a positive tests if you use in blue litmus paper it should go read and then bleach in other words go whites or if you're using red litmus paper it should bleach white if you found this video useful and you think you now know how to test for those four main gases give this video a thumbs up and share it always have a great day [Music]