today's video is just going to be a quick one to show you how we test for four carbon gases chlorine oxygen hydrogen and carbon dioxide let's start with the test for chlorine first of all you're going to need a test tube full of your sample gas which you think might contain chlorine next you need to take a piece of blue litmus paper and dampen it then as you put the damp blue litmus paper into the test tube if chlorine is present the paper will turn from blue to white something to be aware of though is that you might sometimes find that the paper briefly turns red before turning white this is because the chlorine dissolves in the water on the damp paper and forms hydrochloric acid which because it's acidic will turn the blue litmus paper red however the paper will then quickly go white as it gets bleached by the chlorine also remember that chlorine is poisonous so if you were to do this experiment you'd want to wear a mask or do it in a fume cupboard next up we have the test for oxygen for this test we need a glowing splint so one without a flame but which is still glowing red at the end we then get our sample of gas and place the splint into the tube if the gas is oxygen the glowing splint will relight because burning requires oxygen and so if we supply loads of oxygen to our splint the reaction will spark up again the test for hydrogen also involves a test tube and a splint this time though the test tube of course contains hydrogen and the splint is burning when we move them close enough together we'll suddenly hear a squeaky pop as the heat energy provided by the flame causes the hydrogen to burn with the oxygen in the air to form water the last test for carbon dioxide is a bit different this time we have to get our gas sample in one tube and an aqueous solution of calcium hydroxide otherwise known as lime water in another we then bubble the gas sample through the calcium hydroxide and as long as the gas is carbon dioxide this will cause this solution to go cloudy as the co2 and calcium hydroxide react to form calcium carbonates and water the reason it goes cloudy is because calcium carbonate is a solid and it's all these little solid particles that make it appear cloudy so to quickly recap everything chlorine will turn down polymers paper white oxygen will re-light a glowing splint hydrogen will give us a squeaky pop when exposed to a lit splint and carbon dioxide will cause lime water to go cloudy anyway that's all for today so hope you enjoyed it and we'll see you next time