[0:07]Today's video is just gonna be a quick one to show you how we test for four common gases: chlorine, oxygen, hydrogen, and carbon dioxide.
[0:22]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.
[1:27]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.
[1:59]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.
[2:25]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 carbonate 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.
[3:09]So to quickly recap everything, chlorine will turn damp litmus paper white. Oxygen will relight 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.
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