How Can You Test That A Gas Is Carbon Dioxide?


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Katie Harry Profile
Katie Harry answered
The most common chemical test done to prove that a gas is carbon dioxide is that it turns lime water milky. Do you have the gas given to you or do you have to first create it too?
If you have it already, then all you need is a test tube with some lime water in it (aqueous calcium hydroxide) that is sealed at the top with a delivery tube going through it and into the lime water. Now, attach the other end of the delivery tube to the carbon dioxide container/cylinder/jar. After a while, if the gas is carbon dioxide, the lime water will start to turn milky (whitish).
Now, if you have to create a gas and then test it, you need all apparatus mentioned above and some vinegar and baking soda along with a balloon and a bottle.
With the help of a funnel, put in a teaspoon of baking soda into the balloon. Do not blow it up. Now put about 2 teaspoons vinegar in the bottle and attach the balloon to it by pulling it over the bottle's top. Now leave the solution for a while (15 to 20 minutes).
As the baking soda and vinegar mix, you would see bubbles forming in the solution. You would also notice that the balloon is swelling up. Now, to check if the gas that has just been made is carbon dioxide or not, all you need to do is to take another bottle, this one filled with lime water. Detach the balloon from the first bottle by carefully holding its neck so as not to allow any gas to escape. Immediately transfer it to the lime water bottle and observe. After a while, the lime water will turn whitish.
Let's look at the two reactions that are occurring:
First, the production of carbon dioxide:
Baking soda + vinegar ------> carbon dioxide + water + sodium acetate
NaHCO3 (aq) + HC2H3O2
  (aq) ------> CO2 (g) + H2O (l) + NaC2H3O2

Now, the testing reaction:

Lime (calcium hydroxide) + Carbon dioxide ------> calcium carbonate + water
This is not this simple actually. First the carbon dioxide dissolves in water to make carbonic acid which dissociates into carbonate ions:
CO2 (g) + H2O (l) ------> H2CO3 (aq)
H2CO3 (aq) + 2OH- (aq) ------> CO32- (aq) + 4H2O (l)

Then this carbonate reacts with calcium (dissolved as calcium hydroxide), to produce calcium carbonate which is insoluble (this explains the milky appearance of the solution as precipitate of the carbonate is formed). Let's take a look at this:
Ca2+ (aq) +CO32- (aq) ------> CaCO3 (s)

If even more carbon dioxide is bubbled into the solution, the color would disappear once again as the carbonate is converted into the very soluble bicarbonate.

Anonymous Profile
Anonymous answered
You can try putting a burning splint in the test tube with the gas and it will go out. This is just a a lack of O2.
Anonymous Profile
Anonymous answered
If you have carbon dioxide it will turn limewater cloudy.
Anonymous Profile
Anonymous answered
The solution turns like I think a little milky anyway you should totally watch the video instead of reading y'all understand better
Anonymous Profile
Anonymous answered
Get a glass and fill it with limewater then use a straw and blow into it. It shows that there is carbon dioxide in your breath as you breathe out. The limewater will turn cloudy after a couple of minutes.

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