Pick the best test for identifying each of the gases carbon dioxide, hydrogen, and ammonia. Choose from these test options:

lime water


melting point

glowing splint

flaming splint

water solubility

Expert Answers

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The best choice to identify carbon dioxide gas is the limewater test. Limewater is an aqueous solution of calcium hydroxide. When CO2 is bubbled through lime water a precipitate of calcium carbonate forms turning the solution cloudy and white.

Here’s the equation for the reaction:

`Ca(OH)_2(aq) + CO_2(g) -gt CaCO_3(s) + H_2O_((l))`

Hydrogen gas can be identified using a flaming splint. Hydrogen is collected in a test tube. A burning wood splint is held near the top of the test tube as the stopper is removed. If the gas in the tube is hydrogen, which is flammable, it will ignite with a popping sound.

Ammonia gas is very soluble in water. When bubbled through a hose and into a flask of water, it dissolves produces an aqueous solution of ammonium hydroxide. Bubbles of hydrogen gas and carbon dioxide will both rise to the surface as gas bubbles. The presence of dissolved ammonia can be verified by checking the pH of the solution.  Ammonium hydroxide is basic so it has a pH above 7 and will turn red litmus paper blue.

The reason for ammonia’s solubility compared to other the other gases is that it’s very polar and it forms hydrogen bonds with water molecules.

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