Question

If gas bubbles are produced by a chemical reaction, how could you prove that the bubbles were composed of carbon dioxide

Answer 1

If the bubbles were composed of carbon dioxide we will confirmed by the following test:

1.    Take a small part of moist litmus paper into the tube with the carbon dioxide gas. If the CO2 gas is present, the litmus paper will turn from blue to red due to formation of H2CO3 ACID

1. With the Use of universal indicator paper. If carbon dioxide gas is present, the universal indicator paper will turn yellow.
2. By the use of lime water:

If carbon dioxide gas is present, and it run through lime water, the water turns cloudy. This is because the water is a solution of calcium hydroxid.