What is the purpose of adding ice or cold water when collecting gas in this context?

• A. To warm the gas
• B. To speed up the gas collection
• C. To cool down the gas so it condenses into a liquid
• D. To increase the solubility of the gas

Answer: (C)

Cooling the gas during collection helps remove water vapour from the gas mixture. When gas is produced and collected over water, it carries water vapour with it. If the gas is warm, this water vapour stays in the gas and adds to its volume. By adding ice or cold water, you lower the temperature, causing the water vapour to condense into liquid water and stay in the bath rather than in the collected gas. This gives a drier gas and a more accurate measurement of the actual gas volume.