What is the purpose of ice or cold water in a gas collection setup?

• A. To warm the gas so it stays in a gaseous state.
• B. To cool down the gas so that it condenses and turns into a liquid.
• C. To neutralize any acidic fumes.
• D. To increase the gas pressure.

Answer: (B)

Cooling the gas lowers its temperature, which makes condensation possible. When gas produced in a reaction passes through an ice bath or cold water, its molecules lose kinetic energy. If the gas contains water vapour, or if the gas itself can be liquefied at that low temperature, the vapour condenses into a liquid on the cold surfaces and can be collected as a liquid. This is the intended use of the ice or cold water in the setup. Heating would keep the gas gaseous, neutralising fumes isn’t achieved by cold temperatures, and simply cooling doesn’t inherently increase pressure in this context.