What is the reason for using a lid when working with ethanol?

• A. To reduce the volume of liquid.
• B. To prevent the liquid from splashing.
• C. To ensure the apparatus remains clean.
• D. To prevent ethanol vapour from escaping because it is volatile.

Answer: (D)

Ethanol is a volatile liquid, meaning it evaporates readily at room temperature. When left open, ethanol molecules keep escaping into the air as vapour, which can be flammable and form harmful or explosive concentrations in a room. A lid helps by trapping some of that vapour inside and reducing the surface area exposed to air, so fewer molecules escape. This lowers the risk of a fire or inhalation hazards and keeps the work area safer. It’s not mainly about reducing the liquid’s volume or preventing splashes, or about keeping the apparatus clean—the key point is limiting vapour escape from a volatile liquid.