When determining the boiling point of a liquid, why is the bulb of the thermometer kept in the vapour over the liquid instead of being immersed in the liquid?
Answer: In determining the boiling point of a liquid, the thermometer should be kept in the vapour over the liquid instead of being immersed in the liquid. The boiling point of the pure liquid is equal to the temperature of its vapour. The addition of impurities to the liquid increases the boiling point of the liquid. Therefore, while determining the boiling point of a liquid, the bulb of the thermometer is placed in contact with the vapour above it instead of being immersed in the liquid.