Question
Explain the following:
(i) The boiling point of water (373 K) is abnormally high when compared to that of H2S (211·2K).
(ii) Liquids like ether and acetone are kept in cool places.
(iii) Tea or coffee is sipped from a saucer when it is quite hot.
Solution
(i) The hydrogen bonding in water molecules increases the intermolecular forces of attraction in water. Due to this, greater energy is needed to separate the water molecule so as to convert it into water vapours and hence boiling point of water is relatively higher.
(ii) Liquids like ether and acetone are quite volatile. Since the rate of evaporation decreaes with the decrease in temperature, so these liquids are kept in a cool place so as to avoid their evaporation.
(iii) It is because evaporation causes cooling and the rate of evaporation increases with the increase in surface area. Saucer has a large surface area, therefore, tea or coffee in it cools quickly. Hence, tea or coffee is sipped from the saucer when it is quite hot.
(ii) Liquids like ether and acetone are quite volatile. Since the rate of evaporation decreaes with the decrease in temperature, so these liquids are kept in a cool place so as to avoid their evaporation.
(iii) It is because evaporation causes cooling and the rate of evaporation increases with the increase in surface area. Saucer has a large surface area, therefore, tea or coffee in it cools quickly. Hence, tea or coffee is sipped from the saucer when it is quite hot.
