Question

Take some water in a beaker and place a thermometer in it. Heat the beaker on a spirit lamp. Note the boiling point of water. Repeat the activity, adding salt or sugar to the water and note the boiling point again. What do you infer from it?

Answer 1

• The boiling point of pure water is 100°C at normal atmospheric pressure. When we add salt or sugar to water and heat it, the water boils at a temperature slightly higher than 100°C. This happens because the dissolved salt or sugar makes it more difficult for water molecules to escape as vapour.
• From this activity, we learn that the boiling point of a liquid can change when another substance is dissolved in it. Adding salt or sugar to water raises its boiling point. Thus, the presence of dissolved substances affects the physical properties of a liquid.