Question

What is the effect of the addition of sugar on the boiling and freezing points of water?
A. Both boiling point and freezing point increases
B. Both boiling point and freezing point decreases
C. Boiling point increases and freezing point decreases
D. Boiling point decreases and freezing point increases

Answer 1

Hint: At atmospheric pressure, the freezing point of a liquid is the temperature at which it transforms from liquid to solid. The boiling point of a liquid is defined as the temperature at which the vapour pressure of the liquid becomes equal to the atmospheric pressure of the liquid’s environment. At this temperature, the liquid is converted into a vapour.

Complete answer:
A mixture of sugar and water is a non ideal solution with negative deviation as interaction between solute and solvent is more than the individual component. A solution that does not obey Raoult's law for all the concentration and temperature ranges it is known as a non-ideal solution
Sugar is a non-volatile solute. Adding sugar to water will raise the boiling point and decrease the freezing point of water.
The boiling point of liquid is influenced by the pressure. If the external pressure is less than one atmosphere, the boiling point of the liquid is lower than the standard boiling point. When the external pressure is more than one atmosphere, the boiling point of liquid rises. The boiling point will be the same if the pressure is equal to one atmosphere.
Hence, the correct option is C. Boiling point increases and freezing point decreases.

Note:
The type of molecules that constitute a liquid affect the freezing point. The freezing point rises when the intermolecular interactions between these molecules are high. On the other hand, if the intermolecular forces of attraction are weak, then the freezing point becomes low.