Addition of soluble impurities into a liquid and solid respectively causes:

Explanation

Whenever a soluble, non-volatile impurity is added to a liquid, some of the solute particles tend to migrate toward the surface of the liquid, and some will remain in the bulk liquid. Due to this, an obstruction is caused by the volatile nature of the liquid. In other words, it becomes harder for the liquid molecules to vaporize due to the obstruction caused by the molecules of the added impurity. The result is that the net vapor pressure of the mixture becomes lower than that of the pure liquid, as fewer liquid molecules can go into the vapor phase. We know that the boiling point of a substance is the temperature at which the vapor pressure of the substance equals the external pressure. What happens during boiling is that we raise the temperature of the liquid, thereby raising its vapor pressure, until it becomes equal to the atmospheric pressure and starts to boil. So, when the impurity is added, vapor pressure is reduced, and thus, more heat needs to be supplied to raise it to the external pressure and make the mixture boil. Hence, the presence of soluble impurities increases the boiling point of liquids. The higher the concentration of impurity, the higher will be the elevation in boiling point. When we add impurities to the pure substance, the melting point of the solid is decreased because impurities weaken the lattice structure of solids due to which it becomes less stable and melts before its original melting point. This is called melting point depression.