Pragya tested the solubility of three different substances at different temperatures and collected the data as given bel

Solution

(a)        As per table : 100 g of water dissolves potassium nitrate = 62 g

            ∴          50 g of water dissolves potassium nitrate =  = 31 g.

                  Hence, 31 g of potassium nitrate would be needed to produce a saturated solution of potassium nitrate.

                  (b)        On changing the temperature of the saturated solution from 353 K to room temperature, cooling takes place. Since the solution is saturated, solubility of potassium chloride will decrease due to cooling. Consequently, the crystals of potassium chloride will be observed in the solution. As the solubility of potassium chloride at 353 K is 54 g while at 293 K (Room temperature) it is 35 g, therefore 54 − 35 = 19 g salt will precipitate out.

                  (c)        The solubility of a solute is the maximum amount of solute that can be dissolved in 100 g of the given solvent to obtain a saturated solution at a particular temperature. Hence, the solubilities of different salts at 293 K are :

                        Salt                                          Solubility at 293 K

            (i)         Potassium nitrate                                  : 32 g per 100 g of water.

            (ii)        Sodium chloride                                  : 36 g per 100 g of water.

            (iii)       Potassium chloride                               : 35 g per 100 g of water.

            (iv)       Ammonium chloride                : 37 g per 100 g of water.

                        Thus, ammonium chloride has the highest solubility at this temperature of 293K.

            (d)        The solubility of a salt increases with an increase in temperature. The solubility of a salt decreases with a decrease in temperature.