Pragya tested the solubility of three different substances at different temperatures and collected the data as given below (results are given in the following table, as grams of substance dissolved in 100 grams of water to form a saturated solution).

(a) What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 grams of water at 313 K ?
(b) Pragya makes a saturated solution of potassium chloride in water at 353 K and leaves the solution to cool at room temperature. What would she observe as the solution cools ? Explian.
(c ) Find the solubility of each salt at 293 K . Which salt has the highest solubility at this temperature ?
(d) What is the effect of change of temperature on the solubility of a salt ?

Explanation

(a) At 313 K, in the saturated solution
Amount of potassium nitrate dissolved in 100 grams of water = 62 g
Amount of potassium nitrate dissolved in 50 grams of water = (62 g) `xx ((50 g))/((100 g)) = 31 g`
(b) When the saturated solution prepared at 353 K is cooled to room temperature (about 298 K) the solubility of potassium chloride in water will decrease. It will slowly start separating as a crystalline white residue at the bottom of the container.
(c ) The solubility of the salt in a water is defined as :
the maximum amount of the salt which is dissolved in 100 g of water (or any other solvent) to form a saturated solution at a given temperature
In the light of this, at 293 K
Solubility of potassium nitrate = 32 g per 100 g of water
Solubility of sodium chloride = 36 g per 100 g of water
Solubility of potassium chloride = 35 g per 100 g of water
Solubility of ammonium chloride = 37 g per 100 g of water
Ammonium chloride has the maximum solubility (37 g per 100 g of water) at 293 K
(d) With rise in temperature, the solubility of all the salts in water increases. This has been shown by the data given in the table. Similarly, when the temperature is decreased, the solubility of these salts in water decreases.