Question

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).

Substance dissolved	Temperature in K
	283	293	313	333	353
Potassium nitrate	21	32	62	106	167
Sodium chloride	36	36	36	37	37
Potassium chloride	35	35	40	46	54
Ammonium chloride	24	37	41	55	66

(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? Explain.

(c) Find the solubility of each salt at 293 K. What salt has the highest solubility at this temperature?

(d) What is the effect of change of temperature on the solubility of a salt?

Answer 1

(a) At 313 K, 62 grams of Potassium nitrate dissolved in 100 grams of water. So to produce a saturated solution of potassium nitrate in 50 grams of water, we need
62 x 50 = 31 grams of potassium nitrate
100

(b) Some soluble potassium chloride will separate out in the form of crystals at room temperature because the solubility of potassium chloride will decrease with decrease in temperature.

(c)
(i) Solubility of Potassium nitrate at 293 K is 32 grams.
(ii) Solubility of Sodium chloride at 293 K is 36 grams.
(iii) Solubility of Potassium chloride at 293 K is 35 grams.
(iv) Solubility of Ammonium chloride at 293 K is 37 grams.
The solubility of Ammonium chloride is highest at this temperature.

(d) The solubility of salt increases with increase in temperature.