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
	Solubility
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. Which 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) Mass of potassium nitrate needed to produce its saturated solution in 100 g of water at 313 K = 62 g

Mass of potassium nitrate needed to produce its saturated solution in 50 g of water at 313 
K = \(\frac{62}{100}\) x 50g = 31g 

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(b) Crystals of potassium chloride are formed. This happens as solubility of solid decreases with decreasing the temperature.

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(c) Solubility of each salt at 293 K

Potassium nitrate 32 g per 100 g water
Sodium chloride 36 g per 100 g water 
Potassium chloride 35 g per 100 g water 
Ammonium chloride 37 g per 100 g water

Note: Solubility of a solid is that amount in gram which can be dissolved in 100 g of water (solvent) to make saturated solution at a particular temperature.

Ammonium chloride has the maximum solubility (37 g per 100 g of water) at 293 K.

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(d) Solubility of a (solid) salt decreases with decrease in temperature while it increases with rise in temperature.