question_answer

  Pragya tested the solubility of three different substances at differs 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) form a saturated solution).  

Substance dissolved	Temperature (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 saturated solution of potassium nitrate in 50 grams of water at 313 K? (b) Pragya makes a saturated solution of potassium chloride in water; 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?   [NCERT]

Answer:

               (a) Solubility of potassium nitrate at 313 K (given) Mass of potassium nitrate = 62 g Mass of solvent (water) = 100 g Therefore, the mass of potassium nitrate to obtain a saturated solution at  Thus, 31 g of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 g of water at 313 K. (b) On cooling, the solubility of a salt decreases with the falling temperature Hence, the crystals of potassium chloride will separate out on cooling. (c) The solubilities of different salts at 20°C (i.e., 293 K) in 100 g of water are given in column 2 in the table. From the given data, it is clear that ammonium chloride has the highest solubility (37 g/100 g of water). (d) Generally, the solubility of a salt increases with the increasing temperature. However, from the data given in the table, it is apparent that the solubility of sodium chloride changes very little with increasing temperature.