Q. 273.7( 23 Votes )

# Pragya tested the solubility of four 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? 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 in temperature on the solubility of a salt?

Answer :

(a) Mass of KNO3 to produce a saturated solution of KNO3 in 100 gm of water at 313 K = 62 g

Therefore, mass of KNO3 in 50 g of water at 313 K = 62.050/100 = 31.0 g

31 g of potassium nitrate is needed to produce a saturated solution of potassium nitrate at 313 K.

(b) When the saturated solution of potassium nitrate is left to cool at room temperature, then solid potassium chloride will separate gradually from the solution. Solubility of a substance depends on the temperature. Solubility increases with increase in temperature of the solution. Room temperature is lower than 313 K hence, the crystals of solute will separate out from the solution.

(c) The solubility of different salts at 293 K is: Potassium nitrate 32g ; Sodium chloride 36g; Potassium chloride 35g; and Ammonium chloride 37g. Ammonium chloride has the highest solubility of 37 g at 293 K.

(d) Solubility of a substance depends on the temperature. The given data shows that the solubility of a salt increases on increasing the temperature.

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