Chapter 2

NCERT
Class 9
Science
Solutions
3. Pragya tested the solubility of three different substances at different temperatures and collected the data as given below.

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 waters to form a saturated solution).

(a) What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 gram of water at 313K.

(b) Pragya makes a saturated solution of potassium chloride in water at 353K 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 293K. Which salt has the highest solubility at this temperature ?

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

Answer:

Solubility of Potassium nitrate at 313K is 62 gm.

i.e., 62 g Potassium nitrate is soluble in 100 g water.

Solubility of Potassium nitrate in 50 g water

(b) On leaving the saturated solution of potassium chloride (at 353k) to cool at room temperature, the solid potassium chloride will separated and form crystals. Since, decrease in temperature, decreases the solubility of solid in liquid.

(c) Solubility of the salts at 293 k are— Potassium nitrate = 32

Sodium Chloride = 36

Potassium Chloride = 35

Ammonium Chloride = 37

Thus Ammonium chloride has the maximum solubility (37) at 293 K

(d) Solubility of solid (salt) decreases with fall in temperature, while it increase with rise in temperature.

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