You are here
Answer the following questions with the help of the data given in Table 5.4.
(i) What mass of potassium nitrate would be needed to prepare its saturated solution in 50 g of water at 40 °C?
(ii) A student makes a saturated solution of potassium chloride in water at 80 °C and leaves the solution to cool at room temperature (25 °C). What would she observe as the solution cools? Explain.
(iii) What is the effect of a change in temperature on the solubility of salts? Also, compare the changes in the solubility of the four given salts with increasing temperature from 10 °C to 80 °C.
(i) What mass of potassium nitrate would be needed to prepare its saturated solution in 50 g of water at 40 °C?
(ii) A student makes a saturated solution of potassium chloride in water at 80 °C and leaves the solution to cool at room temperature (25 °C). What would she observe as the solution cools? Explain.
(iii) What is the effect of a change in temperature on the solubility of salts? Also, compare the changes in the solubility of the four given salts with increasing temperature from 10 °C to 80 °C.
View Answer
(i) At 40 °C, potassium nitrate's solubility is 62 g per 100 g water. For 50 g of water, mass needed = 62 ÷ 2 = 31 g .
(ii) As the potassium chloride solution cools from 80 °C to 25 °C, solubility falls, so the excess salt crystallises out and is seen as solid crystals.
(iii) Solubility generally increases with temperature. The rise is steepest for potassium nitrate (21 → 167), moderate for ammonium chloride and potassium chloride, and very small for sodium chloride (about 36 → 37), which barely changes.
| Part | Data used | Answer |
|---|---|---|
| (i) Potassium nitrate in 50 g of water at 40 °C | 62 g per 100 g of water at 40 °C | half the water → 62 ÷ 2 = 31 g |
| (ii) Saturated potassium chloride, 80 °C → 25 °C | 54 g at 80 °C, falling to about 35 g near 25 °C | solubility drops, so the excess salt crystallises out as solid |
| (iii) Effect of temperature | 10 °C → 80 °C for all four salts | solubility generally increases : potassium nitrate rises steeply (21→167), ammonium chloride (24→66) and potassium chloride (35→54) rise moderately, sodium chloride hardly changes (36→37) |
