(i) 31 g potassium nitrate is needed. (ii) Potassium chloride crystals will separate as the solution cools because its solubility decreases. (iii) Solubility generally increases with temperature, but the increase differs among salts.
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.
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(i) At 40 °C, potassium nitrate has solubility of 62 g per 100 g water. Therefore, 50 g water needs 31 g potassium nitrate. (ii) Potassium chloride will crystallise as cooling decreases its solubility. (iii) From 10 °C to 80 °C, potassium nitrate increases from 21 to 167 g, sodium chloride from 36 to 37 g, potassium chloride from 35 to 54 g and ammonium chloride from 24 to 66 g.
For more NCERT Solutions of Class 9 Science Exploration Chapter 5 Exploring Mixtures and their Separation Question Answer (2026-27)
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