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JAMB Chemistry 1982 Question 29

Question 29

Solubility and Solutions

9.8g of solid potassium chlorate (KClO3) were added to 40 cm3 of water and heated to dissolve all the solid. As the solution cooled, crystals of potassium chlorate started forming at 66°C. The solubility of potassium chlorate at 66°C is therefore

  1. A.24.5 moles per dm3
  2. B.0.2 moles per dm3
  3. C.10.0 moles per dm3
  4. D.20.0 moles per dm3
  5. E.2.0 moles per dm3.
Show the answer and explanation

Answer: E (2.0 moles per dm3.)

Explanation

At 66°C the solution is just saturated: 9.8 g in 40 cm3 = 245 g per dm3. Dividing by KClO3 = 122.5 g/mol gives 2.0 mol dm−3.