JAMB Chemistry 2012 Question 17

Question 17

Solubility and Solutions

Potassium trioxochlorate(V) has a solubility of 1.5 mol dm⁻³ at 45 °C. On cooling this solution to a temperature of 20 °C, the solubility was found to be 0.5 mol dm⁻³. What mass of KClO₃ was crystalized out? [K = 39, Cl = 35.5, O = 16]

A.1.00 g
B.10.00 g
C.12.25 g
D.122.50 g

Show the answer and explanation

Answer: D (122.50 g)

Explanation

1.5 − 0.5 = 1.0 mol crystallises from each dm³. KClO₃ = 122.5 g/mol, so 122.5 g crystallises (taking 1 dm³ of solution).