JAMB Chemistry 2011 Objective — Question 10

Question 10 of 49 from the Joint Admissions and Matriculation Board (JAMB) Chemistry 2011 Objective paper, with the correct answer and a full explanation.

[Diagram: number of moles of solute vs temperature graph] From the diagram above, find the amount of solute deposited when 200cm³ of the solution is cooled from 55°C to 40°C.

A. A. 0.02 mole
B. B. 0.10 mole
C. C. 0.20 moleCorrect
D. D. 0.01 mole

Explanation

From the graph, solubility at 55°C = 6 moldm⁻³ and at 40°C = 5 moldm⁻³. Mole present in 200cm³ at 55°C = (200/1000)x6 = 1.2 mole. Mole present at 40°C = (200/1000)x5 = 1.0 mole. Mole crystallized out = 1.2 - 1.0 = 0.2 mole.

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