Question

3(b) The table below gives the solubility of salt Z at various temperatures.
Temperature(°C): 0,10,20,30,40,50,60 | Solubility(moldm⁻³): 0.13,0.21,0.31,0.45,0.63,0.85,1.10
(i) Plot a graph of solubility against temperature. (ii) From the graph determine the solubility of salt Z at 35°C. (iii) If 100cm³ of the saturated solution is cooled from 55°C to 35°C, calculate the mass of salt Z that would crystallize out. [Molar mass of salt Z = 100 g mol⁻¹]

Accepted Answer

(ii) The solubility of Z at 35°C is about 0.525 moldm⁻³ (read from the graph).
(iii) Mole at 35°C = (0.525x100/1000) = 0.0525 mol. Mole at 55°C = (0.65x100/1000) = 0.0965 mol. Amount crystallized = 0.0965-0.0525 = 0.044 mol. Mass = 0.044 x 100 = 4.4 g.

WAEC Chemistry 2011 Theory — Question 13

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