WAEC Chemistry 2015 Theory — Question 45
Question 45 of 49 from the West African Examinations Council (WAEC) Chemistry 2015 Theory paper, with the correct answer and a full explanation.
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5(b)(iii). A salt Z of mass 10.2 g was dissolved in 15.4cm³ of distilled water at 40°C. Calculate the solubility of Z in mol/dm³ at 40°C. [MM (Z) = 331]
Model answer
Moles of Z = mass/molar mass = 10.2/331 = 0.0308 mol. Volume = 15.4 cm³ = 0.0154 dm³. If 0.0308 mol is present in 0.0154 dm³, then 1 dm³ would hold (0.0308/0.0154) = 2 mol. Thus, the solubility of Z at 40°C is 2 mol/dm³.
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