WAEC Chemistry 2020 Paper

Concept:Solubility is expressed as the amount of solute in moles dissolved in one cubic decimetre of solution, giving the unit $\mathrm{mol\,dm^{-3}}$.Explanation:Convert the volume of the saturated solution from $\mathrm{cm}^3$ to $\mathrm{dm}^3$.$250\,\mathrm{cm}^3 = 0.250\,\mathrm{dm}^3$Calculate the number of moles of $\mathrm{CuSO}_4$ dissolved in the solution.Moles $= \frac{\text{mass}}{\text{molar mass}} = \frac{5.0}{160} = 0.03125\,\mathrm{mol}$Now find the solubility by dividing the moles of solute by the volume of solution in $\mathrm{dm}^3$.Solubility $= \frac{0.03125}{0.250} = 0.125\,\mathrm{mol\,dm^{-3}}$Answer:Option B: $0.125$