JAMB Chemistry 2024 Paper

Concept:Solubility is the concentration of a saturated solution, expressed as moles of solute per cubic decimetre of solution.Explanation:Use the formula: $Solubility = \frac{\text{number of moles of solute}}{\text{volume of solvent in dm}^3}$.First, calculate the number of moles of potassium chloride ($\mathrm{KCl}$).Molar mass of $\mathrm{KCl} = 39 + 35.5 = 74.5 \, \mathrm{g\,mol}^{-1}$.Mass of solute $= 25.0 \, \mathrm{g}$.Moles of $\mathrm{KCl} = \frac{25.0}{74.5} = 0.336 \, \mathrm{mol}$.Since the density of water is approximately $1 \, \mathrm{g\,cm}^{-3}$, $80 \, \mathrm{g}$ of water occupies $80 \, \mathrm{cm}^3 = 0.080 \, \mathrm{dm}^3$.Now, calculate the solubility: $Solubility = \frac{0.336 \, \mathrm{mol}}{0.080 \, \mathrm{dm}^3} = 4.2 \, \mathrm{mol\,dm}^{-3}$.Answer:$4.2 \, \mathrm{mol\,dm}^{-3}$ — Option D.