WAEC Chemistry 2020 Paper

Concept:When a solution is diluted, the amount of solute remains constant, so the dilution equation $M_1 V_1 = M_2 V_2$ applies.Explanation:Here, $M_1$ is the initial concentration and $V_1$ is the initial volume.$M_2$ is the final concentration after dilution and $V_2$ is the final volume.Given: $M_1 = 0.200\ \mathrm{mol\ dm}^{-3}$ and $V_1 = 5.0\ \mathrm{cm}^{3}$.After dilution, the total volume is $V_2 = 250\ \mathrm{cm}^{3}$.Substitute these values into $M_1 V_1 = M_2 V_2$:$0.200 \times 5.0 = M_2 \times 250$.Simplify: $1.0 = 250 M_2$.Therefore, $M_2 = \frac{1.0}{250} = 0.004\ \mathrm{mol\ dm}^{-3}$.This matches option A.Answer: Option A: $0.004\ \mathrm{mol\ dm}^{-3}$.