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WAEC Chemistry 2016 Paper

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Question : 7

Total: 50

The mass of potassium hydroxide required to make 300.ocm³ of 0.4 moldm^-3 solution is {KOH = 56.0}

26.88g
13.44g
6.72g
3.36g

Solution:

Concept:

Use the relationship between concentration, volume, and molar mass to find the required mass.

Explanation:

Convert volume to

\mathrm{dm}^3

:

300\,\mathrm{cm}^3 = 0.300\,\mathrm{dm}^3

.

Calculate moles of KOH:

n = C \times V = 0.4 \times 0.300 = 0.12\,\mathrm{mol}

.

Mass

= n \times \text{molar mass} = 0.12 \times 56.0 = 6.72\,\mathrm{g}

.

Answer:

6.72\,\mathrm{g}

(Option C).

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