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WAEC Chemistry 2016 Paper

Question : 31

Total: 50

Solution:

Concept:

Solubility is the amount of solute in moles dissolved in

1\,\mathrm{dm}^3

of a saturated solution.

Explanation:

The saturated solution volume is

350\,\mathrm{cm}^3

Mass of salt Z obtained is

55.5\,\mathrm{g}

and its molar mass is

101\,\mathrm{g\,mol}^{-1}

Moles of salt Z:

\text{moles} = \dfrac{55.5}{101} = 0.55\,\mathrm{mol}

Thus,

350\,\mathrm{cm}^3

of the solution contains

0.55\,\mathrm{mol}

of Z.

Convert volume to

\mathrm{dm}^3

350\,\mathrm{cm}^3 = 0.35\,\mathrm{dm}^3

Solubility

= \dfrac{0.55}{0.35} = 1.57\,\mathrm{mol\,dm}^{-3}

Answer:

1.57\,\mathrm{mol\,dm}^{-3}

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