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JAMB Chemistry 2018 Paper

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Question : 31

Total: 87

What is the concentration of a solution containing 2g of NaOH in 100cm3 of solution? [Na = 23, O =16, H = 1]

0.40 moldm $^{-3}$
0.50 moldm $^{-3}$
0.05 moldm $^{-3}$
0.30 moldm $^{-3}$

Solution:

Concept:

Concentration in

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

is the number of moles of solute per cubic decimetre of solution.

Explanation:

Molar mass of

\mathrm{NaOH} = 23 + 16 + 1 = 40\ \mathrm{g\,mol^{-1}}

.

Moles of

\mathrm{NaOH} = \frac{2\ \mathrm{g}}{40\ \mathrm{g\,mol^{-1}}} = 0.05\ \mathrm{mol}

.

Volume

= 100\ \mathrm{cm^3} = 0.1\ \mathrm{dm^3}

.

Concentration

= \frac{0.05\ \mathrm{mol}}{0.1\ \mathrm{dm^3}} = 0.50\ \mathrm{mol\,dm^{-3}}

.

Answer:

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

(Option B)

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