A solution of sodium trioxocarbonate (IV) contains 10.6g in 250cm 3 of solution. Calculate the concentration of the solution. [Na 2 CO 3 = 106.0]

Correct Answer is : 0.4 mol dm-3

Correct Answer is : 0.4 mol dm-3

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WAEC Chemistry 2010 Paper

Question : 12

Total: 38

Solution:

Concept:

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

Explanation:

Given mass of

\mathrm{Na}_{2}\mathrm{CO}_{3} = 10.6\,\mathrm{g}

and molar mass

= 106.0\,\mathrm{g\,mol}^{-1}

Moles of

\mathrm{Na}_{2}\mathrm{CO}_{3} = \frac{10.6}{106.0} = 0.1\,\mathrm{mol}

Volume of solution

= 250\,\mathrm{cm}^{3}

Since

1\,\mathrm{dm}^{3} = 1000\,\mathrm{cm}^{3}

, convert the volume into

\mathrm{dm}^{3}

250\,\mathrm{cm}^{3} = 0.25\,\mathrm{dm}^{3}

Concentration

\displaystyle = \frac{\text{moles}}{\text{volume in }\mathrm{dm}^{3}} = \frac{0.1}{0.25} = 0.4\,\mathrm{mol\,dm}^{-3}

Answer:

The concentration of the solution is

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

. Hence, the correct option is A.

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