Test Index

WAEC Chemistry 2018 Paper

Question : 13

Total: 50

\mathrm{cm}^{3}

\mathrm{moldm}^{-3}

\mathrm{H}_2\mathrm{SO}_4

? ( H = 1, S = 32.0, O=16.0)

Solution:

Concept:

The amount of solute in moles is found by multiplying molar concentration by volume in

\mathrm{dm}^{3}

, then converted to mass using molar mass.

Explanation:

Convert volume to

\mathrm{dm}^{3}

500\,\mathrm{cm}^{3} = 0.5\,\mathrm{dm}^{3}

Moles of

\mathrm{H}_2\mathrm{SO}_4

= concentration

\times

volume =

0.005\,\mathrm{mol\,dm}^{-3} \times 0.5\,\mathrm{dm}^{3} = 0.0025\,\mathrm{mol}

Calculate molar mass of

\mathrm{H}_2\mathrm{SO}_4

2(1) + 32 + 4(16) = 98\,\mathrm{g\,mol}^{-1}

Mass = moles

\times

molar mass =

0.0025\,\mathrm{mol} \times 98\,\mathrm{g\,mol}^{-1} = 0.245\,\mathrm{g}

Answer:

0.245\,\mathrm{g}

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