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JAMB Chemistry 2010 Paper

Question : 2

Total: 49

[Ca = 40, N = 14, O = 16]

Solution:

Concept:

Percentage by mass is the mass of nitrogen in one mole of the compound divided by the total molar mass, multiplied by

100\%

Explanation:

Calcium trioxonitrate(V) is

\mathrm{Ca(NO_3)_2}

Molar mass of

\mathrm{Ca(NO_3)_2}

\mathrm{Ca} = 40

2 \times \mathrm{N} = 2 \times 14 = 28

6 \times \mathrm{O} = 6 \times 16 = 96

Total molar mass

= 40 + 28 + 96 = 164

Mass of nitrogen in the compound is

28

Percentage by mass of nitrogen:

\frac{28}{164} \times 100\% = 17.073\%

This is approximately

17.1\%

Answer:

17.1\%

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