Percentage composition of fertilisers

As with metal ores, it is useful to be able to calculate exactly what proportion the essential nutrients accounts for in a fertiliser.

Question

Ammonium nitrate (NH4NO3) is commonly used as a fertiliser. Given the relative atomic mass of hydrogen is 1, nitrogen is 14 and oxygen is 16, calculate the percentage of ammonium nitrate that is nitrogen.

Begin by calculating the formula mass.

Ammonium nitrate NH4NO3. Nitrogen atom formula mass 14g, 4 hydrogens of 4g, one nitrogen 14g and three oxygen 48g. NH4NO3 formula mass is therefore 14 plus 4 plus 14 plus 48, which equals 80g.

The percentage of ammonium nitrate that is nitrogen is given by the formula:

\[\% \,of\,N\,in\,N{H_4}N{O_3} = \frac{{mass\,of\,N\,in\,N{H_4}N{O_3}\,}}{{formula\,mass\,of\,N{H_4}N{O_3}}} \times 100\]

\[\begin{array}{l} = \frac{{28}}{{80}} \times 100\\ = 35\% \end{array}\]

Ammonium nitrate is 35 per cent nitrogen.

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