Question

The usefulness of a fertilizer depends upon percentage of nitrogen present in it. Find which of the following is a better fertilizer:
(a) ammonium nitrate [NH₄NO₃]
(b) ammonium phosphate [(NH₄)₃PO₄]
(N = 14, H = 1, O = 16, P = 31)

Answer 1

(a) Molecular mass of ammonium nitrate [NH₄NO₃] = [14 + (1 $\times$ 4) + 14 + (3 $\times$ 16)] g = 80 g
Mass of nitrogen in ammonium nitrate [NH₄NO₃] = (14 + 14) = 28 g
$\mathrm{Percentage}\mathrm{of}\mathrm{N}=\frac{\mathrm{Mass}\mathrm{of}\mathrm{N}\mathrm{in}\mathrm{the}\mathrm{compound}}{\mathrm{Molecular}\mathrm{mass}\mathrm{of}{\mathrm{NH}}_4{\mathrm{NO}}_3}\times 100=\frac{28}{80}\times 100=35$

(b) Molecular mass of ammonium phosphate [(NH₄)₃PO₄] = {[3$\times$(14 + (1 $\times$ 4)] + 31 + (4 $\times$16)} g = 149 g
Mass of nitrogen in ammonium phosphate [(NH₄)₃PO₄] = (14 $\times$ 3) g = 42 g
$\mathrm{Percentage}\mathrm{of}\mathrm{N}=\frac{\mathrm{Mass}\mathrm{of}\mathrm{N}\mathrm{in}\mathrm{compound}}{\mathrm{Molecular}\mathrm{mass}\mathrm{of}{\left({\mathrm{NH}}_4\right)}_3{\mathrm{PO}}_4}\times 100=\frac{42}{149}\times 100=28.2$

Percentage of nitrogen is higher in ammonium nitrate; hence, it is a better fertiliser than ammonium nitrate.