Question : The percentage of nitrogen present in ammonium sulphate is:
Option 1: 21%
Option 2: 25%
Option 3: 30.5%
Option 4: 18%
Correct Answer: 21%
Solution : The correct option is 21%.
According to the chemical formula of ammonium sulphate (NH
4
)
2
SO
4
), each molecule of ammonium sulphate includes two ammonium ions (NH
4+
). One nitrogen atom (N) is present in each ammonium ion (NH
4+
). The molar mass of nitrogen and the molar mass of ammonium sulphate may be used to calculate the proportion of nitrogen in ammonium sulphate: Nitrogen (N) molar mass is about 14 grams/mol. Ammonium sulphate [NH
4
)
2
SO
4
] molar mass: (2 NH
4
+
ions) + (1 SO
4
-
2
ion); (2 ×18 g/mol for NH
4
+
) + (1 × 96 g/mol for SO
4
-
2
); 36 g/mol plus 96 g/mol = 132 g/mol; the percentage of nitrogen in ammonium sulphate: (2 × Molar mass of nitrogen) / Molar mass of ammonium sulfate; (2 × 14 g/mol) / 132 g/mol; (28 g/mol) / (132 g/mol) ≈ 0.2121
To express this as a percentage, multiply by 100:
0.2121 × 100 ≈ 21.21%
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