MCQ Detailed View

Potassium nitrate (KNO₃) is a common inorganic salt widely used in fertilizers, food preservation, and pyrotechnics. To calculate the percentage composition of any compound, the molecular (molar) mass of the entire compound is compared to the atomic mass of the specific element of interest—in this case, nitrogen (N).

The molecular mass of KNO₃ is calculated as follows:

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  Potassium (K) = 39 g/mol

  
  


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  Nitrogen (N) = 14 g/mol

  
  


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  Oxygen (O) = 16 g/mol × 3 = 48 g/mol

  
  

Total molar mass of KNO₃ = 39 + 14 + 48 = 101 g/mol.

Now, the contribution of nitrogen in this compound is only 14 g (from the one nitrogen atom present). To find the percentage, we apply the formula:

%N=Mass of N in compoundMolar mass of compound×100\%N = \frac{\text{Mass of N in compound}}{\text{Molar mass of compound}} \times 100%N=Molar mass of compoundMass of N in compound×100 %N=14101×100=13.86%\%N = \frac{14}{101} \times 100 = 13.86\%%N=10114×100=13.86%

Thus, the percentage of nitrogen in potassium nitrate is 13.86%, which matches option C.

This type of calculation is part of analytical chemistry and is fundamental for determining the composition of chemical compounds. In the fertilizer industry, the nitrogen percentage is especially important because it directly relates to the nutrient value provided to plants. Potassium nitrate, being a double nutrient fertilizer, provides both potassium (K) and nitrogen (N) in readily available forms.

For comparison, other nitrogen-containing compounds like ammonium nitrate (NH₄NO₃) have a much higher nitrogen content (~35%), while urea (CO(NH₂)₂) contains about 46% nitrogen, making them more concentrated nitrogen sources than KNO₃.

Hence, the correct answer is 13.86%, making potassium nitrate a moderate nitrogen fertilizer.