The p-Block Elements

The p-Block Elements

Question

29.5 mg of an organic compound containing nitrogen was digested according to Kjeldahl’s method and the evolved ammonia was absorbed in 20 mL of 0.1 M HCl solution. The excess of the acid required 15 mL of 0.1 M NaOH solution for complete neutralization. The percentage of nitrogen in the compound is

  • 59.0

  • 47.4

  • 23.7

  • 29.5

Answer

C.

23.7

m moles of HCl = 20 × 0.1 = 2
m moles of NaOH = 15 × 0.1 = 1.5
∴ m moles of HCl that consumed NH3 = 0.5
m moles of NH3 = 0.5
milligrams of N in NH3 = 0.5 × 14 = 7 mg
percent sign space of space straight N space equals space fraction numerator 7 over denominator 29.5 end fraction space straight x space 100 space equals space 23.7 percent sign

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