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12.33.    A sample of 0.50 g of an organic compound was treated according to Kjeldahl’s method. The ammonia evolved was absorbed in 50 ml of 0.5 M H_{2}SO_{4}. The residual acid required 60 mL of 0.5 M solution of NaO\! H for neutralisation. Find the percentage composition of nitrogen in the compound.

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Given that,
total mass of organic compound = 0.50 g
60 mL of 0.5 M solution of NaOH  required for neutralisation by residual acid.

60 mL of 0.5 M  NaOH solution = \frac{60}{2}  mL of 0.5M  H_{2}SO_{4} = 30 mL of 0.5 M H_{2}SO_{4}

Therefore,
Acid consumed in absorption of evolved ammonia is (50-30) mL = 20 mL

Again, 20 mL of 0.5 M H_{2}SO_{4} = 40 mL of 0.5 M NH_3

Also, since 1000 mL of 1 M NH_3 contains 14 g of nitrogen,
So,  40 mL of 0.5 M  NH_3 will contain = \frac{14\times 40\times 0.5}{1000} = 0.28 g of Nitrogen

Therefore, percentage(%) of nitrogen in 0.50 g of organic compound  = (0.28/0.5)\times 100 = 56 %

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