In Kjeldahl’s method for the estimation of nitrogen present in a soil sample, the ammonia evolved from 0.75g of sample neutralized 10mL of 1MH2SO4. The percentage of nitrogen in the soil is:
A
37.33
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B
45.33
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C
35.33
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D
43.33
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Solution
The correct option is A37.33 This can be solved on the basis of law of chemical equivalance
According to which; gramequivalentsofNH3=gramequivalentsofH2SO4 moles×nf=M×V×nf1000 →n×1=1×10×21000 →n=201000=2×10−2
Now,
1 mole of NH3 contains 1 mole of `N`. ∴2×10−2 moles of NH3 contains 2×10−2 moles of nitrogen.
Hence,
mass of `N `= moles× molar mass
= 2×10−2×14
= 0.28 g ∴ % of `N` =0.280.75×100