Question

For the estimation of nitrogen, 1.4 g of an organic compound was digested by Kjeldahl method and the evolved ammonia was absorbed in 60 mL of M/10 sulphuric acid. The unreacted acid required 20 Ml of M/10 sodium hydroxide for complete neutralization. The percentage of nitrogen in the compound is
A. 0.05
B. 0.06
C. 0.1
D. 0.03

Answer 1

Correct Answer - C
Volume of the acid taken = 60 mL of M/10 `H_(2)SO_(4)`
Let the acid left unused
= v mL of M/10 `H_(2)SO_(4)`
Volume of M/10 NaOH used to neutralize the unreacted acid = 20mL
Applying molarity equation,
`underset("(Acid)")(n_(a)M_(a)V_(a)) = underset("(Base)")(n_(b)M_(b)V_(b))`
where `n_(a), M_(a)` and `V_(a)` are the basicity, molarity and volume of the acid and `n_(b), M_(b)` and `V_(b)` are the acidity, molarity and volume of the base
or `2 xx (1)/(10) xx v = 1 xx (1)/(10) xx 20`
`:. v = 10 mL`
`:.` Volume of the acid used = 60 - 10
= 50 mL of M/10 `H_(2)SO_(4)`
Now % of N
`= (1.4 xx "Molarity" xx "Volume" xx "Basicity of the acid used")/("Weight of the substance taken")`
`= (1.4 xx 1 xx 50 xx 2)/(10 xx 1.4) = 10.0`