In Kjeldahl's method, 0.4422 g of an organic compound was digested with conc. `H_(2)SO_(4)`. The ammonia evolved on distilling the resulting solution with excess of `NaOH` solution was absorbed in 50 mL of 1 N `H_(2)SO_(4)` solution. The residual acid required 65.5 mL of `N//2` alkali solution for complete neutralisation. Find the percentage of nitrogen in the given organic compound.

Explanation

Calculation of the volume of unused acid.
volume of `NaOH` solution =65.5 mL
Normality of `NaOH` solution `=1//2 N`
Normality of `H_(2)SO_(4)` solution `= 1 N`
Volume of the acid can be calculated by applying normality equation,
`ubrace(N_(1)V_(1))_("Acid")= ubrace(N_(2)V_(2))_("Base")`
`(1N)xxV_(1)=(1//2N)xx(65.5 mL), V_(1)=((1//2N)xx(65.5 mL))/((1N))=32.75 mL`
Step II. Calculation of the volume of acid used
volume of `H_(2)SO_(4)` added =50 mL
Volume of `H_(2)SO_(4)` left unused =32.75 mL
`:.` Volume of `H_(2)SO_(4)` used `= (50-32.75)=17.25 mL`
Step III. Calculation of the percentage of nitogen
Mass of compound =0.4422 g
Volume of `H_(2)SO_(4)` used =17.25 mL
Normality of `H_(2)SO_(4)` used = 1 N
Percentage of `N=(1.4 xx" Volume of acid used"xx"Normality of acid used")/("Mass of the compound")`
`=(1.4xx17.25xx1)/0.4422=54.61 %`