Question

1.216 g of an organic compound was Kjeldahlised and the ammonia evolved was absorbed in 100 mL of 1-N `H_(2)SO_(4)`. The remaining acid solution was made upto 500 mL by dilution with water. 20 mL of this diluted solution required 32 mL of `N//10 NaOH` solution for complete neutralisation. calculate the percentage of nitrogen in the compound.

Answer 1

Step I. Calculation of the normality of diluted `H_(2)SO_(4)` solution.
Volume of `NaOH` solution = 32 mL
Normality of `NaOH` solution `= N//10`
Volume of the `H_(2)SO_(4)` solution `= 20` mL
Normality of `H_(2)SO_(4)` solution can be calculated by applying normality equation
`ubrace(N_(1)V_(1))_("Acid")= ubrace(N_(2)V_(2))_("Base")`
`Nxx20=1/10xx32, N=32/(10xx20)`
Step II. Calculation of the volume of unused `H_(2)SO_(4)`
`ubrace(N_(1)V_(1))_("Conc. acid")= ubrace(N_(2)V_(2))_("Diluted acid")`
`1xxV=(32xx500)/(10xx20)=80 mL`.
Step III. Calculation of the volume of used `H_(2)SO_(4)`
Total volume of `H_(2)SO_(4)` yaken = 100 mL
Volume of `H_(2)SO_(4)` unused = 80 mL
Volume of `H_(2)SO_(4)` used `100-80=20` mL.
Step IV. Calculation of the percentage of nitrogen.
Percentage of `(1.4xx"Normality of acid used"xx"Volume of acid used")/("Mass of the compound")`
`=(1.4xx1xx20)/(1.216)=23.03 %`