Q.

Following Kjeldahl's method, 1 g of organic compound released ammonia, that neutralised 10 mL of 2M H2SO4. The percentage of nitrogen in the compound is ______%.           [2024]


Ans.

(56)

    Millimoles of sulphuric acid (nH2SO4)=Molarity×volume in mL

    =2 M×10 mL=20 mmol

    Ammonia is a base, it reacts with sulphuric acid to form salt:

    2NH3+H2SO4→(NH4)2SO4

    By stoichiometry:

    nNH32=nH2SO41

    nNH32=20 mmol1

    nNH3=40 mmol=0.04 mol

    Moles of N (nN)=Moles of ammonia (nNH3)=0.04 mol

    Since amount of nitrogen is conserved, number of moles of N in organic compound (nN)=number of moles of N in ammonia 

    (nNH3)=0.04 mol

    Weight of N in organic compound (WN)=nN×Molar mass of N

    =0.04 mol×14 g mol-1=0.56 g

    Percentage of nitrogen in organic compound:

    =WNWcompound×100=0.561×100=56%