To determine the percentage of nitrogen using the Kjeldahl's method, we first need to find out how much ammonia (NH3) was produced and then calculate the equivalent amount of nitrogen in the sample.
The ammonia released reacts with sulfuric acid (H2SO4) in the following stoichiometry :
2NH3+H2SO4→(NH4)2SO4
Each mole of H2SO4 reacts with 2 moles of NH3. Since 10 mL of 2 M sulfuric acid is neutralized by the ammonia, we can calculate the amount (in moles) of ammonia :
n(NH3)=2×n(H2SO4)
Now calculate the moles of H2SO4 used :
n(H2SO4)=M×V
n(H2SO4)=2M×10mL×1000mL1L
n(H2SO4)=0.02mol
Therefore, the number of moles of NH3 released will be twice that of the moles of H2SO4 neutralized :
n(NH3)=2×0.02mol
n(NH3)=0.04mol
Next, we use the molar mass of nitrogen (14 g/mol) to find the mass of nitrogen :
m(N)=n(N)×M(N)
m(N)=0.04mol×14g/mol
m(N)=0.56g
To find the percentage of nitrogen in the compound, we take the mass of nitrogen divided by the mass of the original sample and multiply by 100% :
Percentnitrogen=(m(sample)m(N))×100%
Percentnitrogen=(1g0.56g)×100%
Percentnitrogen=56%
The percentage of nitrogen in the compound is 56%.
