Question

What is the percentage of nitrogen in an organic compound, $0.14$ g of which gave by Dumas method, $82.1$ cc of nitrogen collected over water at ${27}^{o}C$ and at a barometric pressure of $774.5$ mm? (aqueous tension of water at ${27}^{o}C$ is $14.5$ mm)

• A. 64.1
• B. 58.7
• C. 77.9
• D. 66.7

Answer 1

The correct option is D 66.7

$\frac{PV}{T}=\frac{P^{\prime }{V}^{\prime }}{T^{\prime }}$
$\frac{760\times V}{273}=\frac{(774.5-14.5)\times 82.1}{298}$
$V=75.2cc$
Weight of 75.2 cc of nitrogen at STP $=\frac{28\times 75.2}{22400}=0.094g$
Percentage of nitrogen $\frac{0.094}{0.14}\times 100=66.7$%.