Question

The available nitrogen in a urea sample is found to be 45% (by weight). Find the actual urea content in 560 g of the sample.

• A. 252 g
• B. 504 g
• C. 280 g
• D. 540 g

Answer 1

The correct option is D 540 g

The molecular formula of urea $=N{H}_{2}CON{H}_2$
So, in 60 g of urea, mass of nitrogen $=28g$.
% nitrogen = $\frac{28}{60}\times 100=46.66$%
The sample is impure.
According to the question, the mass of nitrogen in 560 g of the sample $=560\times \frac{45}{100}=252g.$
So, amount of urea when 252 g of nitrogen is present $=\frac{60}{28}\times 252=540g.$