Question

Determine the amount of urea (NH2CONH2) to be added in 1000 g of water to decrease its vapour pressure by 25%.

Answer 1

The correct answer is 1111
$\frac{P^{o}-P_{S}}{P^{o}}=\frac{n}{N+n}=\frac{1}{4}$
$\Rightarrow$4n = N+n
n=$\frac{N}{3}$=($\frac{1000}{18})$x$\frac{1}{3}$
Therefore, the amount of urea is $\frac{1000}{18\times 3}$x60 = $\frac{10000}{9}$gm
$\cong$ 1111.1 gram