Question

A solution of urea is isotonic with 12 g/L glucose solution at 300 K.The concentration of urea is _____.

• A. 4 g/L
• B. 12 g/L
• C. 16 g/L
• D. 1 g/L

Answer 1

Answer: (A)

4 g/L

Isotonic solutions are those which have same osmotic pressure

We have,

$\pi =\frac{n}{V}RT$

where $\pi =$ Osmotic pressure

$c=\frac{n}{V}=$ concentration

$n=$ number of moles

$R=$ Gas constant

$T=$ Temperature

So, ${\pi }_{urea}={\pi }_{glucose}$

$\frac{n_{urea}}{V}RT=\frac{n_{glucose}}{V}RT$

$\frac{n_{urea}}{V}=\frac{n_{glucose}}{V}$

$n_{urea}=n_{glucose}$

$\frac{Mas{s}_{urea}}{Molecularmas{s}_{urea}}=\frac{Mas{s}_{glucose}}{Molecularmas{s}_{glucose}}$

$\frac{M}{60}=\frac{12}{180}$

$M=4g$

Thus concentration of urea $=4g/L$