Question

0.6% solution of urea and 1.8% solution containing a solute A are isotonic with each other. calculate the molecular weight of the solute A

Answer 1

Answer: 180 g/mol

Explanation:- Isotonic solutions are those solutions which have the same osmotic pressure.

$\pi =CRT$ if osmotic pressures are equal at the same temperature, concentrations must also be equal.

$\pi$ = osmotic pressure

C= concentration

R= solution constant

T= temperature

Thus: $C_{urea}=C_A$ where concentration is in molarity.

For urea solution: 0.6 g of urea is dissolved in 100 ml of solution.

For solute A: 1.8 g of A is dissolved in 100 ml of solution.

$Molarity=\frac{\text{Mass of solute}\times 1000}{\text{Molar mass of solute}\times \text{volume of solution in ml}}$

$C_{urea}=\frac{0.6\times 1000}{60}\times {100}=0.1$

$C_ A=\frac{1.8\times 1000}{M_A}\times 100$

As $C_{urea}=C_A$

$0.1=\frac{1.8\times 1000}{M_A}\times 100$

$M_A= 180g/mol$