Question

Which of the following sets of solutions of urea (mol. mass 60 g mol^-1) and sucrose (mol. mass 342 g mol^-1) is isotonic?

Options

• 9.1 gL^-1 urea and 6.0 gL^-1 sucrose

• 3.0 gL^-1 urea and 3.0 gL^-1 sucrose

• 6.0 gL^-1 urea and 9.0 gL^-1 sucrose

• 3.0 gL^-1 urea and 17.1 gL^-1 sucrose

Answer 1

3.0 gL^-1 urea and 17.1 gL^-1 sucrose

Explanation:

Isotonic solutions are those solutions which have same osmotic pressure at a given temperature.

Formula for osmotic pressure, π = CRT

Considering the set given in option (d), I.e. 3.0 gL^-1 urea and 17.1 gL^-1 sucrose.

Given, molecular mass of urea 60 g mol^-1 and molecular mass of sucrose 342 g mol^-1.

For urea,

conc. C = `3/60 = 1/20`

Osmotic pressure π₁ = `1/20 xx "R" xx "T"`

For sucrose cone. C = `17.1/342 = 1/20`

∴ Osmotic pressure, π₂ = `1/20`RT

Thus, set of solution of urea and sucrose given in 4th option is isotonic.