A `5.25%` solution of a substance is isotonic with a `1.5%` solution of urea (molar mass `= 60g mol^(-1)`) in the same solvent. If the densities of both the solutions are assumed to be equal to `1.0 g cm^(-3)`, molar mass of the substance will be:

Options

A. `210.0g mol^(-1)`
B. `90.0g mol^(-1)`
C. `115.0 g mol^(-1)`
D. `105.0 g mol^(-1)`

Answer

A

Explanation

isotonic solutions have same osmotic pressure
`pi_(1)=C_(1)RT, pi_(2)=C_(2)RT`
For isotonic solution `pi_(1)=pi_(2)`
`therefore C_(1)=C_(2)` or `(1.5)/((60)/(V))=(5.25)/((M)/(V))` [Where M = Molecular]
[Weight of the substance]
or `(1.5)/(60)=(5.25)/(M)` or `M = 210`