Calculate the molar mass of the substance if a 5.25% solution of the substance is sisotonic with 1.5% solution of urea(molar mas `=60mol^(-1)`) in the same solvent. Assuming the densities of both the solutions is equal to `1.0gcm^(-3)`

Options

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

Answer

A

Explanation

Isotonic solutions have saem osmotic pressure
`pi_(1)=C_(1)RT,pi_(2)=C_(2)RT`
For isonic solutions the osmotic pressure is equal
So `pi_(1)=pi_(2):.C_(1)=C_(2)`
concentration `=("Number of moles")/("volume of soluton")`
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`