Question

A solution is prepared by dissolving 0.822 g of it in 300mdm of water which has osmotic pressure of
149 mm Hg at 298 K. The molar mass of substance is
(a) 3.42 g mol
(b)34.2g molt
(C)342 g mol (d) 3420 g mol​

Answer 1

Given info : A solution is prepared by dissolving 0.822 g of it in 300 cm³ of water which has osmotic pressure of 149 mm Hg at 298K.

To find : The molar mass of substance is ...

solution : using formula, π = CRT

where π is osmotic pressure,

C is concentration of solute in solution.

R is gas constant.

and T is temperature in Kelvin.

π = 149 mm Hg = 149/760 atm

R = 0.082 L.atm/mol/K

T = 298 K

so, 149/760 = C × 0.082 × 298

⇒C = 0.008

C = mole of solute/volume of solution in L

⇒0.008 = n/0.3 L

⇒n = 0.0024

⇒mass of solute/molar mass of solute = 0.0024

⇒molar mass of solute = 0.822/0.0024 = 342.5g this is nearest value of 342 g/mol

Therefore the molar mass of substance is 342g/m.