Question

What is the molecular weight of a polymer if 3.50g are dissolved in enough water to give 252 mL of the solution and give a osmotic pressure of 28.52 mm Hg at 25 degrees Celsius?

Answer 1

we know that

osmotic pressure = C x R x T

where

C = concentration

given

osmotic pressure = 28.52 mm Hg

osmotic pressure = 28.52 / 760 atm

osmotic pressure = 0.0375

now

temperature = 25 C = 298 K

so

0.0375 = C x 0.0821 x 298

C = 1.5338 x 10-3

now

we know that

concentration = moles of solute x 1000 / volume of solution (ml)

so

1.5338 x 10-3 = moles of solute x 1000 / 252

moles of solute = 3.865 x 10-4

now

moles = mass / molar mass

so

3.865 x 10-4 = 3.5 / molar mass

molar mass = 9055

so

the molecular weight of the polymer is 9055 g / mol