Question

Polyethylene is a synthetic polymer or plastic with many uses. 1.44 g of a polyethylene sample was dissolved in enough benzene to make 100. mL of soln, and the osmotic pressure was found to be 1.86 torr at 25 oC. What is the approximate molar mass of the polyethylene?

Answer 1

Solution :-

osmotic pressure = 1.86 torr

1.86 torr * 1 atm / 760 torr = 0.002447 atm

using the osmotic pressure we can calculate the molarity of the solution

= MRT

= osmotic pressure

M= molarity

R= constant 0.08206 L atm per mol K

T= kelvin temperature

M= /RT

   = 0.002447 atm / 0.08206 L atm per mol K * 298 K

   = 0.0001 M

now using the molarity and volume lets calculate the moles of the polymer

moles = molarity * volume in liter

         = 0.0001 mol per L * 0.100 L

         = 0.00001 mol

now using the mass and moles we can calculate the molar mass

molar mass = mass / moles

                 = 1.44 g / 0.00001 mol

                = 1.44*10^5 g/mol

So the molar mass of the polymer is 1.44*10^5 g/mol