Question

A solution is made by dissolving 5.61 g of a new polymer in enough water to make 260 mL of solution. At 25.0 oC, the osmotic pressure of the solution is 0.174 atm. What is the molar mass of the polymer in g/mol? (Use the E symbolism. e.g., 3123 would be 3.123E3 with 3 significant figures - i.e., 2 after the decimal point.)

Answer 1

Osmotic pressure is given by :

= MRT

where M is the molarity

R is the gas constant = 0.0821 L.atm/mol.K

Temperature(T) = 25^oC = 25+ 273 = 298 K

and is the osmotic pressure = 0.174 atm

So, 0.174 atm = M * 0.0821 L.atm/mol.K * 298 K

M = 0.007112 mol/ L

Now, Molarity = Moles / Volume = Mass of protein /Molar mass of protein *Volume

0.007112 mol/ L = 5.61 g /( Molar mass of protein * 0.260L)

Molar mass of protein = 3.03E3 g/mol