Question

i need some help with this i don't even know where to begin

A solution of 62.4 g of insulin in enough water to make 1.000 L of solution has an osmotic pressure of 0.305 atm at 25°C. Based on these data, what is the molar mass (MW) of insulin (g/mol)? (Which is the best answer below?)

a)621
b)5000
c)7570
d)71,900



You can start with the relationship of osmatic pressure to molarity.

Answer 1

You can use the known value of osmotic pressure (0.305 atm) to solve the equation pi=i(MRT) where (i) is Van 't Hoff factor (1 since insulin is not ionic) R is the constant 0.0821 L atm / K mol, and T is temperature in Kelvin. So solving you get:

0.305=1(0.08206)(298)
0.305=24.466M
M=0.125

since Molar mass is g/mol.

62.4g/0.012472mol= 5003g/mol or round to 5000g/mol inslulin

So answer is B 5000