Question

A saturated solution is made by dissolving 0.252 g of a polypeptide (a substance formed by joining together in a chainlike fashion some number of amino acids) in water to give 1.92 L of solution. The solution has an osmotic pressure of 3.69 torr at 25 °C. What is the approximate molecular mass of the polypeptide?

pi=3.69/760torr =.00485
M= m? r= .08205
T= 25+273.15= 298.15
m= pi/rt= .0000162 x 1.92=.0000312
.2521/.0000312
I get 8080.128 does that seem right?

Answer 1

The procedure looks ok but the numbers don't.You must be punching the wrong buttons.
The 0.00485 is really 0.004855 and I would round that to 0.00486
M (and that's M and not m) = 0.000198 x 1.92 = 0.000381
and molar mass is 0.242/0.000381 = ?
Check my work.