What is the osmotic pressure, expressed in the unit mmH2O, of a solution containing 125 ug of vitamin B12 (C63H88CoN14O14P) in 2.50 mL H2O at 25 degrees C?
Answer: 9.33 mmH2O
pi = MRT
Convert ug vitamin B12 to mols mols = grams/molar mass.
Then mol/L = M and substitute into the first equation and solve for pi in atm.
Here is a site to convert atm to H2O.
http://www.aqua-calc.com/convert/pressure/atmosphere