Question

The average formula for low molecular mass starch is (C6H10O5)200. When 0.789g of starch is dissolved to make 100.0 mL of solution, what is the Osmotic pressure, in mmHg at 25 celsius?

Answer 1

mole = mass / molar mass

          = 0.789 g / 200 g / mole

         = 3.945 x 10^-3

volume = 100 mL = 0.1 L

molarity = moles / volume = 3.945 x 10^-3 / 0.1

           = 0.03945 M

temperature = 25 + 273 = 298 K

Osmotic pressure   = M R T

                             = 0.03945 x 0.0821 x 298

                             = 0.965 atm

                           = 0.965 x 760 mm Hg

                          = 734 mmHg

Osmotic pressure   = 734 mmHg