Question

Consider two solutions, one formed by adding 10 g of glucose (C6H12O6) to 1 L of water and the other formed by adding 10 g of sucrose (C12H22O11) to 1 L of water.

A. Calculate the vapor pressure for the first solution at 20 ∘C . (The vapor pressure of pure water at this temperature is 17.5 torr .)

B. Calculate the vapor pressure for the second solution at 20 ∘C . (The vapor pressure of pure water at this temperature is 17.5 torr .)     

Thank you

Answer 1

A)

moles of glucose = 10 / 180 = 0.056

moles of water = 1000 / 18 = 55.56

total moles = 0.056 + 55.56 = 55.6

mole fraction of glucose Xg = moles of glucose / total moles = 0.056 / 55.6

                                            = 0.00101

Po - Ps / Po = Xg

17.5 - Ps / 17.5 = 0.00101

Ps = 17.48 torr

vapor pressure for the first solution = 17.48 torr

B)

moles of sucrose = 10 / 342 = 0.0292

moles of water = 1000 / 18 = 55.56

total moles = 0.0292 + 55.56 = 55.59

mole fraction of glucose Xs = moles of glucose / total moles = 0.0292 / 55.58

                                            = 5.25 x 10^-4

Po - Ps / Po = Xg

17.5 - Ps / 17.5 = 5.25 x 10^-4

Ps = 17.49 torr

vapor pressure for the secong solution = 17.49 torr