(a) A certain aqueous solution of sucrose at 25°C has a vapor pressure of 23.34

Question

(a) A certain aqueous solution of sucrose at 25°C has a vapor pressure of 23.34 torr. The vapor pressure of water at 25°C is 23.76 torr. Find the activity of the solvent water in this sucrose solution.

(b) A 1.00 mol/kg aqueous sucrose solution has a vapor pressure of 22.75 torr at 25°C. Find the activity and activity coefficient of the solvent water in this solution.

Please do not enter any units for activity, and activity coefficient (they are unitless)

Please enter the activity, and activity coefficient in 4 significant figures

Explanation / Answer

a) Use the following expression:

PH2O = aH2O * PºH2O

aH2O = 23.34 / 23.76 = 0.9823

b) The activity is calculated the same way of before:

aH2O = 22.75 / 23.76 = 0.9575

Now for the activity coeficient, we need the mole fraction of water:

If 1 mole of solution is in 1 kg of water or 1000 g then:

moles = 1000 / 18 = 55.56

mole fraction = 55.56 / 56.56 = 0.98

Ac = 0.9575 / 0.98 = 0.9770

Hope this helps

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