Consider a solution of 6.84 g of sugar (sucrose, C12H22O11) in 90.0 g of water. a. Calculate the number of moles of sugar and water present. (H=1; C=12; O=16) b. Calculate the mole fraction of the water in the solution. c. At 100°C, the saturated vapour pressure of water at its boiling point is 101325 Pa. Calculate the vapour pressure of the solution at that temperature. d. Would the solution of sugar in water boil at this temperature, assuming the external pressure remains at 101325 Pa? Explain your answer.
1. Consider a solution of 6.84 g of sugar (sucrose, C12H22O11) in 90.0 g of water.
a. Calculate the number of moles of sugar and water present. (H=1; C=12; O=16)
b. Calculate the mole fraction of the water in the solution.
c. At 100°C, the saturated vapour pressure of water at its boiling point is 101325 Pa.
Calculate the vapour pressure of the solution at that temperature.
d. Would the solution of sugar in water boil at this temperature, assuming the external
pressure remains at 101325 Pa? Explain your answer.
2. Calculate the vapour pressure in torr of a solution that is made by dissolving 59.51 grams of
glucose (C6H12O6) in 112.2 mL of water at 26.7 oC. The vapour pressure of pure water at 26.7 oC
is 26.271 torr and the density of water at that temperature is 0.99669 g/mL.
3. At a given temperature, you have a mixture of ethanol (vapour pressure of pure ethanol
= 59.02 torr) and methanol (vapour pressure of pure methanol = 127.2 torr). The mole fraction of
ethanol in the solution is 0.724. Assuming ideal behavior, calculate the mole fraction of methanol
in the vapour above the solution.
4. A benzene toluene solution with χ benzene = 0.3 has a normal boiling point of 98.6 oC. The
vapour pressure of pure toluene at 98.6 oC is 533mmHg. Assuming ideal solution behaviour,
what must the vapour pressure of pure benzene be at 98.6 oC?
5. The vapour pressure of pure hexane and pentane at 25oC are 149.1mmHg and 508.5mmHg
respectively. If a hexane pentane solution has a mole fraction of hexane of 0.75, what are the
vapour pressures of hexane and pentane above the solution? What is total vapour pressure?
6. A solution has a 1:3 ratio of cyclopentane to cyclohexane. The vapour pressures at 25 °C are 331
mmHg for pure cyclopentane and 113 mmHg for pure cyclohexane. What is the mole fraction of
cyclopentane in the vapour above the solution?
7. The vapour pressure above a solution of two volatile components is 745 Torr and the mole
fraction of component B (χB) in the vapour is 0.59. Calculate the mole fraction of B in the liquid
if the vapour pressure of pure B is 637 Torr.
8. A solution containing hexane and pentane has a pressure of 252.0 Torr. Hexane has a pressure at
151.0 Torr and pentane has a pressure of 425.0 Torr. What is the mole fraction of pentane?
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