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Question 1

The partial molar volumes of water, H₂O, and methanol, CH₃OH, are 17.8 cm³ mol^-1 and 38.4 cm³ mol^-1 respectively at 25.0°C for dilute mixtures of methanol in water. Calculate the total volume when 15 cm³ of methanol is added to 250 cm³ of water at this temperature. The density of methanol is 0.791 g cm^-3.

a) 265 cm³

b) 269 cm³

c) 261 cm³

d) 250 cm³

Question 2

Calculate the change in the chemical potential of a perfect gas when it expands isothermally at a temperature of 20.0°C so that its volume doubles.

a) -1.69 kJ mol^-1

b) -115 J mol^-1

c) +1.69 kJ mol^-1

d) +115 J mol^-1

Question 3

Calculate the entropy change when 2.0 mol of a perfect gas A and 3.0 mol of a perfect gas B mix spontaneously.

a) +195 J K^-1

b) +28 J K^-1

c) -12 J K^-1

d) -8.34 kJ K^-1

Question 4

Which of the following statements is always true for a liquid mixture of two components A and B in equilibrium with a mixture of their vapours?

a) μ_A(l) = μ_B(l) and μ_A(g) = μ_B(g)

b) μ_A(l) = μ_A(g) = μ_B(l) = μ_B(g)

c) μ_A(l) = μ_A(g) and μ_B(l) = μ_B(g)

d) μ_A(l) ≠ μ_A(g) ≠ μ_B(l) ≠ μ_B(g)

Question 5

A solution is prepared by dissolving 5.32 g of benzene, C₆H₆, in 93.2 g of toluene, C₆H₅CH₃, at 25°C. The vapour pressures of pure benzene and pure toluene are 12.7 kPa and 3.8 kPa at this temperature. Use Raoult's law to determine the partial vapour pressure of each of the two components for the mixture.

a) p_B = 0.68 kPa, p_T = 1.01 kPa

b) p_B = 0.06 kPa, p_T = 0.94 kPa

c) p_B = 77.9 kPa, p_T = 23.3 kPa

d) p_B = 0.80 kPa, p_T = 3.56 kPa

Question 6

The vapour pressure of bromobenzene, C₆H₅Br, above an ideal-dilute aqueous solution of molality 0.092 mol kg^-1 is 23.6 kPa. Calculate the Henry's law constant of bromobenzene.

a) 256 kPa kg mol^-1

b) 2.17 kPa kg mol^-1

c) 461 Pa kg mol^-1

d) 390 Pa kg mol^-1

Question 7

Which of the following statements is true for an ideal-dilute solution?

a) The solute and solvent both obey Raoult's law.

b) The solute obeys Raoult's law and the solvent obeys Henry's law.

c) The solute obeys Henry's law and the solvent obeys Raoult's law.

d) The solute and solvent both obey Henry's law.

Question 8

Calculate the minimum partial pressure of nitrogen that is necessary to achieve an aqueous ideal-dilute solution of concentration 1.00 mmol dm^-3. The Henry's law constant for nitrogen in water is 156 kPa m³ mol^-1.

a) 156 MPa

b) 156 kPa

c) 156 Pa

d) 156 mPa

Question 9

Calculate the change in the normal boiling temperature of an aqueous solution made by dissolving 15.0 g of bromobenzene, C₆H₅Br, in 250 cm³ of water. The ebullioscopic constant of water is 0.51 K kg mol^-1.

a) +0.31 K

b) +0.19 K

c) +7.75 K

d) +3.06 K

Question 10

Calculate the osmotic pressure exerted by an aqueous solution of sucrose, C₁₂H₂₂O₁₁, of mass concentration 6.51 g dm^-3 at 20°C. The osmotic virial coefficient for dilute aqueous solutions of sucrose at this temperature is 0.382 dm³ mol^-1.

a) 3.18 Pa

b) 3.18 kPa

c) 46.6 Pa

d) 46.6 kPa

Oxford University Press, Online Resource Centre, Chapter 06.

Chapter 06

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