Solutions, Colligative Properties, Phase Equilibria, and Adsorption — DU B.Sc (hons) Chemistry Previous Year Question Papers

Attempt SIX questions in all. a. b. c. How does the addition of succinic acid affect the C.S.T of phenol-water system? Explain. The slope of the sublimation curve in the phase diagram of water is greater than that of the vapourization curve. Explain. State the Nernst Distribution Law along with a suitable formula. d. e. f. g. Azeotropic mixtures have definite compositions and definite boiling points but they are not compounds. Explain. Write the expressions for Gibbs Phase Rule and Reduced Gibbs Phase Rule. Name the various terms used. Chemisorption results in decrease in entropy of the gas, still it is a spontaneous process. Why? Explain in terms of ΔG, ΔH and ΔS? What do you mean by the triple point of water? 2. Write short notes on (any three) (5 x 3 = 15) a. Difference between physisorption and chemisorption. b. Steam distillation. c. van’t Hoff factor and abnormal molecular masses. 3. 4. 5. d. Phase diagram of phenol-water system. e. Langmuir Adsorption Isotherm. a. b. c. What are colligative properties? Explain osmosis and osmotic pressure with a suitable diagram. 1.50 g of a non-volatile organic substance was dissolved in 140 g of acetone at 20°C. The vapour pressure of the solution was found to be 181.5 torr. Calculate the molar mass of the substance, given that the vapour pressure of pure acetone at 20°C is 186 torr. Define “degree of freedom”. Find the number of components, number of phases and degrees of freedom for the following system a. Draw a well-labelled phase diagram of the Sulphur system and explain the different areas, curves and points. Also calculate the degrees of freedom corresponding to the areas, curves and points. b. Derive the following equation starting from the Duhem-Margules Equation. 𝑑𝜒 c. Derive the Gibbs phase rule for a non-reactive system at equilibrium containing C components and P phases. a. Using the phase diagrams, compare the slopes of the fusion curve of H2O and CO2 systems. Explain using Clausius-Clapeyron equation. b. State the Konowaloff Rule. On distillation of each of the following mixtures, find which component will be obtained in the residue and which one in the distillate. The vapour pressures of the components are given within brackets: (i) n-hexane (45.5 mm Hg) and n-heptane (11.4 mm Hg) (ii) benzene (51.3 kPa) and toluene (18.5 kPa) c. Metals X and Y exhibit a simple eutectic diagram. Following table gives the break and halt points for various mixtures of X and Y. Draw the phase diagram and find the eutectic composition and temperature. Mass percent of Y 0 20 40 50 70 85 100 Break Temperature/ °C 800 600 400 - 415 500 600 Halt Temperature/ °C 350 350 350 350 350 350 350 6. a. State and derive the lever rule for a 2-component system. b. c. To 100 mL of an aqueous solution containing 0.3 g of aspirin, 50 mL of ether were added. The mixture was shaken and allowed to equilibrate at 293 K. The distribution coefficient of aspirin between ether and water is 5.9.