Saturday, September 26, 2009

JEE Chemistry Final Revision Set No. 11

1. 9.75 g of a substance when dissolved in 72.0 g of water, lowered its vapour pressure by 0.5 mm at a given temperature. The vapour pressure of water at this temperature is 25.0 mm. Calculate the molecular weight of solute.

2. Blood freezes at 272.44 K and a solution of 6.0 gm of Urea in 500 gm of water freezes at 272.63 K. Calculate osmotic pressure of blood at 310 K. (Assume density of blood at 310 K to be 1 g/cc).

3. Acetic acid in benzene forms a dimer. 1.65 gm of acetic acid when dissolved in 100 gm of benzene raised bte boiling point by 0.36°C. Calculate the Van't Hoff factor.
(kb for benzene = 2.57°C/m).

4. The heat of formation of ethane is -19.46 kcal. Bond energies of C-C, C-H and H-H are 80.0, 99.0 and 104.18kcal respectively. Calculate the heat of atomisation of graphite. (Answer: 171 kcal).

5. The standard molar enthalpies of formation of cyclohexane (liquid) and benzene(liquid) at 25°C are -156 and +49 kJ/mol respectivley. The standard enthalpy of hydrogenation of cyclohexane (liquid) at 25°C is -119 kJ/mol. Use these data to estimate the magnitude of the resonance energy of benzene. (Answer: -152 kJ/mol)

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