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Chem 221: Physical Chemistry Ii Question Paper

Chem 221: Physical Chemistry Ii

Course:Bachelor Of Science & Bachelor Of Education (Science)

Institution: Chuka University question papers

Exam Year:2013

CHUKA

UNIVERSITY

UNIVERSITY EXAMINATIONS

SECOND YEAR EXAMINATION FOR THE AWARD OF DEGREE OF
BACHELOR OF SCIENCE & BACHELOR OF EDUCATION (SCIENCE)

CHEM 221: PHYSICAL CHEMISTRY II

STREAMS: B.Sc& B.ED (SCIENCE) TIME: 2 HOURS

DAY/DATE: MONDAY 12/8/2013 8.30 A.M. – 10.30 A.M.
INSTRUCTIONS:

Answer Question ONE and any other TWO questions.

USEFUL DATA:

NA = 6,02 x 1023, ?= 3.14, 0oC = 273o K
H = 1, O = 16, Ka2 carbonic acid = 6.0 x 10-11, R = 1.987 Cal k-1 mol-1,
R = 8.314 J k-1 mol-1
KSP for BaS04 is 1.5 x 10-9
Ln x = 2.303 log x

QUESTION ONE (30 MARKS)

(a) (i) Explain the significance of Vander Waals parameters. [3 marks]

(ii) The Vander Waals parameter b for a certain gas is 0.0329 litre mol-1. Calculate the diameter of the molecule in nm, assuming that molecules
are spherical. [2 marks]

(b) (i) Explain why aqueous solution of sodium carbonate is alkaline.
[1 mark]

(ii) Derive an expression for the pH and hydrolysis constant of the above solution {1 b(i)}. [3 marks]

(iii) Calculate the pH of 0.001 M solution of sodium carbonate
{Ka2 = 6.0 x 10-11). [1 mark]
(c) (i) For one component system, the triple point is an invariant point. Discuss.
[4 marks]

(ii) Partial pressures, P, of bromine vapour observed at different mole fractions, x, of bromine in carbon tetrachloride solutions at 25oC are given in the table below.

P(mmHg) 1.52 2.39 4.27 5.43 9.57 10.27
X x 10-2 0.39 0.60 1.02 1.30 2.39 2.50

Confirm that, these figures conform to Henry’s law. [4 m
(iii) A mixture of water and an organic liquid A, immiscible in water, distils at 95oC when the external pressure is one atmosphere. The vapour pressure of water at 95oC is 635 mmHg.

Calculate the molecular weight of A if the distillate contains 40% by weight of water. [1 mark]

Calculate the weight of the water required for the steam distillation
of500g of A if its molecular weight be 160 awu. [1 mark]

(d) (i) Explain how the depression of freezing point of a solvent may be used to
determine the molecular weight of the dissolved substance. [4 marks]

(ii) For a solution of 0.911gm of carbon tetrachloride dissolved in 50.00gm of benzene the freezing point depression was found to be 0.603oC. Calculate the molecular weight of the carbon tetrachloride Kf is given as 5.12. [1 mark]

(iii) Briefly explain the following:

Alum is used in town water supply. [3 marks]

The sky looks blue. [2 marks]

QUESTION TWO (20 MARKS)

(a) (i) Discuss the applications of solubility product in the separation of copper,
zinc and magnesium from the mixture of their salts. [6 marks]

(ii) 100ml of 0.004M Ba(NO3)2 solution is mixed with 400ml of 0.05M Na2SO4. Will a precipitate of BaSO4 form? {KsP for BaSO4 is 1.5 x 10-9}
[3 marks]

(i) Write down the expression for the Maxwell’s distribution of molecular
speed and discuss it’s characteristics. [5 marks]

(ii) What is the temperature at which an oxygen molecule have the same RMS speed as a hydrogen molecule at 27oC? [1 mark]

How did Arrhenius account for the change in molar conductivity of an
electrolyte with dilution, and how have his ideas had to be modified?
[5 marks]

QUESTION THREE (20 MARKS)

(a) (i) Draw a well labelled phase diagram of KI – water system and discuss its
salient features. [7 ½ marks]

(ii) Discuss the variation of mutual solubility of nicotine and water with temperature. [2 marks]

(iii) A mixture of quinoline and water boils at 98.9oC under a pressure of 740mmHg. The distillate contains 7.79 x 10-2 kg of quinoline and 1kg
of water. The vapour pressure of quinoline at 98.9oC is 7.96 mmHg. Calculate the molar mass of quinoline. [2 marks]

(b) (i) A 2% solution (by weight) of a substance of unknown molecular weight in
toluene as a solvent has a vapour pressure of 752.4 mmHg at 110oC and a normal boiling point of 110.25oC. The normal boiling point of toluene is 110.00oC and the solute is non-volatile. Calculate the molecular weight of the solute and the heat of vaporization (per gram) of toluene (C6H5CH3)
(R = 1.987 Cal k-1mol-1). [5 marks]

(ii) A polymer mixture contains two polymers, one having molecular weight 100,000 and the other having molecular weight 60,000. The two components are present in equimolar concentration. Calculate the number average and the weight average molecular weights. [3 ½ marks]

QUESTION FOUR (20 MARKS)

(a) Briefly explain the following statement: “Origin of charge on colloidal particles”.
[8 marks]

(b) Derive a relationship between the elevation in boiling point of a solution and the molality of the solute from thermodynamic consideration. [7 ½ marks]

In a Cottrell determination, 22g of benzene was used as solvent. The readings on the differential thermometer before and after adding 0.586g of naphthalene (mol mass = 128), were 1.262 and 1.799 respectively. In a separate experiment, using the same amount of benzene but this time adding 0.627g of an organic compound X, the temperature readings were 1.269 and 1.963. Calculate the molecular mass of X. [4 ½ marks]

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Chem 221: Physical Chemistry Ii Question Paper

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