SOUTH EASTERN KENYA UNIVERSITY UNIVERSITY EXAMINATIONS 2014/2015 CHE 102: PHYSICAL CHEMISTRY I TIME: 1:30-3:30PM DATE: 22/4/15

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1 SOUTH EASTERN KENYA UNIVERSITY UNIVERSITY EXAMINATIONS 2014/2015 FIRST YEAR THIRD SEMESTER EXAMINATION FOR THE DEGREE BACHELOR OF SCIENCE BIOCHEMISTRY AND MOLECULAR BIOLOGY CHE 102: PHYSICAL CHEMISTRY I TIME: 1:30-3:30PM DATE: 22/4/15 INSTRUCTIONS TO CANDIDATES (a) Answer question One and any other Two questions (b) Question 1 carries 30 marks while the other questions carry 20 marks each (c) Illustrate your answers with well labeled diagrams where appropriate

2 Question 1 (30 marks) (a) State the following gas laws and also give their corresponding mathematical forms. In each case and also in the form of an equation, indicate the conditions under which the law is applicable giving the units for each quantity in the equation:- (i) Boyle s law (2 mark) (ii) Charles law (2 mark) (iii) Avogadro s law (2 mark) (iv Define absolute zero and absolute zero scale. Write the relationship between o C and K (b)(i) State Raoult s law of volatile solutions. (ii) Show that for a binary solution. (4 marks) (c) (i) Define what are the colligative properties of a solution containing a nonvolatile solute and state them. (ii) Use a phase diagram to illustrate the colligative properties. (iii) What are the boiling point and freezing point of a 2.47 m solution of naphthalene in benzene? (The boiling point and freezing point of benzene are 80.1 o C and 5.5 o C respectively). (K f of benzene = 5.12 o C/m, K b = 2.53 o C/m) (d) (i) Define Bronsted acids and bases and give an example of a conjugate pair in an acid-base reaction. (ii) Write the formulas of the conjugate bases of the following acid. (i) HNO 2 (ii) H 2 S 1

3 Question 2 (20 marks) (a) (i). State the basic assumptions of the kinetic molecular theory of gases. (ii) Using the kinetic theory of gases, derive the ideal gas equation PV = nrt. (5marks) (b)(i) Benzene and toluene form nearly ideal solutions. If at 300 K, and, compute the vapour pressure of a solution containing 0.60 mole fraction toluene and also calculate the mole fraction of toluene in the vapour for this composition of liquid. (ii) Use a phase diagram to illustrate total and partial vapour pressure curves for an ideal solution over the whole concentration range at constant temperature. Question 3 (20 marks) (a) Consider the reaction at equilibrium: C (s) + CO 2(g) = 2CO (g) Has equilibrium constant K p of 1.5 at T = 700 o C. (i) Write the equilibrium constant expression in terms of partial pressures of the reactants and products. (ii) Calculate the equilibrium pressures of the species if the equilibrium pressure of the system is found to be 5.00 atm. (b) For the reaction: C (g) + D (g) = 2E (g), write the equilibrium constant expression. (c) Predict the direction of the reaction if the following is done to the mixture:- (i) Temperature is increased (ii) Pressure is increased (iii) A catalyst is added. Give a reason to support your answer. 2

4 (d) If 2 moles of C and D each kept in a one litre flask and allowed to attain equilibrium, what would be the equilibrium composition of C, D, and E if K c = 100. (e) (i) How many grams of oxygen are there in a 50.0L tank at 21 o C when the oxygen pressure is 15.0 atm ( 2 marks) (ii) Nitrogen is heated to 500 K in a vessel of constant volume. If it enters at a pressure of 100 atm and a temperature of 300 K, what pressure would it exert at the working temperature if it behaved as a perfect gas Question 4 (20 marks) (a) (i)calculate the concentration of OH - ions in a M HCl solution. (ii) Predict the direction that predominates in this reaction: (1 mark) F - (aq) + H 2 O (l) = HF (aq) + OH - (aq) (iii) The K a for benzoic acid is Calculate the ph of a 0.10 M benzoic acid solution. (iv) The ph of a 0.30 M solution of a weak base is What is the K b of the base? (v) Carbonic acid is a diprotic acid. Explain what that means. (1 mark) (b) Given that 3.50 moles of NH 3 occupy 5.20 L at 47 o C, calculate the pressure of the gas (in atm) using (i) the ideal gas law and (ii) the van der Waals equation, and state which of the two is closer to experimental value. (4 marks) (R = L.atm/K.mol, For NH 3, a = 4.17 atm.l 2 /Mol 2, b = L/Mol) (c) State Dalton s law of partial pressures, and show that the total pressure of a gaseous system is given by (d) Calculate the root-mean-square speed of helium atom in m/s at 25 o C. 3

5 R = J/K, Mass of H e = g /mol (e). Oxygen gas generated in the decomposition of potassium chlorate and collected over water at 20 o C. The volume of the gas collected at atmospheric pressure of 755 Torr is 370mL. Calculate the mass (in grams) of oxygen gas obtained. The pressure of the water vapour at 20 o C is 17.5 Torr. Question 5 (20 marks) (a) (i) The van der Waals equation for real gases is as shown below: Explain the corrective terms for P and V. (ii) Under what set of conditions would a gas be expected to behave most ideally? (b) state the Graham s law of diffusion and show its mathematical expression (c) A sample of 0.892g of potassium chloride (KCl) is dissolved in 54.5g of water. What is the percent by mass of KCl in this solution? (d) Describe an ideal solution. (e) When 18.04g of a sugar were dissolved in 100g of water, the vapour pressure of the later at 20 o C was lowered from 17,535 mmhg to mmhg. Calculate the molecular weight of the sugar. (f) A solution containing 4.0g of a polyvinyl chloride polymer in 1 litre of dioxane was found to have an osmotic pressure of 6.4 x 10-4 atm at 27 o C. Calculate the approximate molecular weight of the polymer. 4