Chm270 Final Exam

CONFIDENTIAL

AS/SEP 2011/CHM270

#t|
UNIVERSITI TEKNOLOGI MARA FINAL EXAMINATION

COURSE COURSE CODE EXAMINATION TIME

PHYSICAL CHEMISTRY CHM270 SEPTEMBER 2011 2 HOURS

INSTRUCTIONS TO CANDIDATES 1. This question paper consists of two (2) parts: PART A (10 Questions) PART B (5 Questions) 2. Answer ALL questions from all two (2) parts: i) Answer PART A in the Objective Answer Sheet. ii) Answer PART B in the Answer Booklet. Start each answer on a new page. Do not bring any materials into the examination room unless permission is given by the invigilator. Please check to make sure that this examination pack consists of: ) ) ) iv) the Question Paper a one - page Appendix an Answer Booklet - provided by the Faculty an Objective Answer
The half-life of this reaction is A. B. C. D. 3.8x1fJ- 1 s 92.4 s 120 s 6.9x10" 3 s

8.

Which of the following mixtures of liquid is expected to obey Raoult's Law? A. B. C. D. Ethanol and water Ethanol and propanone Benzene and ethylbenzene Hydrochloric acid and water

9.

What is the value of the degree of freedom, F at the triple point in the phase diagram of H 2 0? A. B. C. D. 0 1 2 3

10.

What is the name of the colloid if the dispersed phase is a solid and the dispersion medium is a liquid? A. B. C. D. Sol Aerosol Emulsion Foam

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CONFIDENTIAL

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4

AS/SEP 2011/CHM270

PARTB

QUESTION 1 a) i) Define an acid according to Lewis theory. (1 mark) ii) Write the ionization equation of ammonia in water and calculate the pH value of a 0.10 M ammonia solution. (Kb NH3 = 1.8 x 10"5) (2 marks) Calculate the pH of a 0.200 M solution of NH4CI. The Kb value of ammonia is 1.8x10- 5 andK w =1.0x10" 1 4 . (3 marks)

i)

b)

Consider the following reaction: H2(g) i) +
1

/202(g)

-> H20(l)

AH = -287 kJ mol"1

Is the reaction exothermic or endothermic? (1 mark)

ii)

What is the value of AH for the reaction : 2H20(I) -> 2H2(g)

+

02(g) (1 mark)
(R = 8.314 J K"1 mol"1) (3 marks)

QUESTION 3 a) The vapour pressure of water at 80°C is 0.467 atm. Determine the mass in grams of sucrose, C^H^On that must be dissolved in 180 g of water at 80°C to reduce the vapour pressure above the solution to 0.464 atm. (4 marks) The boiling point of hydrochloric acid and water are -85°C and 100°C respectively. The azeotropic mixture contains 20.2% hydrochloric acid and 79.8% water boils at 108.5°C. i) Sketch the boiling point versus composition curve for this mixture and label the axes, the boiling points and the curves. (4 marks) What type of deviation is produced by the mixture? (1 mark) iii) Identify the components that are distilled over if a mixture of 58% HCI and 42% water is subjected to fractional distillation. (2 marks)

b)

ii)

QUESTION 4 a) State two differences between a true solution and a colloid. (2 marks) b) Briefly explain the preparation of lyophobic sol using i) ii) Bredig's arc method. (2 marks) hydrolysis of iron(lll) chloride. (2 marks) c) Give two differences between physical and chemical adsorptions. (2