AS/SEP 2011/CHM270
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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 …show more content…
Sheet - provided by the Faculty
3.
4.
DO NOT TURN THIS PAGE UNTIL YOU ARE TOLD TO DO SO
This examination paper consists of 7 printed pages
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PART A Identify the conjugate base of HP042" in the following reaction. HC03" A. B. C. D. H20 HCCV H 2 C0 3 PO43+ HPO42" = 5 ^ H2CO3 + P0 4 3 '
1.
2.
A 0.10 M HF solution is 8.4% ionized. Calculate the H+ ion concentration. A. B. C. D. 8.4x10" 3 M 8.4x10" 2 /W 0.84 M 0.10 M
3.
Calculate the pH of a buffer solution which contains 0.25 M benzoic acid, C6H5C02H and 0.15 M sodium benzoate, C6H5C02Na. Given Ka = 6.5 x 10"5. A. B. C. D. 4.83 4.19 3.97 3.40
4.
Which one of the following species has the highest entropy, S° at 25°C? A. B. C. D. CH3OH(l) CO(g) MgC03(s) H20(l)
5.
Which of the following equations represent a reaction that gives the heat of formation of H2S04(l)? A. B. C. D. 2H(g) + S(g) + 40(g) - * H2S04(l) H2(g) + S(g) + 202(g) -> H2S04(l) H2S04(l) -> 2H(g) + S(s) + 40(g) H2(g) + S(s) + 202(g) ^ H2S04(l)
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AS/SEP 2011/CHM270
6.
The following factors affect the rate of a chemical reaction except A. B. C. D. the concentration of the reactant. the temperature of the experiment. the volume of the reactions. the size of the particles of solid used as the reactant.
7.
A first reaction has a rate constant of 7.5 x 10"3 s"1.
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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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) …show more content…
c)
Calculate AH for the reaction below: C2H4(g) + H2(g) -> C2H6(g)
Given the following reactions and their respective enthalpy changes: III. III. C2H6(g) + 31/202(g) -> 2C02(g) + 3H20(I) C2H4(g) + 302(g) -> 2C02(g) + 2H20(I) 2H2(g) + 0 2 (g) -> 2H20(g) AH=-1560kJ AH = -1411kJ AH = -572kJ (3 marks)
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QUESTION 2 a) Carbon monoxide burns to form carbon dioxide according to the reaction below. 2CO(g) + 0 2 (g) -> 2C02(g)
Information on the reaction is given in the following table.
[CO] (mol L1) 0.02 0.04 0.02
[0 2 ] (mol L1) 0.02 0.02 0.04
Initial Rate (mol L"1 min'1) 3.68 x 10* 1.47x10^ 7.36 x 1 0 s
i)
Determine the order of reaction for each reactant. (3 marks)
ii)
Write the rate equation for the reaction. (1 mark)
iii)
Calculate the rate constant for the reaction and give its unit. (2 marks)
b)
Ozone, 0 3 , in the earth's upper atmosphere decomposes according to the equation 20 3 (g) 302(g)
The mechanism of the reaction is thought to be as follows: Step 1 : Fast, reversible 03(g) Step 2 : Slow -»*" 0 2 (g) 202(g) (1 mark) i) Which of the steps is rate-determining? (1 mark) ii) Write the rate equation for the rate-determining step.
03(g) + O(g) ^ ^
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c)
Calculate the activation energy, Ea, for the reaction N205(g) 2N02(g) +
1
/202(g)
from the observed rate constant: k at 25°C = 3.46x10" 5 s" 1 and k at 55°C = 1.5 x 10"3 s 1 .
(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
marks)
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d)
A sample of 4.5 g ethane, C2H6 occupies 12.7 L at 310 K. Calculate the work done (in Joules) when the gas expands isothermally against a constant external pressure of 2.67 x 104 Pa until its volume has increased by 3.3 L. (3 marks)
QUESTION 5 A voltaic cell is constructed by immersing a lead plate into Pb(N03)2 solution at one half-cell and a silver plate into a AgN0 3 solution at another half-cell. a) The standard electrode potentials for lead and silver are given below. Pb2+(aq) + 2e — Pb(s) Ag+(aq) + e -» Ag(s) £° = -0.13 V E° = +0.80 V
i)
Which element is the stronger reducing agent? (1 mark)
ii)
Write the chemical equations for the reaction at the anode, cathode and the overall reaction that occur in the electrochemical cell above. (2 marks) Determine the standard e.m.f. for the above electrochemical cell. (2 marks)
iii)
iv)
Determine the e.m.f. of the cell if the concentration of lead nitrate and silver nitrate at 25°C are 0.60 M and 0.20 M respectively. (R = 8.314 J K"1 mol"1, Faraday's constant = 96500 C mol'1) (3 marks)
b)
Electrolysis of water using platinum electrode produces oxygen gas at the anode and hydrogen gas at the cathode according to the following half-reactions. Anode: 2H 2 0 -> 0 2 + 4H+ + 4e Cathode: 4H 2 0 + 4e -» 2H2 + 40H" How many grams of hydrogen gas are liberated after 5.0 minutes with a current of 0.2 A? (1 Faraday = 96500 C; molar mass of hydrogen atom = 1 g mol"1) (3 marks)
END OF QUESTION PAPER
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APPENDIX 1
AS/SEP 2011/CMM270
TABLE OF ATOMIC MASSES
Element Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Titanium Vanadium Chromium Manganese Iron Cobalt Copper Zinc Arsenic Selenium Bromine Rubidium Silver Cadmium Tin Antimony Iodine Cesium Barium Platinum Mercury Lead Symbol H He Li Be B C N 0 F Ne Na Mg Al Si P S CI Ar K Ca Ti V Cr Mn Fe Co Cu Zn As Se Br Rb Ag Cd Sn Sb I Cs Ba Pt Hg Pb Atomic Mass 1.0 4.0 7.0 9.0 11.0 12.0 14.0 16.0 19.0 20.0 23.0 24.0 27.0 28.0 31.0 32.0 35.5 40.0 39.0 40.0 48.0 51.0 52.0 55.0 56.0 59.0 64.0 65.0 75.0 79.0 79.9 85.5 108.0 112.4 118.7 122.0 127.0 133.0 137.3 195.0 200.0 207.0
Avogadro's number, NA = 6.02 x 1023 mol"1 One mole of any gas at STP = 22.4 dm3 or 22.4 L
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