CHM095 II 2006

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CONFIDENTIAL AS/OCT 2006/CHM095

UNIVERSITI TEKNOLOGI MARAFINAL EXAMINATION

COURSECOURSE CODEEXAMINATIONTIME

CHEMISTRY IICHM095OCTOBER 20063 HOURS

INSTRUCTIONS TO CANDIDATES1. This question paper consists of five (5) questions.2. Answer ALL questions in the Answer Booklet. Start each answer on a new page.3. Do not bring any material into the examination room unless permission is given by theinvigilator.4. Please check to make sure that this examination pack consists of:

i) the Question Paperii) anAnswer Booklet - provided by the Faculty

DO NOT TURN THIS PAGE UNTIL YOU ARE TOLD TO DO SOThis examination paper consists of 6 printed pages

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CONFIDENTIAL 2 AS/OCT 2006/CHM095

QUESTION 1a) Define the following terms:

i) weak acidii) percent ionisationiii) hydrolysis of saltiv) an acidic buffer (6 marks)b) Identify the acid-base conjugate pairs in the following reactions:

i) CH3CH2NH2 + H2O *CH3CH2NH3+ + OKii) HCO3- + HCO3- *. H2CO3 + CO 32" (2 marks)c) Predict the pH (>7, < 7, or 7) of aqueous solutions containing the following salts:

i) KBrii) AI(NO3)3iii) BaCI2iv) Bi(N03)3 (2 marks)d) Given K b for ammonia at 298 K is 1.75 x 10"5 mol dm"3, calculate

i) the percent ionisation of ammonia solutionii) the pH of the buffer system made up of 0.15 M NH3/0.35 M NH4CI. (8 marks)e) The K a of a certain indicator is 2.0 X10"6. The colour of Hln is green and that of In" isred. A few drops of the indicator are added to a HCI solution, which is then titratedagainst a NaOH solution. At what pH will the indicator change colour? (2 marks)

QUESTION 2a) i) List any four (4) factors that can affect the rate of reaction.ii) Why does an increase in temperature result in an increase in reaction rate?iii) Comm ent on the effect of a catalyst on enthalpy of reaction (5 marks)

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b) Sulphuryl chloride, SO 2CI2 decomposes when heated.SOC2(g) -SO(g +C2(g

In an experiment, the initial concentration of sulphuryl chloride was 0.0248 mol L"1. Ifthe rate constant is 2.2 x 10~ 5 s"1, what is the concentration of SO2CI2 after 4.5hours?. The reaction is first order. (3 marks)c) Nitrogen gas reacts with hydrogen gas to form ammonia gas according to thepotential energy diagram below:

Potential energy (kJ)

N2(fl> 3H 2(9)

91.8kJ

2NH3(g)

Reaction Coordinatei) State with reason whether the reaction is endothermic or exothermic.ii) If the activation energy for the forward reaction is 5.0 kJ, calculate theactivation energy for the reverse reaction,iii) Write the chemical equation for the reverse equation, including the energyterm as well,iv) Predict the value of the activation energy of the reaction in the diagram, if a

catalyst is added. (4 marks)


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d)

e)

Nitric ox ide, NO reacts with hydrogen to give nitrous oxide, N2O and water.2NO(g) +H2(g) -> N20(g) + H20(g)

In a series of experiments, the following initial rates of disappearance of NO wereobtained:ExperimentNo.

123

[NO],mol dm6.4 xirj31 2 . 8 x1 Q -36 .4 x10 "3

[HJ,mol dm2.2 X10"32.2 X10"34.5X10-3

Rate of reaction,mol dm"3 s"12.6 x10'51.0x10'45.1 x10'5

i) What is the overall order?ii) Calculate the rate constant with correct unit for the reaction.iii) Write the rate law for the reaction. (6 marks)Nitric oxide, NO is believed to react with chlorine according to the followingmechanism:

NO + CI2 - NOCI2NOCI2 +NO - 2NOCI (elementary reaction)(elementary reaction)State the molecularity of each elementary reaction.Identify any intermediate species in the reaction.What is the overall equation? (2 marks)

QUESTION 3a)

b)

i) State Mess's Law.ii) What is the difference between specific heat and heat capacity? (5 marks)A chemical engineer studying the properties of fuels placed 1.500 g of a hydrocarbonin the bomb of a calorimeter and filled it with oxygen gas. The bomb was immersedin 2500 cm3 of water and the reaction initiated. The water temperature rose from20 .00C to 23.55C. If the calorimeter (excluding the water) had a heat capacity of403 J C ~ 1 , calculate the heat of combustion of the fuel in kJ g"1. (Assume that thedensity of water is 1g cm"3 and the specific heat of water is 4.18 J g"1 C"1). (4 marks)


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c) Predict with reasons, the value of AH(greater than, less than, or equal to zero) forthese elements at 25C:

(4 m arks)d) Consider the following thermochem ical data:

equation 1equation 2equation 3

H2(g) ~Br2(g) -2H(g)2Br(g)!r2(g) - 2HBr(g)

AH = 436.4 kJ mol'1AH = 192.5kJmor1AH = -72.4 kJ mol'1

Calculate AHfor the reactionH(g) + Br(g) ~ * HBr(g) (5 marks)

QUESTION 4a) The standard electrode potential for zinc and copper are -0.76 V and +0.34Vrespectively. Explain this statement w ith regards to the electrochemical series.(3 marks)b) i) From the following E

evalues below:

S2082-(i) + 2e t; 2SO 42-(aq) E*=+2.01V2H2O(|) + O2(g) +4e t; 4OH-(aq) E*=+0.40VWrite a balanced equation for a spontaneous reaction.

ii) Determine the oxidation number for sulphur in S2O82" and SO42". (6 marks)c) i) Calculate the e.m.f. of the following cell:

Zn (8) / Zn2+(0.8 mol drrT3) // Cu2+(0.4 mol dm'3) / Cu(s) (6 marks)What is the effect on the e.m.f. of the cell above if the concentration of theCu2+ ions is increased? Explain your answer.

(3 marks)

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QUESTION 5a) Consider the molecule shown: H3C-CH=CH2

i) What are the hybrid orbitals of each carbon atom in the molecule? Justifyyour answer.ii) Name the molecule above.iii) How many sigma bonds and pi bonds are there in the molecule? (6 marks)b) Discuss how you can classify the following compounds to be alkanes, cycloalkanes,alkenes, or alkynes, without drawing their formulas:

ii) C4H6iii) C6H12iv) C7H14 (6 marks)c) i) Suggest two chemical tests that can be used to distinguish between thesetwo compounds:

and CH3CH2CH2CH=CH2ii) Complete the following equation and identify the products:

HCOOH + CH3OH - products (4 marks)d) Write structural formulas for the following compounds:

i) frans-2-penteneii) 4-ethyl-trans-2-heptene (2 marks)e) A compound has the empirical formula C5H12O. Upon controlled oxidation, it isconverted into a compound of empirical formula CsH^O, which behaves as a ketone.

Draw possible structures for the original compound and the final compound. (6 marks)

END OF QUESTION PAPER

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CHM095 II 2006