2012 c1 promo paper 2 questions

This question booklet consists of 11 printed pages.

HWA CHONG INSTITUTION

C1 Promotional Examination

Higher 2

CANDIDATE NAME

CT GROUP 12S

CHEMISTRY Paper 2 Structured Questions

Candidates answer on the Question Paper.

Additional Materials: Data Booklet.

9647/021 October 2012

1 h 10 min

INSTRUCTIONS TO CANDIDATES

1) Write your name and CT class clearly in the spaces at the top of this page.

2) Answer all questions in the spaces provided in this Question Booklet.

INFORMATION FOR CANDIDATES

The number of marks is given in brackets [ ] at the end of each question or part question.

You may use a calculator.

You are reminded of the need for good English and clear presentation in your answers.

FOR EXAMINERS’ USE ONLY

Paper 1 Paper 2 Paper 3 TOTAL

Multiple Choice Structured Free Response

Q1 / 10 Q1 / 20

Q2 / 15 Q2 / 20

Q3 / 9 Q3 / 20

Q4 / 11

/ 25 Subtotal / 45 Subtotal / 40

110

2

2012 HCI C1 H2 Chemistry Promotional Examination / Paper 2

Answer all the questions in the spaces provided. 1 The hydroxides of Group I metals (LiOH, NaOH, KOH, RbOH, CsOH) are highly corrosive

white solids which rapidly absorb water vapour on exposure to the atmosphere. All of these solids dissolve exothermically in water. The enthalpy change of solution, Hsol, is the energy change associated with the following reaction. M represents the Group I metal. MOH (s) M+ (aq) + OH⎯ (aq) The following diagram represents theoretical stages in the formation of aqueous MOH.

(a) (i) Express the enthalpy change of solution, Hsol , in terms of lattice energy and the enthalpy change of hydration, Hhyd.

………………………………………………………………………………………………

(ii) Explain whether the lattice energy of Group I metal hydroxide becomes more or

less exothermic down the group.

……………………………………………………………………………………………… ………………………………………………………………………………………………

(iii) Explain whether the enthalpy change of hydration of the ions, Hhyd, becomes

more or less exothermic down the group.

……………………………………………………………………………………………… ………………………………………………………………………………………………

3


(iv) When comparing Group I metal hydroxides, changes in Hhyd are more significant

than changes in lattice energy. Sketch your prediction in the trend of Hsol from LiOH to CsOH in the following graph.

[4] (b) A student wants to conduct a simple experiment to determine the trend of the Hsol of

the Group I metal hydroxides by dissolving a small sample of solid hydroxide in water and measuring the temperature change.

(i) State the following variables for this experiment: independent variable……………………………………………………………………. dependent variable……………………………………………………………………… controlled variable……………………………………………………………………….

(ii) Draw a labelled diagram to show the setup of apparatus in this experiment.

4


(iii) In the student’s experiment, he dissolves x g of solid KOH completely in y cm3 of

water and measures a temperature change of ∆T oC. Outline how you would use his results to determine the Hsol of KOH. Given that 4.3 J of energy is required to raise the temperature of 1.0 cm3 of a dilute aqueous solution by 1 oC.

[5] (c) From the information given on Group I metal hydroxides, identify one possible source

of error in the experiment, apart from heat lost to the surroundings, and discuss its impact on the value of the ∆Hsol calculated.

…………………………………………………………………………………………………….. ……………………………………………………………………………………………………..

[1]

[Total: 10]

5


2 Propene and hydrogen chloride react together according to the equation:

CH2=CHCH3 (g) + HCl (g) CH3CHClCH3 (g) ∆H < 0

(a) To study the kinetics of this reaction, two students carried out their own different sets of

experiments and obtained the following graphs.

(i) Use Student A's graph to deduce the order of reaction with respect to propene.

……………………………………………………………………………………………… ………………………………………………………………………………………………

(ii) Explain why the half-life of propene in Student B's graph is not constant.

……………………………………………………………………………………………… ……………………………………………………………………………………………… ………………………………………………………………………………………………

(iii) Given that the reaction is first order with respect to HCl, write the rate equation

for the reaction, in terms of partial pressures.

(iv) Determine the value of the rate constant, k, for the reaction.

0 0

6


(v) Deduce the half-life of propene when the partial pressure of HCl is halved in

Student A’s experiment.

[5] (b) Describe the mechanism for the reaction between propene and HCl to produce

CH3CHClCH3.

[3]

(c) Using relevant bond energy data from the Data Booklet, draw an energy cycle to determine the enthalpy change of the reaction between propene and HCl.

[3]

7


(d) Hence, sketch the energy profile diagram of the reaction between propene and HCl.

Label the activation energy and enthalpy change of the reaction.

[2]

(e) Explain whether the product formed in this reaction is optically active.

…………………………………………………………………………………………………….. ……………………………………………………………………………………………………..

[1]

(f) Explain why there is virtually no 1-chloropropane produced in the reaction of propene with HCl.

…………………………………………………………………………………………………….. ……………………………………………………………………………………………………..

[1]

[Total: 15]

8


3 At high temperatures within the cylinders of a car engine, N2 and O2 can form NO, which

combines with more O2 to form NO2, a toxic pollutant that contributes to photochemical smog. This process takes place according to the following steps:

(1) N2(g) + O2(g) 2NO(g) Kc1 = 0.013 (2) 2NO(g) + O2(g) 2NO2(g) Kc2 = 7.0 × 105 (a) (i) Write the balanced equation for the overall reversible reaction, including state

symbols. ………………………………………………………………………………………………

(ii) Write the expression for the equilibrium constant for the overall reaction, Kc(overall), including the units.

(iii) Show that the expression for Kc(overall) is the product of the expressions of the equilibrium constants Kc1 and Kc2.

(iv) In a study, an engineer mixed some N2 and O2 in a 5.0 dm3 vessel at 3000 K. At equilibrium, O2 and NO2 were found to be present in a mole ratio of 1:10. Using your answer to (a)(iii) or otherwise, determine the amount in moles of N2

present at equilibrium.

(v) To increase the amount of NO2 obtained, the engineer doubled the amount of N2

and O2 added to the vessel. State and explain how this change will affect the value of Kc(overall).

……………………………………………………………………………………………… ………………………………………………………………………………………………

[7]

9


(b) Orange street-lamps contain sodium with a small amount of neon. Light is produced

when the gaseous atoms are ionised in an electric field.

Ne (g) Ne+ (g) + e 1st I.E. = +2080 kJ mol–1 Na (g) Na+ (g) + e 1st I.E. = +494 kJ mol–1 (i) Explain the difference in the first ionisation energies of neon and sodium.

……………………………………………………………………………………………… ………………………………………………………………………………………………

(ii) When the lamps are switched on, they first emit a red glow characteristic of neon, but after some time, the orange glow of sodium predominates. Suggest why neon is ionised first even though its first ionisation energy is much higher than that of sodium.

……………………………………………………………………………………………… ………………………………………………………………………………………………

[2]

[Total: 9]

10


4 The benzene ring usually resists chemical oxidation but the process may be accomplished

microbiologically. The bacterium Pseudomonas putida in the presence of air rapidly converts benzene into compound R.

(a) Using the [O] notation for the oxidation of organic compounds, write a balanced equation for this oxidation.

[1]

(b) Is compound R optically active? Explain why. …………………………………………………………………………………………………….. ……………………………………………………………………………………………………..

[1]

(c) In the structure of compound R, the two –OH groups are on the same side of the plane of the ring, i.e. the –OH groups are in a cis arrangement. Compound S is a trans isomer of compound R. Draw the structure of compound S, showing clearly the trans arrangement.

[1]

R

11


(d) Compound R is a starting material in the reaction scheme below.

(i) State the type of reaction that occurs in Step I. ………………………………………………………………………………………………

(ii) State the reagents and conditions in Step II. ………………………………………………………………………………………………

(iii) In the boxes provided above, draw the structures of all carbon-containing products formed in Steps III and IV.

(iv) Draw one other dichlorocyclohexane that is a structural isomer of compound U and which does not contain any chiral carbon.

(v) Describe one simple chemical test to distinguish between compounds T and U. You should state the reagents, conditions and the expected observations with each compound.

……………………………………………………………………………………………… ……………………………………………………………………………………………… ………………………………………………………………………………………………

[8]

[Total: 11]End of Paper

R T U

2012 c1 promo paper 2 questions

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