2011 Trial Exam P2 Quest

SEKOLAH MENENGAH KEBANGSAAN SEAFIELD, SUBANG JAYA

Upper Six Time: 2 ½ hoursTrial Examination

2011

CHEMISTRY – Paper 2

Instructions to candidates:

Answer all the questions in Section A. Write your answers in the spaces provided.

Answer any four questions from Section B. For this section, write your answers on the answer sheets provided. Begin each answer on a fresh sheet of paper and arrange your answers in numerical order. Tie your answer sheets to this booklet.

All working should be shown. For numerical answers, units should be quoted wherever they are appropriate

Answers may be written in either English or Bahasa Malaysia.

A Data Booklet is provided.

For examiner’s use

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Total

Circle the questions you have answered in this table.

Prepared by:

………………………..(Pn. Looi Chui Yean)

Checked by:

…………………………(Pn. Poh Bee Lee)

Verified by:

……………………..(Pn. Suhaili Elias)

Section A [40 marks]Answer all the questions in this section.

1. (a) Sodium-24 isotope is used in medicine to study the blood circulatory system.

(i) Write the electronic configuration of sodium-24 isotope. [1 mark]

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(ii) How many orbitals of sodium-24 isotope are fully filled? [1 mark]

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(iii) State the orbitals of sodium-24 ion which contain valence electrons. [1 mark]

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(iv) State one reason why sodium-24 isotope is rarely found in its natural state. [1 mark]

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(b) Teryllium is an element from Group 16 in the Periodic Table.

(i) Draw the Lewis structure of teryllium tetrachloride. [1 mark]

(ii) What is the shape of a teryllium tetrachloride molecule? [1 mark]

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(iii) Is teryllium tetrachloride a polar or non-polar molecule? [1 mark]

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(c) Cyanide ion, CN-, can act as a monodentate ligand. The carbon atom undergoes sp

hybridisation. Draw an orbital overlap diagram to show the cyanide ion. [3 marks]

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2. (a) Aluminum is extracted by electrolysis of purified aluminium oxide found in the mineral, bauxite.

(i) Why does the extraction of aluminium from purified aluminium oxide require a high temperature? [1 mark]

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(ii) Cryolite is used to lower the melting point of aluminium oxide during the extraction of aluminium. Write the chemical formula of cryolite. [1 mark]

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(iii) At which electrode is aluminium produced during the extraction? Write the half-equation to show the reaction at this electrode. [1 mark]

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(b) Aluminium fluoride and aluminium chloride each sublime when heated. The former has a sublimation point of 1270 oC whereas the latter has a sublimation point of 178 oC .

(i) What do these two figures suggest about the nature of the bonding in these two compounds? [1 mark]

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(ii) Suggest reasons for any differences in their bonding. [2 marks]

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(iii) Draw a displayed formula to show the type of bonding in the molecules of aluminium chloride vapour formed. [1 mark]

(iv) Explain the reaction of aluminium chloride with water. [3 marks]

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3. (a) The thermal decomposition of phosphine (PH3) into phosphorus and molecular hydrogen is a first-order reaction:

4 PH3(g) → P4(g) + 6H2(g)

The half-life of the reaction is 35.0 s at 680ºC.

(i) Write the rate equation for the above reaction. [1 mark]

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(ii) Calculate the rate constant for the reaction [2 marks]

(iii) Calculate the time required for 95% of the phosphine to decompose. [2 marks]

(b) When steam is passed over white hot coke, a combustible mixture of hydrogen and carbon monoxide gases is produced according to the equation below:-

H2O(g) + C(s) H2(g) + CO(g) ∆H = +131 kJ mol-1

State and explain how the amount of carbon monoxide gas in the equilibrium mixture would change if there is

(i) a decrease in the pressure [2 marks]

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(ii) When steam was passed over coke at 730 oC, the following partial pressures were obtained at equilibrium: P(H2O) = 90.0 kPa ; P(H2) = 183 kPa. Calculate the equilibrium constant for the reaction at this temperature. [3 marks]

4. (a) Carboxylic acids are organic acids obtained from plants and animals. The structural formula of four carboxylic acids are given below.

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(i) Arrange the acids in the order of increasing acidity. [2 marks]

(ii) Which of the above acids has the stongest conjugate base?[1 mark]

(iii) How does the –NO2 group affect the acidity of [2 marks]

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(b) can be used to make polymers

(i) State the type of polymerisation involving this acid. [1 mark]

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(ii) Draw the structure of the polymer. [1 mark]

(iii) What is the functional group present in the polymer? [1 mark]

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(c) CH3COOH can be used to prepare a buffer solution.(i) State one chemical that needs to be added to CH3COOH to produce a buffer

solution.

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(ii) Give the structural formulae of the species that are responsible for the buffer action of the solution. [2 marks]

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CH3COOH, – COOH, – COOHO2N- – COOH HO-

– COOH. HO-

– COOH. HO-

Section B [ 60 marks]

Answer any four questions in this section.

5. (a) The boiling point-composition curves for the mixture of ethanol and water at constant pressure is shown in the graph below.

(i) Sketch and label the vapour-composition curve for the mixture of ethanol and water. [3 marks]

(ii) Explain the type of deviation from Raoult's law exhibited by the mixture of ethanol and water. [4 marks]

(iii) What is meant by azeotrope? [2 marks]

(iv) From the above graph, determine the vapour composition of the distillates when 45.0% ethanol solution is fractionally distilled . State the temperatures at which these distillates are obtained. [2 marks]

(b) A diaphragm cell used in the commercial electrolytic production of chlorine and sodium hydroxide is shown below.

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(i) The ionic equation for the reaction at the anode is

2Cl- → Cl2 + 2e

Write an ionic equation for the reaction at the cathode. [1 mark]

(ii) Why is the porous asbestos diaphragm used in this cell? [1 mark]

(iii) Name a chemical substance Q formed when chlorine and sodium hydroxide react, and write a balanced equation for the reaction. [2 marks]

6. (a) Explain what is meant by the Bronsted-Lowry theory of acids and bases. [2 marks]

(b) The Ka values for some organic acids are listed below.

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acid Ka / mol dm-3

CH3COOH 1.7 x 10-5

ClCH2COOH 1.3 x 10-3

Cl2CHCOOH 5.0 x 10-2

(i) Explain the trend in Ka values in terms of the structures of these acids. [3 marks]

(ii) Calculate the pH of a 0.10 mol dm-3 solution of ClCH2COOH. [2 marks]

(iii) Use the following axes to sketch the titration curve you would obtain when 20 cm3 of 0.10 mol dm-3 NaOH is added gradually to 10 cm3 of 0.10 mol dm-3 ClCH2COOH.

[3 marks]

(iv) Suggest a suitable indicator for this titration. [1 mark]

(c) (i) Write suitable equations to show how a mixture of ethanoic acid, CH3COOH, and sodium ethanoate acts as a buffer solution to control the pH when either an acid or an alkali is added. [2 marks]

(ii) Calculate the pH of a buffer solution containing 0.10 mol dm-3 ethanoic acid and 0.20 mol dm-3 sodium ethanoate. [2 marks]

7. By using the standard reduction potential values from the Data Booklet, predict whether the pair of reagents given below will react when mixed together.

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pH oNaO

Volume of NaOH added / cm3

(a) (i) FeCl3(aq) and KI(aq)

(ii) Ag(s) and Fe(NO3)3(aq)

Write a balanced ionic equation for the reaction you predict will happen. [6 marks]

(b) To replace the silver metal that has peeled off from a silver trophy, 0.60 g of silver metal need to be electroplated on it. Calculate the time required if a current of 0.25 A is allowed to flow through the electrolytic cell in order to accomplish this task.[Relative atomic mass Ag, 108; Faraday constant, 96500 C mol-1] [3 marks]

(c) (i) Draw a Born-Haber energy cycle for the formation of CaF2 from its elements.[4 marks]

(ii) Using the above energy cycle and together with the data given below, calculate the lattice energy of CaF2(s).

Enthalpy of atomisation of Ca = + 178 kJ mol-1

First ionization energy of Ca = + 590 kJ mol-1

Second ionization energy of Ca = + 1150 kJ mol-1

Enthalpy of atomisation of F = + 158 kJ mol-1

Electron affinity of F = - 328 kJ mol-1

Enthalpy of formation of CaF2 = - 1220 kJ mol-1

[2 marks]

8. (a) Nitrogen dioxide, NO2, is a brown gas that is a constituent of smogs caused by cars in cities.

(i) Suggest how NO2 is formed in a car engine and how it may be removed from exhaust gases. [2 marks]

(ii) At a temperature of 320 K and a pressure of 1.0 x 105 Pa (1.0 atm), 0.50 g of the gaseous NO2 / N2O4 mixture takes up a volume of 190 cm3.

Calculate the average Mr of the mixture. [3 marks]

(b) (i) Explain the term ionisation energy.[2 marks]

(ii) Sketch the graph of the second ionisation energy against proton number for Period 3 elements from sodium to argon. Explain the trend of the graph. [5 marks]

(iii) The Period 3 elements also show a periodic change in other physical properties. Explain the variation of the atomic radii of the elements across the period. [3 marks]

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9. A hydrocarbon with the empirical formula of C7H6 has a relative molecular mass of 180.

(a) Determine the molecular formula of the hydrocarbon. [2 marks]

(b) The hydrocarbon has two structural isomers W and X that contain two benzene rings respectively. W exhibits geometrical isomerism but X does not. In their reaction with HBr, W forms Y that is optically active, while X forms Z that is optically non-active.

(i) Draw the geometrical isomers of W.

(ii) Draw the structural formulae of X, Y and Z.

(iii) Draw the structural formulae for the enantiomers of Y. [7 marks]

(c) Write balanced equations for the reactions of aminoethanoic acid with

(i) nitric(III) acid/ nitrous acid

(ii) sodium carbonate solution

(iii) ethanol in the presence of concentrated sulphuric [6 marks]

10 (a) Nitration of benzene is an electrophilic substitution reaction. Write the reaction mechanism of the nitration of benzene. In your answer, state the reagents and conditions of the reaction [5 marks ]

(b) The molecular formulae and some properties of two compounds K and L are given below. For each compound, identify a functional group which must be present and give the structural formulae of two possible isomers.

(i) K , C3H8O, gives white fumes of hydrogen chloride with phosphorus pentachloride.

(ii) L , C3H6O , gives an orange precipitate with 2,4-dinitrophenylhydrazine reagent.

For each pair of isomers K and L, give one chemical test that would enable you to distinguish between them, stating clearly how each isomer would behave.

[10 marks]

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