[done edu.joshuatly.com] pahang stpm trial 2011 chemistry (w ans)

8/13/2019 [Done Edu.joshuatly.com] Pahang STPM Trial 2011 Chemistry (w Ans)

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Section A

Four suggested answers labelled A, B, C and D are given for each question..Choose one

correct answer.

1. 71 g of Cl2 reacted with 1 g of H2 under standard conditions. How many molecules are present in the system at the end of the reaction?

[ L = 6.02 x 1023 mol−1 ]

A. 3.01 x 1023

B. 6.02 x 1023

C. 9.03 x 1023

D. 12.0 x 1023

2. The relative atomic mass of antimony , which consists of the isotopes 121Sb and 123Sb, is

121.8. What is the percentage of 123Sb in the isotopic mixture?

A. 40.0% B. 45.0% C. 50.0% D. 60.0%

3. A solid P has the following physical properties.

Insoluble in methylbenzene

Melts at 1300○C

Shows electrical conductivity in aqueous and molten states.

P maybe

A an atomic crystalB. an ionic crystalC. a molecular crystalD. a giant molecular compound

4. Which of the following species is deflected to the least extend in an electric field?

A. 27

13Al

3+ B 16

8O

2− C. 31

15P

3− D. 24

12 Mg2+

5. Ion X2+ contains 26 protons. What is the electronic configuration of X3+?

A. 1s22s

22p

63s

23p

63d

64s

2

B. 1s22s

22p

63s

23p

63d

54s

1

C. 1s22s22p63s23p63d8 D. 1s22s22p63s23p63d5

6. Which of the following species is not planar ?

A. BF3 B. NO3

− C. Al2Cl6 D. COCl2

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7. Equal masses ( 100g ) of each N2(g) and N2O(g) are injected into an empty container with a

fixed volume of 1 m3 at 25

○C. There is no chemical reaction between the two gases. Which

expression represents the total pressure of this container after the injection of gases?[ Relative molecular masses of N2 and N2O are 28.0 and 44.0 respectively.Gas constant, R, is 8.31 JK −1mol−1 ]

A.0.440.28

0.440.2829831.8100Pa

B.0.440.28

0.440.282531.82100Pa

C.0.440.28

29831.82100Pa

D.0.440.28

29831.8100Pa

8. Which of the following statements is true when a piece of magnesium ribbon is added to anaqueous solution of ammonium chloride?

A. Ammonia gas is evolved

B. Hydrogen gas is evolvedC. Chlorine gas is evolvedD. Magnesium chloride is precipitated.

9. The table below shows the data for the reaction between X and Y at a constant temperature.

Experiment [X]/ mol dm−3 [Y]/ mol dm−3 Initial rate/ mol dm−3

1 0.20 0.30 4.00 x 10−4

2 0.40 0.60 1.60 x 10−3

3 0.80 0.60 6.40 x 10−3

What is the rate equation for the reaction?

A. Rate = k [X]2[Y] B. Rate = k [X][Y]2 C. Rate = k [X]2 D. Rate = k [Y]2

10. A solution of 1.00 x 10−5

mol dm−3

of Ag+ ions is added slowly into an equal volume of

solution containing Cl− and Br − ions, each with the same concentration of 1.00 x 10−5 mol dm−3.[ The numerical values of K sp ( AgCl) and K sp ( AgBr) are 1.80 x 10−10 and 3.30 x 10−13

respectively ]

Which of the following statements is true about the reaction?

A. No precipitate is formed.B. AgBr is precipitatedC. A mixture of AgCl and AgBr is precipitated.

D. White precipitate formed , dissolves on adding excess solution of Ag+ ion.




11. The enthalpy change for the process represented by the equation:

Mg( s ) Mg2+

(g) + 2e−

is equal to

A. the second ionisation energy of magnesium.

B. the enthalpy change of sublimation of magnesium.C. the sum of the first and second ionisation energies of magnesium.D. the sum of the first and second ionisation energies and the enthalpy change of atomization of

magnesium.

12. A current of 8.0A is passed for 100 minutes through a solution of aqueous sulphuric acid

using inert electrodes. What will be the volume of gas liberated measured at room temperatureand pressure?

[ F = 9.65 x 104 C mol−1, 1 mol of gas occupies 24.4 dm3 at room temperature and pressure ]

A. 3.00 dm3 B. 6.00 dm3 C. 9.15 dm3 D. 12.0 dm3

13. Which of the following pair of liquids releases heat when mixed?

A. CH2Cl2 and (CH3)2CO

B. CHCl3 and C6H14 C. CCl4 and (CH3)2COD. CCl4 and CH3CH2OH

14. The standard enthalpy change of formation of but-1-ene, C4H8(g) and ethene, are x and

y kJ mol−1 respectively. Calculate the standard enthalpy change of the reaction2C2H4(g) C4H8(g) .

A. x – 2y B. 2y – x C. ½ ( x + y ) D. ½ ( y – x )

15. Which of the following statements does not explain why an aqueous solution of AlCl3 isacidic.

A. Cl− ion reacts with water to form HCl.B. Al

3+ion has high polarizing power.

C. The O – H bonds are weaker in [Al(H2O)6]3+ than in water.

D. [Al(H2O)6]3+ acts as an acid.

16. Which species does not act as a ligand in the formation of complexes?

A. Br − B. (CH3CH2)3 N C. NH4+ D. CN−

17. The following statements about the properties of graphite is true except

A. it can be used as a lubricant because of the weak forces of attraction between layers of

atoms.B. it is a good electrical conductor.C. the carbon to carbon distance between different layers is the same as that within each plane.D. each carbon atom is sp2 hybridised.




18. The rate equation for the reaction S2O8

2−(aq) + 2I−(aq) 2SO42−(aq) + I2(aq)

is Rate = k [S2O82−

(aq)][ I−(aq)], where k is the rate constant.

Which of the following statements is true about this reaction?

A. The value of k depends on the concentrations of S2O82−

and I− ions.

B. The reaction goes to completion.C. The reaction is first order with respect to S2O8

2− ion.D. The reaction is second order with respect to I− ion.

19. Which of the following solids has a macromolecular structure?

A. aluminium chlorideB. ice

C. magnesium oxideD. silicon(IV) oxide.

20. Which of the following statements is true regarding ammonia?

A. Ammonia forms the NH4OH molecule when dissolved in water.B. Ammonia gas is liberated on heating ammonium chloride.C. Aqueous ammonia reacts with copper(II)oxide to produce copper.

D. Ammonia reacts with oxygen,without the presence of a catalyst to form oxides ofnitrogen.

21. Aqueous aluminium chloride has a pH less than 7 because

A. the charge density of the aluminium ion is high

B. the aluminium ion undergoes hydrolysisC. aluminium chloride undergoes partial dissociation in waterD. aluminium chloride is a covalent compound.

22. A tetrachloride of Group 14,XCl4 has the following properties.

● It is easily hydrolysed● Unstable to heat● Decomposes at room temperature according to the equation

XCl4 → XCl2 + Cl2

X could be

A. germaniumB. carbonC lead

D. silicon




23. Which element forms the complex ion [XCl4]- ?

A. LeadB. CopperC. SiliconD. Chromium

24. A few types of glasses can be produced by the addition of metal and/or nonmetal oxides to silicates.Which of the following glasses has the lowestexpansion coefficient after the addition of metal and/or non metal oxides?

A. Borosilicate glass

B. Fused silica glassC. Soda glassD. Lime glass

25. The half-reaction of dichromate(VI) ion is shown as follows.

Cr 2O72- (aq) + 14H+ (aq) + 6e → 2 Cr 3+(aq) + 7H2O(l)

In one experiment, 45.0 cm3 of 0.2 mol dm-3 aqueous M2+ solution has

reacted with 15.0 cm3 of 0.1 mol dm-3 aqueous potassium dichromate(VI)solution. What is the oxidation state of M after the reaction ?

A. +3B. +4

C. +5D. +7

26. Which of the following best explains the action of a transition element as homogenouscatalyst?

A.It exhibits a variable oxidation stateB. It decreases the enthalpy of reaction.

C. It supplies energy to increase the rate of effective collision.D. It supplies electrons to facilitate adsorption through the formation of

temporary bonds.

27. An aqueous solution of X has the following properties.

(i) reacts with aqueous silver nitrate to form a precipitation

which dissolves in aqueous ammonia.

(ii) Reacts with aqueous barium hydroxide to form salt andwater.

(iii) Decomposes in the presence of sunlight to evolve a gas.




What could X be?

A. HCl and NH4Cl

B.

HCl and HOClC. HBr and HOClD. HBr and NH4Cl

28. Which of the following statements concerning alkenes ,P and Q are correct?

CH3CH2CH=CH2 CH3CH=CHCH3

A. Both P and Q shows cis-trans isomerismB. Both P and Q have the same boiling pointC. Both P and Q react with bromine to form 1,2-dibromobutane

D. P and Q react to form a polymer under suitable conditions

29. Which of the following molecule will react with butane under suitable conditions?

A. sodium ion

B. chloride ionC. chlorine atom

D. hydrogen atom

30. Consider the following reaction

+ CH3Cl

The benzene derivative reacts slower than benzene.R is most likely

to be

A. Cl atomB. SO3H group

C. CH3CH2 groupD. NO2 group

31. When 0.1 mole of a hydrocarbon Y is burnt in excess oxygen, 17.6 g of carbon dioxideis produced.0.1 mole of Y is found to react with 4.48 dm3 of bromine vapour under

standard conditions.What is the possible structural formula of X ?

[ Relative atomic mass : C=12,O=16.The molar volume of a gas is 22.4 dm 3 at stp]

A. CH2CH2CH2CH3 B. CH3CH=CH2 C. CH2=CHCH=CH2

D. CH2=C=C=CH2

X Cl R




32. Phenol is used to prepare the compound CH3COOC6H5 through an intermediate S asshown in the following scheme.

Reagent I Reagent IIC6H6OH S CH3COOC6H5

What is reagent I and II in the above scheme ?

What is reagent I and reagent II in the above scheme?

Reagent I Reagent II

A. PCl5 CH3COClB Na CH3COClC NaOH CH3COOH

D PCl5 CH3COOH

33. The compound C3H7I undergoes a sequence of reaction as follows.

KCN H2,PtC3H7I T U

in boil ethanol 150 C

What is the product U ?

A. CH3CH2CH2CNB. CH3CH2CH2 NH2

C. CH3CH2CH2CH2 NH2

D. CH3CH2CH2CH2CH3

34. The table below shows the boiling points of some haloalkanes.

Haloalkane Boiling point/C

CH3CH2Cl 12

CH3CH2Br 38

CH3CH2I 72

Which statement explains the difference in boiling point of the haloalkanes?

A. The strength of the bond increases in the order C-Cl ‹ C-Br ‹ C-IB. The polarity of the bond increases in the order C-Cl ‹ C-Br ‹ C-I

C. The size of the haloalkane increases in the orderCH3CH2Cl ‹ CH3CH2Br ‹ CH3CH2I

D. The reactivity of the haloalkanes increases in the orderCH3CH2Cl ‹ CH3CH2Br ‹ CH3CH2I




35. What could K and L be in the reaction below?

H20 C2H5OHK L CH3CH2 C O C2H5

Conc H2SO4

OK L

A CH3CH2CH2Cl CH3CH2COClB. CH3CH2CH2Cl CH3CH2COOHC. CH3CH2COCl CH3CH2COOH

D. CH3COCl CH3COOH

36. Which of the following hydroxyl compounds has

(a) the lowest pK a (b) the highest pK a value?

CH2OH OH OH OH O2 N OH N2O

CH3 Cl NO2

G H I J K

Lowest pKa value Highest pKa value

A. G J

B. H IC I J

D K G

37.Compound A has the following properties.

(i) it gives a positive iodoform test

(ii) it does not produce hydrogen chloride gas when treated with phosphorus pentachloride

(iii) it is oxidised by acidified KMnO4 to form carboxylic acidsunder suitable conditions.Compound A is most likely to be

A. CH3CH(OH)CH2CH3

B. (CH3)3COH

C. CH3CH2CHOD. CH3COC6H5




38. The scheme below shows the cycle of formation of an oily compound Z

NaOH(aq)+

∆

∆ HCl(aq)

SOCl2

The oily compound is

A.

B

C

D

39. The structural formulae of three organic compounds are given below.

CH3CH2CH2OH CH3CH2Cl CH3COOHM N O

Which sequence of compounds shows the order of increasing boiling points?

A. M ‹ N ‹ O B. N ‹ M ‹ O C. N ‹ O ‹ M D. O ‹ M ‹ N

40. Which of the following is made from thermosetting polymer?

A. FabricB. TyreC. Fire fighter jacket

D. Insulating tape for wires

C8H9 NO Oily

compound Z

CH3COONa

CH3COCl CH3COOH

NH2

NHCH3

CH2 NH2

CH2CH2 NH2




Bahagian B

For each of the questions in this section one or more of the three numbered statements1 to 3 may be correct.Determine which of the statements is correct.The responses A to

D should be selected on the basis of the following.

A B C D

Only 1 is

correct

Only 1 and 2 are

correct

Only 2 and 3 are

correct

1,2 and 3 are correct

41.The electrode potential value for the following cell

Pt(s) Br -(aq), Br 2 (l) Cl2(g) Cl-(aq) Pt(s)

Is influenced by

1. temperature

2. pressure3. concentration

42. Which of the following statements is true of HF,H2O and NH3 molecules?

1. All possess intermolecular hydrogen bonding2. The polarisability of the molecules increases in the order NH3,H2O and HF

3. The boiling points increase in the order HF,H2O and NH3

43.The solubility products of Ksp (at 298K) for Fe(OH)3 , MgCO3 and Ag2CrO4 are

8.0 x 10-40 mol4 dm-12 , 1.0 x 10-5 mol2 dm-6 and 3 x 10-12 dm-9 respectively.Which of the following mixtures will produce a precipitate?

1. 25 cm3 of 0.0003 mol dm

-3 FeSO4 and 75 cm

3 of 0.0001 mol dm

-3 NaOH

2. 25 cm3 of 0.001 mol dm-3 AgNO3 and 25 cm3 of 0.0001 mol dm-3 K 2CrO4

3. 50 cm3 of 0.001 mol dm-3 MgSO4 and 25 cm3 of 0.002 mol dm-3 Na2CO3

44. The table below shows the changes in pressure with temperature at constant volumefor three gases P,Q and R.

Gas Pressure/atm

At 300K At 350 K At 400 K At 450KM 1.00 1.17 1.33 1.50

N 1.00 1.51 2.10 2.32

O 1.00 1.87 2.35 2.93

Which gases show deviation from the ideal behaviour?1. M 2. N 3. O




45. An aqueous solution of the sulphate of a metal M is electrolysed using metal M as theelectrodes X and Y

When a current of 0.483 A is passed through the electrolyte for 1000 seconds, themass of cathode increases by 0.120 g.Which of the following statements are correct

with regard to the electrolysis?

[ Relative atomic mass of M = 48.0,Faraday constant F = 96500 C mol -1]

1. A total of 0.483 x 103 F have passed through the electrolyte.

96 5002. The mass of electrode X decreases by 0.120g3. The reaction taking place at electrode Y is M3+ (aq) + 3e → M(s)

46. Which isomerism is shown by the complex ion Co(NH3)3Cl3 ?

1. Mer-fac

2. Optical3. Cis-trans

47.In catalytic converters,platinum/platinum/rhodium is used to catalyse

1. the oxidation of sulphur dioxide to sulphur trioxide2. the oxidation of hydrocarbons to carbon dioxide and water.3. the reduction of the oxides of nitrogen to nitrogen and oxygen.

48. Aqueous nickel(II) nitrate contains the [Ni(H2O)6]2+ complex ion that is

green.Addition of an excess of a bidenmtate ligand byethylenediamine,NH2CH2CH2 NH2,to the solution causes the colour to change to

purple.Which of the following statements are true regarding the process?

1.The change in colour shows that the ethylenediamine ligand forms a complex ionwith nickel(II)

2. Ethylenediamine is a stronger ligand than water.

3. The purple solution contains the [ Ni ( NH2CH2CH2 NH2)6]2+

complex ion

X(metal M)(metal M) Y




49. When R is substitured into the benzene ring of phenol,the acidity of phenolincreases.R is

1.–NO2

2.–Cl3.–CH3

50. Which of the following statements are true regarding polymerization that uses Ziegler- Natta catalyst?

1.The polymerisation process involves free radicals.2.The polymerisation involved is addition polymerisation.3.The polymerisation process produces high density polymers.

END OF QUESTIONS




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* This question paper is CONFIDENTIAL until the examination is over. CONFIDENTIAL*

Identity card number........ ........... .......... ........... ........ Centre number/index number :…………………………………

(Nombor kad pengenalan) (Nombor pusat/angka giliran)

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TRIAL STPM 2011(PEPERIKSAAN PERCUBAAN STPM 2011)

CHEMISTRY (KIMIA)

PAPER 2 (KERTAS 2)

Two and a half hours (Dua jam setengah)

For examiner’s use

1

2

3

4

5

6

7

8

9

10

Total

This question paper consists of 12 printed pages.

Instructions to candidates:

DO NOT OPEN THIS QUESTION PAPER UNTIL

YOU ARE TOLD TO DO SO.

Answer all questions in section A. Write your answers in the

spaces provided. All working should be shown. For numericalanswers, units should be quoted wherever they are appropriate.

Answer any four questions in section B. 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 question paper .




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Section A [ 40 marks ]

Answer all questions in this section.

1. (a) Draw and name the shape of these following molecules :

(i) BeCl2

Shape :

(ii) CO32-

Shape :

(iii) NH4+

Shape :

(iv) SF6

Shape :

[ 4 marks ]




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(b) An element A reacts with another element B to form a compound of formula AB2. Theelement B exist as molecules of formula B2. Some properties of A, B2 and AB2 are

tabulated below:

Substance A B2 AB2

Melting pointHigh

(in the range of

700°C - 1200°C)

Very low(less than -50°C)

Moderate(in the range of

400°C -700°C)

Electrical conductivityof the salt High Very low Very low

Electrical conductivityof molten material High Very low

High

Electrical conductivity

of aqueous solution

of the material

- -High

(i) Which particles will move when a potential difference is applied across a sampleof

(I) solid, [ 1 marks ]

…………………………………………………(II) molten AB2 ? [ 1 marks ]

…………………………………………………

(ii) Explain why the electrical conductivity of molten AB2 is high, whereas that of thesolid is very low. [ 2 marks ]

………………………………………………………………………………….

………………………………………………………………………………….

(iii) Electrolysis of an aqueous solution of AB2 with Pt electrodes give A at the cathodeand B2 at the anode. Suggest possible name for the elements A and B 2 consistent

with all the above information.

[ 2 marks ]

A : ………………………………. B2 : ……………………………..




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2. As a first step in a manufacture of nitric acid it has been suggested that nitrogen monoxide NO, can be formed from nitrogen and oxygen in a reversible reaction.

(a) Write an equation for this reaction and deduce an expression for the

equilibrium constant K c. [ 2 marks ]

Equation

………………………………………………………………………….

K c =

(b) The sketch graph below shows how the value of K c for this reaction changes

with temperature.

Kc

Temperature (ºC)

Use this graph to deduce whether the reaction is exothermic or endothermic.

Explain your answer. [ 2 marks ]

.…………………………………………………………………………………

…………………………………………………………………………………..




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(c) When cooled, nitrogen monoxide reacts with oxygen to form gaseous nitrogen dioxide NO2, in a

reversible reaction.

(i) Write an equation for this reaction. [ 1 mark ]

………………………………………………………………………………………..

(ii) State how an increase in pressure would change the position of the equilibrium and the

value of the rate constant for this reaction. [ 2 marks ]

Change in equilibrium position :

………………………………………………………………………………………..

Change in rate constant :

………………………………………………………………………………………..

(d) Titration curves labelled A, B, C and D for combinations of different acids and bases are

shown below. All solutions have a concentration of 0.1 mol dm –3

.

14

12

10

8

6

4

20

pH

0 10 20 30 40 50

Volume/cm3

A

14

12

10

8

6

4

20

pH

0 10 20 30 40 50

Volume/cm3

B

14

12

10

8

6

4

2

0

pH

0 10 20 30 40 50

Volume/cm3

C

14

12

10

8

6

4

2

0

pH

0 10 20 30 40 50

Volume/cm3

D




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(i) Select from A, B, C and D the curve produced by the addition of

ammonia to 25 cm3 of hydrochloric acid [ 1 mark ]

......................................................................................................................

ethanoic acid to 25 cm3

of sodium hydroxide [ 1 mark ]

......................................................................................................................

(iii) A table of acid–base indicators and the pH ranges over which theychange colour is shown below.

Indicator pH range

Thymol blue 1.2 – 2.8

Bromophenol blue 3.0 – 4.6

Methyl red 4.2 – 6.3

Cresolphthalein 8.2 – 9.8

Thymolphthalein 9.3 – 10.5

Select from the table an indicator which could be used in the titration which produces curve A but not in the titration which produces curve B. [ 1 mark ]

..............................................................................................................................




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3. (a) (i) Write the electron configuration of the Scandium atom and Scandium (III) ion, Sc3+

.

[ 2 marks ]Sc :……………………………………………………………………..

Sc3+ :

……………………………………………………………………..

(ii) State the colour of Scandium (III) ion, Sc3+

and explain why the colour is such.

[ 2 marks ]

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

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

(b) Chlorine is a greenish yellow poisonous gas which is slightly soluble in water.

(i) Write a balanced equation for the reaction that occur when chlorine gas is passed into water.

[ 1 mark ]

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

(ii) What would you observe when an excess of potassium iodide is added to the solution obtained

from the reaction and write the equation that occurs. [ 2 marks ]

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

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

(c) A sodium halide reacts with cold concentrated sulphuric acid to give colourless fumes.Whenheated, the mixture produces brown fumes.

(i) Name the halide ion in the sodium salt. [ 1 mark ]

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

(ii) Write two balanced equations to explain the observations above. [ 2 marks ]

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

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




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(c) When N is heated with concentrated sulphuric acid, a colourless liquid P is obtained. Pdecolourises bromine water. [ 3 marks ]

(i) Draw the structural formula of P.

(ii) What is the type of reaction that occurred in the conversion of N to P?

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

(iii) When P is heated with a catalyst, a viscous liquid with high relative molecular is produced by addition polymerization. Draw the repeating unit of the substance in the viscous liquid.




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Section B [ 60 marks ]

Answer any four questions in this section.

5. (a) A The reaction : 2NO(g) + Cl2(g) 2NOCl was studied at -10°C, and thefollowing data were obtained :

Eksperiment Number

Initial

concentration

[NO], mol dm-3

Initial

concentration

[Cl2], mol dm-3

Initial rate of formation of NOCl, mol dm

-3 min

-1

1 0.10 0.10 0.18

2 0.10 0.20 0.35

3 0.20 0.20 1.45

What is the order of reaction with respect to NO and with respect to Cl2 and what is

value of the rate constant ? State clearly the units of rate constant.

[ 4 marks ]

(b) Sucrose decomposes in acid solution into glucose and fructose according to a first

order rate law, with a half-life of 3.33 h at 25°C. What fraction of a sample of sucrose

remains after 9.00 h ? [ 3 marks ]

(c) A current of 2.00 A is passed through a potassium sulfate solution for 30.0 minutes at

25.0°C using graphite electrodes. Calculate the volume, in cm3, of the gas evolved at

the anode at 101 kPa. [ 3 marks ]

(d) The values of Ksp for the slightly soluble salts MX and QX2 are each equal to

4.0 x 10-18

. which salt is more soluble ? Explain your answer fully. [ 5 marks ]

6. (a) Elements P and Q form an ionic compound PQ. The enthalpy changes involved in the

formation of this compound under standard conditions are as below :

P(s) P(g) : ∆H° = +77 kJ

½ Q2(g) Q(g) : ∆H° = +121 kJ

P(g) P+(g) + e

- : ∆H° = +419 kJ

Q(g) + e- Q

-(g) : ∆H° = - 364kJ

P(s) + ½Q2(s) PQ(g) : ∆H° = -436 kJ

Write equation which represent the lattice energy of compound PQ and calculate

the value of the lattice energy with the aid of a Born-Haber cycle. [ 6 marks ]

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

cities. Suggest how NO2 is formed in a car engine and how it may be removed from

exhaust gases.[ 3 marks ]




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(c) In the gaseous state, NO2 can dimerise as follows.

(i) 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

mass, Mr of the mixture.[ 3 marks ]

(ii) at another temperature, it is found that the partial pressures of NO2 and N2O4 atequilibrium are 0.4 atm and 0.6 atm respectively.

Write an expression for Kp and calculate its value, giving units. [ 3 marks ]

7. Benzene and methylbenzene form a solution that obeys Raoult’s law. The vapour pressure

of pure benzene and pure methylbenzene are 12.7 and 3.9 kPa respectively at 298 K.

(a) State Raoult’s law [ 2 marks ]

(b) Draw and label, on a graph paper the vapour pressure-composition graph for a mixture

of benzene and methylbenzene. [ 3 marks ]

(c) Determine the vapour pressure of a solution containing 2.0 moles of benzene and 3.0

moles of methylbenzene. [ 3 marks ]

(d) By using a sketch of boiling point-composition curve, describe how a mixture of

benzene and methylbenzene can be separated. [ 7 marks ]

8. (a) State the changes in acid-base properties of oxides of the third period elements, that is fromsodium to chlorine in the Periodic Table. Write an equation to represent each typical property

of the oxides. [ 6 marks ]

(b) Between hydrogen chloride and hydrogen sulphide, which is the stronger acid in aqueoussolution. Explain your answer.

[4 marks ]

(c) Draw the possible structures of isomers of the following complexes. State the name of eachisomer.

(i) [Cr(NH3)4Cl2]+

(ii) [Cr(C2O4)3]3- [ 5 marks ]




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9. Two organic compounds X and Y have the following formulae.

O2 N CH3 H2 N COOH

X Y

a) State which of these two compounds has the higher melting point. Explain your answer.[ 3 marks ]

b) State the reagents used and the conditions, the observations obtained and write equations forthe reactions that occur for the following.(i) Formation of X from benzene. [ 4 marks ]

(ii) Formation of Y from X. [ 4 marks ](iii) A simple test to differentiate between X and Y. [ 2 marks]

c) Which of the compounds X and Y exists as a zwiterrion? Write the formula of the zwiterrion.

[ 2 marks ]

10. a) Explain the following observations and write equations for the reactions involved.(i) 1-Butanol is insoluble in aqueous sodium hydroxide but phenol is soluble. [ 3 marks ]

(ii) Methanoic acid decolourises the purple colour of aqueous potassium manganate( VII).[ 3 marks ]

(iii) Methylamine is soluble in hydrochloric acid.[ 2 marks ]

b) Using 1, 4-dibromobutane, Br(CH2)4Br, as the starting material, write the equations

for all the reactions involved in the synthesis of nylon-6,6. [ 7 marks ]

END OF QUESTION PAPER




1

MARKING SCHEME OF PAPER 2 CHEMISTRY TRIAL STPM 2011

1. (a)

(i)BeCl2

Cl Be Cl

Shape : linear

(ii)CO32-

O

||

C

-

O O-

Shape : trigonal planar

(iii) NH4+

H+

N

H H

H

Shape : tetrahedral

(iv) SF6

F

F F

S

F

F

F

Shape : octahedral

[4M]

(b) (i) electrons

Ions / A2+

and B- [2M]

(ii) Ions in molten AB2 can move freely, [1M]

in solid ions are held closely in a lattice position. [1M]

(iii) A: Mg B2:Cl 2 [2M]

-------------------

Total : 10M




2

2. (a) Equation N2 + O2 2NO (1)

K c = [NO]2 [N2] [O2] (1) [2M]

(b) As temperature increases K c increases (or yield increases) (1)

Hence reaction endothermic (1) [2M]

(c) (i) 2NO + O2 2NO2 (1)

(ii) Change in equilibrium position: Displaced to the right (1)

Change in rate constant: No change (1) [3M]

(d) (i) B; (1) C; (1) [2M]

(ii) cresolphthalein OR thymolphthalein; [1M]

--------------

Total : 10 M

3. (a) (i) Sc : 1s2 2s2 2p6 3s2 3p6 3d1 4s2 [1M]

Sc3+ : 1s2 2s2 2p6 3s2 3p6 [1M]

(ii) Sc3+ is a colourless ion [1M]

because there is no electron in 3d subshell [1M]

(b) (i) Cl2 + H20 HCl + HOCl [1M]

(ii) Brown precipitate of iodine is formed, iodine is oxidised [1M]

Cl2 + 2I- 2Cl

- + I2 [1M]

(c) (i) Sodium bromide [1M]

(ii) NaBr + H2SO4 NaHSO4 + HBr [1M](iii) 2HBr + H2SO4 SO2 + Br 2 + 2H2O [1M]

-----------------

Total : 10 M

4. (a) (i) C H O

80.0 6.7 13.3

12 1 16

= 6.67 = 6.67 = 0.83

8 8 1

Empirical formula : C8H8O [1M]

(ii) pV = nRT

101 x 0.1 = n (8.314) x 480

n = 0.025

RMM of M is 0.305 = 122 [1M]

0.025

Molecular formula of M : C8H8O [1M]

(b) (i) triiodomethane [1M]

(ii) M has carbonyl group [1M]

N is an alcohol [1M]

(iii) M :

CO CH3 [1M]




3

N : CH(OH)CH3 [1M]

(c) (i) P: CH=CH2 [1M]

(ii) Dehydration [1M]

(iii) –CH-CH2- [1M]

------------------

Total : 10M

5. (a) From expt 1 and 2 to determine the order with respect to Cl2,

( 1.0 )m = 0.18 ; (½ )

m = ½ ; [1M]

0.2 0.35

m ≈ 1 , the reaction is first order with respect to Cl2

From expt 2 and 3 to determine the order with respect to NO,

( 1.0 )m = 0.35 : (½ )

m = ¼ ; [1M]

0.2 1.45

m ≈ 2 the reaction is second with respect to NO

Rate = k[NO][Cl2]2 [1M]

From expt 1,

0.18 = k(0.10)(0.10)2

k = 180 mol

-2

dm

6

[1M]

(b) ln[sucrose] = -kt + ln[sucrose]0

(1) ln[0.5] = - k (3.33) + ln[1](2) ln[sucrose] = - k (9) + ln[1] [1M]

(2) ÷ (1)

ln[sucrose] -k(3.33)

-------------- = -------------

ln[0.5] -k(9)

[sucrose] = 0.153 [1M]

Fraction remaining = 0.153/1 =0.153 [1M]

(c) Q = It = 2.00 x 30 x 60 =3 600 C

Anode – oxygen gas

4OH- ----- > 2H2O + O2 [1M]

1 mol O2 requires 4F

3 600 C = 3600 mol of O2 = 0.00933 mol [1M]

4 x 96500Volume of O2 produced = 0.00933 x 24 = 0.224 dm3 [1M]




4

(d) MX M+ + X-

Ksp = [M+][X

- ] = 4.0 x 10

-18 [1M]

The solubility of MX = [M+] = 2.0 x 10

-9 [1M]

QX2 Q2+

+ 2X-

Ksp = [Q2+

][X- ]

2 = 4.0 x 10

-18 [1M]

The solubility of MX = [M+] = 1.0 x 10

-6 [1M]

QX2 is more soluble [1M]

---------------

Total : 15M

6. (a)

P+(g) + Q

-(g)

∆H° = +419 kJ ∆H° = - kJ

P(g) + Q(g) :

∆H° = +77 kJ ∆H° = +121 kJ

P(s) + ½Q2(s)

∆H° = -436 kJ

PQ(g)

P+(g) + Q

-(g) PQ(g) : ∆H° = lattice energy [4M]

Lattice energy = -436 – 77 – 121 – 419 - (-364) [1M]

= - 689 kJ/mol [1M]

(b) The temperature in the car engine is very high. [1M]

The high temperature cause the N2 and O2 in the air to react to form NO2. [1M]

NO2 can be removed form exhoust gaswes by using catalytic converter which

reduce NO2 to N2. [1M]




5

(c) (i) Let n be the number of mol of gasseous molecules present.

PV = nRT

1.0 x 105 x 190 x 10-6 = n x 8.31 x 320 [1M]

n = 0.00714 [1M]

average mass = mass ÷ mol

= 0.5 ÷ 0.00714

= 70.0 [1M]

(ii) PN2O4

Kp= ---------------- [1M]

PNO2

0.6Kp = --------------- = 3.75 atm

-1 [2M]

(0.4)2

7. (a) the vapour pressure PA of a liquid in a mixture of a miscible liquids is given by

the products of the vapour pressure of that pure component P°A and its mole fraction

PA = XAP°A [2M]

(b) pressure/kPa

12.7

P(t)

3.9 P(benzene)

P(methylbenzene)

0 1

Mol fraction of benzene [3M]




6

Partial pressure of benzene in the mixture = 2/5 x 12.7 = 5.08 kPa [1M]

Partial pressure of benzene in the mixture = 3/5 x 3.9 = 2.34 k [1M]

Total pressure = 7.42 kPa [1M]

(c) A mixture of benzene and methylbenzene which forms an ideal solution, can be [1M]

separated by fractional distillation. Benzene, which is more volatile, will be

distilled over first, followed by methylbenzene.

Temperature/°C

Boiling point

vapour of benzene

Boiling point

of methyl

benzene

liquid

0 1.0 [2M]

mol fraction of benzene

A mixture of benzene and methylbenzene with C1 composition is being heated [1M]

to boil at T1 temperature.

This will produce a vapour with C2 composition which has more benzene.

The vapour will be cooled in the column and become liquid. [1M]

A mixture of benzene and methylbenzene with C1 composition Reheating willvapourise the C2 liquid to form vapour at T2 temperature with C3 composition [1M]

which even rich in benzene.

Repeating processes of boiling, cooling and condensation will separate benzene [1M]

as distillate and methylbenzene as residue ----------------

Total: 10M

8. (a) Na2O and MgO are basic oxides. [1M]

MgO is insoluble in water but it is soluble in dilute acid

Na2O + H2O 2NaOH

MgO + 2HCl MgCl2 + H2O [1M]Al2O3 is amphoteric. It dissolves in both dilute acids and alkalis [1M]




7

Al2O3 + 6H+ 2Al3+ + 3H2O [1M]

Al2O3 + 2OH-

+ 3H2O 2Al(OH)4

-

The other oxides like SiO2, P4O10, SO3 and Cl2O7 are all acidic [1M]

They dissolve in water to produce acidic solutions.

SO3 + H2O H2SO4 [1M]

(b) HCl is stronger acid in aqueous solution [1M]

The H-Cl bond is more polar than the H-S bond. Cl is more electronegative than S [1M]

H-Cl ionises completely whereas H2S ionises only partially in aqueous solution. [1M]

HCl + H2O H3O+ + Cl

-

H2S + H2O H3O+ + HS

- [1M]

(c)

[1M + 1M]

Cis Trans [1M]

[1M + 1M]

---------------

Total : 15M

Mirror

9. (a) Y [1M]

Because molecules of Y form intermolecular hydrogen bonds whereas the [1M]Intermolecular forces between molecules of X are the weak van der Waals

forces. [1M]

(b) (i) Step 1

Reagent: Chloromethane in the presence of anhydrous aluminium chloride [1M]

Equation : H + CH3Cl CH3 + HCl [1M]

Step 2

Reagent: Concentrated sulphuric acid and concentrated nitric acid [1M]Condition : 550C

Cl

NH3 H3N

Cl

+

NH3 NH3

Cr Cr

Cl

NH3 H3N

+

ClNH3 H3N

Cr

3-

OO

O

O

OO

C

C

C

C

C C

O

O

O

O

O

O

Cr

3-

OO

O

O

O

O

C

C

C

C

C

C

O

O

O

O

O

O




8

Equation: CH3 + HNO3 H3C NO2 + H2O [1M]

(ii) Step 1

Reagent: Add tin, concentrated HCl followed by NaOH (aq) [1M]

Equation : O2 N CH3 + 6[H] H2 N CH3 + 2H2O [1M]

Step 2

Reagent: Acidified potassium manganate (VII) solution and reflux [1M]

Equation : H2 N CH3 + 3[O] H2N COOH + H2O [1M]

(iii) Y will dissolve in hydrochloric acid whereas X will not. [1M]

HOOC NH2 + HCl HOOC NH3Cl [1M]

(c) Y [1M]

H3+ N n COO

- [1M]

---------------

Total : 15 M

10. (a) (i) The benzene ring has electron withdrawing effect, this makes the O-H

group bond quite polar to donate proton. With NaOH (aq) phenol forms

a stable salt of sodium phenoxide. [1M]

On the other hand, 1-butanol is neutral. The butyl group is rather non-polar [1M]

And this prevent its reaction with NaOH (aq).

OH + NaOH ONa + H2O [1M]

(ii) Methanoic acid contains aldehyde group in its structure. Hence just like [1M]

aldehydes it can be oxidised by acidified potassium manganate (VII) [1M]

solution to carbonic 1M

acid which decomposes to carbon dioxide and water.

H –C=O + [O] H2CO3 CO2 + H2O [1M]OH

(iii) Methylamine is a base solution and will react with dilute HCl to produce [1M]

A water-soluble ionic salt.

CH3 NH2 + HCl CH3 NH3Cl [1M]




(b) NaCN (alcohol), reflux

Br(CH2)4Br NC(CH2)4CN [1M]

Dilute H2SO4 [1M]

reflux

HOOC(CH2)4COOH [1M]

NaCN (alcohol), reflux Br(CH2)4Br NC(CH2)4CN [1M]

LiAlH4, H2O/H+ [1M]

ether

H2 NCH2(CH2)4CH2 NH2 [1M]

n [H2 NCH2(CH2)4CH2 NH2] + n [HOOC(CH2)4COOH] [1M]

---------------

Total : 15 M

[done edu.joshuatly.com] pahang stpm trial 2011 chemistry (w ans)

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