paper 2 marking scheme 2013

7/27/2019 Paper 2 Marking Scheme 2013

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SPM TRIAL EXAMINATION 2013

MARA JUNIOR SCIENCE COLLEGE

CHEMISTRY

Paper 2

MARKING SCHEME

FOR EXAMINERS USE ONLY

The marking scheme consists of 18 printed pages


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MARKING GUIDELINES

SPM TRIAL EXAMINATION 2013

PAPER 2

Symbol Meaning

// - replace the whole sentence

( ) - replace the previous word

[ ] - can be summarized from explanation

___ or bold - key word

a.d.p - avoid double penalty

wcr - wrong cancel righta. - accept

r. - reject

e.c.f - error carry forward

/ - or


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1 (a) (i) Type : Flavouring agentFunction :To improve the taste/aroma of food

(ii) Reduce the effect of insect bites/headache/nausea/windycondition/stomach discomfort/pain of toothache/sprains

//antibacterial/antifungus (a: any suitable answer)

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(b) (i) Contact Process

(ii) 1. Sulphur

2. Oxygen

(iii)Name : Ammonium Sulphate( r. Formula : (NH4)2SO4 )

(iv)Detergent does not form scum/insoluble salt / precipitate(v) Sulphur dioxide react with rain water to produce acid rain /

can cause respiratory problems

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TOTAL 9


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2 (a) Gas 1 1

(b) Aluminium // Al 1 1

(c) (i) 2.8.8 / 2,8,8

(ii) Atom has 8 valence electrons //

atom achieved octet electron arrangement

(r : stable electron arrangement)

1

1 2

(d) (i) 1. Attraction / Van der Waals force between molecules /intermolecular forces of carbon dioxide is weak

2. Less heat needed to overcome the forces

( r : particles )

(ii) C + O2 CO2

(iii) 1. Correct electron arrangement of C and O

2. Label nucleus and correct number of shared electrons

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TOTAL 9

CO

O


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3 (a) (i) To allow the movement / flow of ions(ii) Magnesium // Mg(iii) Magnesium is more electropositive than copper

// Position of magnesium is higher than copper in the

Electrochemical Series // Magnesium atom donates electrons

// Magnesium oxidized // Oxidation number of magnesium

increases from 0 to +2

( r : more reactive / ECS )

(iv) Reduction

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(b)

(i) 1. Correct position of iron ring and silver plate

2. Label (iron ring and silver plate)

* P2 dependent on P1

(ii) Grey solid deposited on the iron ring // silver plate becomes

thinner

(iii) Iron ring : Ag+ + e Ag

(iv) 1. Remain unchanged

2. The rate of discharge of Ag+ at cathode is same as the rate

of ionisation of Ag atom at anode // the number of Ag+

discharge /reduce at cathode is same with the number of

Ag+ formed at anode // each Ag+ discharged at cathode

is replaced by one Ag+ ion produced at anode

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TOTAL 10

Ironring

Silverplate


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4 (a) (i) Change in quantity of reactant / product per unit time //Change in quantity of reactant/product

Time taken

(ii) Size / Total surface area of zinc

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(b)

Zn + 2H+ Zn2+ + H2

1. Correct formulae of reactants and product

2. Balanced equation

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(c) (i)

(ii) 50 cm3

/ 60s = 0.833cm3

s-1

// 50 cm3/ 1 min = 50 cm3 min-1

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1

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(d) The presence of catalyst/copper(II) sulphate solution in

Experiment III lowers the activation energy

More colliding particles able to achieve the low activation energy

Frequency of effective collision between H+ ions and zinc atoms

is higher

(r: increases)

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TOTAL 10

III III


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5 (a) Heat released when 1 mol of water is produced from

neutralisation of acid and alkali.1

1

(b) (i) Average initial temperature = 28.0 + 29.0 = 28.5oC

2

Heat released = (50 + 50) 4.2 (41.528.5)

= 100 4.2 13.0

= 5460 J

(ii) mole of HCl = 2.0 50 = 0.1 mol

1000

(iii) 1. 0.1 mol of water / H2O release 5.46 kJ heat

2. 1 mol of water / H2O release 5.460 = 54.6 kJ0.1

3. H = - 54.6 kJ mol-1

*(ecf for point 1 only)

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(c)

Energy

HCl + KOH

H = - 54.6 kJ mol-1

KCl + H2O

1. Energy axis and two energy level is drawn correctly

2. Correct chemical formula of reactant and product , H

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1 2

(d) 1. Ammonia is a weak alkali / dissociate partially in water

2. some heat is absorbed to dissociate ammonia molecules

completely

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(e) Plastic cup // paper cup // ceramic /porcelain cup // 1 1

TOTAL12

Max 11


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6 (a) (i) Hydrogen ion

(ii) 1. Without/Absence of water ,2. hydrogen chloride exist as molecules //no hydrogen ions

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(b)

(i) Acid L : ethanoic acid/[any organic acid]

[a: formula]

(ii) 1. Hydrochloric acid is strong acid / ionise completely in water

2. Concentration of hydrogen ions is higher

*If : 1. Acid L is a weak acid / ionise partially in water

2. Concentration of hydrogen ions is lower

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(c) (i) CaCO3 + 2 HCl CaCl2 + CO2 + H2O

- Correct formula of reactants and products

- balanced equation

(ii) 1. Mole of CaCO3 = 1 /100 = 0.01 mol

2. 1 mole of CaCO3 produce 1 mole of CO20.01 mol of CaCO3 produce 0.01 mole of CO2

3. Volume of CO2 = 0.01 x 24 = 0.24 dm3 / 240 cm3

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TOTAL 11

0+1


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SUB TOTAL

7 (a)(i)

(ii)

Able to state the physical state of W at room condition correctlyAnswer

Solid

Able to give reason correctlyAnswer

The room temperature is below the melting point.

Able to sketch a graph of temperature against time for the

heating1. Both axes with units correctly

2. Correct shape of curve

3. Show the melting of substance W on your graph

Answer

( r : sharp edge of the curve )

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1

1

1

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2

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Time ( min or s)

119 C

Temperature (0 C)


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(b)(i)

(ii)

(iii)

Able to write the meaning of isotopes correctly

Answer

Isotopes are atoms of carbon with same number of protons

/ 6 protons but different number of neutrons / 6 or 8 neutrons.

orIsotopes are atoms of carbon with same proton number but

different nucleon number

Able to state one usage for isotope of carbon-14 correctly.

Answer

To estimate the age of fossils / artefact // carbon dating

Able to compare the number of subatomic particles are present

in the atoms carbon-12 and carbon-14.

Answer

Carbon-12 Carbon-14

Number of proton 6 6

Number of neutron 6 8

Number of electron 6 6

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4

(c) Able to write a balance chemical equation correctly

Answer

C + 2 CuO 2 Cu + CO2

1. Correct formula of reactant and product


Able to calculate the mass of copper correctly

Answer

1. mole of CuO = 4 = 0.05 mol

64 + 16

2. 2 mol of CuO produce 2 mol of Cu

0.05 mol of CuO produce 0.05 mol of Cu

3. Mass of Cu = 0.05 x 64 = 3.2 g

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(d) Able to state the type of particles present in the solution when

purple colour is observed correctly.

Answer

1. Molecules / water molecules

2. Ions / manganate ions

Able to explain the observation based on the kinetic theory of

matter.

Answer

1. water/ potassium manganate is made up of tiny/small and

discrete particles and move randomly/freely

2. At higher temperature particles move faster/ higher speed /gain

higher kinetic energy

3. particles/ions of potassium manganate diffused/ spread more athigher temperature into water

4. from higher concentration to lower concentration of potassium

manganate

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Max 3

Total 20


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Question Mark schemeSub

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Total

Mark

8 (a)

(b)

Able to state the general formula, the functional group

and the homologous series for these compounds

correctly.

Sample answer

Compound S T

General

formula

C n H 2n ,

n = 2,3,..

C n H 2n+1 OH ,

n= 1,2,3..

Functional

group

C=C

or

carbon double bond

-OH

or

hydroxyl group

Homologous

seriesAlkene Alcohol

Notes

(a: in a table // without a table)

Able to write the balanced chemical equation for the

reaction correctly

1. Correct formula for reactants and products


Sample answer

C4 H9 OH + 6 O2 4CO2 + 5H2 O

Able to calculate the volume of carbon dioxide gas

3. Mole of C4H9OH

4. Mole of CO2

5. Volume of CO2 with correct unit

Sample answer

3. Mol of C4H9OH =

= 0.25 mol

4. 1 mol of C4H9OH produce 4 mol of CO2

0.25 mol of C4H9OH produce 1 mol CO2 gas

5. Volume of CO2 gas = 1 x 24 dm3 // 24 dm3

1+1

1+1

1+1

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Total

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(c)(i) Able to explain the difference in the observation

Sample answer

Experiment I Experiment II

1. Coagulation occurs 2. No coagulation

3. Rubber molecules enclosed by a protein membrane

which is negatively charged

4. Bacteria from the air

enter the latex and

produced lactic acid/ acid

Ammonia solution

contains hydroxide ion //

OH-

5. The hydrogen ions, H+

neutralize the negatively

charges on the proteinmembrane

OH- ion neutralized the

acid produced by the

bacteria

6. The rubber particles

collide with each other

and break the

membrane, rubber

molecules combined

Rubber particles remains

negatively charged

1+1

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(c)(ii) Able to explain how the vulcanization of rubber

improve the weakness of natural rubber

Sample answer

1. Sulphur atom

2. make a cross- linkages between rubber molecules

3. reduce the rubber molecules from sliding

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Total 20


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9 (a)(i)

(ii)

(iii)

Able to name the solution from the list that react

with sodium hydroxide solution to form white

precipitates and dissolve in excess of sodium

hydroxide solution.

Sample answer

1. Aluminium nitrate2. Lead(II) nitrate3. Zinc nitrate

Able to name a white precipitates formed and write

the ionic equation

Sample answer

1. Aluminium hydroxide / Lead(II) hydroxide /zinc hydroxideSample answer

Al3+ + 3OH- Al(OH)3or

Pb2+ + 2OH- Pb(OH)2

or

Zn2+ + 2OH- Zn(OH)2

Able to name any two of the solutions to prepareinsoluble salt

Sample answer

Sodium carbonate + (any other solutions)

// Lead(II) nitrate + magnesium sulphate //

Calcium nitrate + magnesium sulphate

*(a : name of solutions given in procedure)

Able to describe how the salt is prepared in the

laboratory correctly.

(For any of the pair of solutions mentioned above)

Sample answer

Procedure:

1. (20-100) cm3 of (0.1- 2.0) mol dm-3 sodium

carbonate solution is poured into the beaker

2. (20-100) cm3 of (0.1- 2.0) mol dm-3 lead(II) nitrate

solution is added .

* [adp for concentration and volume if didnt mention in

P1 and P2but word into a beakermust present]

3. [Stir the mixture]4. Filter

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5. Wash/rinse the residue/solid/PbCO3 / salt/ precipitate

Able to write a balanced chemical equation

correctly:

Sample answer

Na2CO3 + Pb(NO3)2 PbCO3 + 2NaNO3

1. Correct formula of reactants and products


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(b) Able to describe chemical tests to verify the presence

of zinc ion , chloride ion and sulphate ion.

Sample answer

* Test for zinc ion:

1. Add a small amount / drop by drop ammoniasolution until excess into solution

2. White precipitate is formed and dissolve in excess3. *Zn2+ ion present(*P.3 : can infer from title of the test)

Test for anion ion:**4. Pour the two solution into two different test tubes.

5. Add nitric acid followed by silver nitrate solution

into each test tube.6. The solution that produce white precipitate contains

chloride ions

**Pour the other solution into a test tube

7. Add hydrochloric acid followed by barium chloride

solution

8. White precipitate formed confirmed that sulphate

ion present .

(** Both steps for P4)

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Max 7

Total 20


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10 (a)(i)

(ii)

(iii)

Able to name halogen X correctly

Sample answerChlorine // Bromine

[r: chemical formula]

Able to write the half equation correctly1. Correct formula for reactants and products


Sample answer

Half equation of reduction

Br2 + 2e 2 Br- // Cl2 +2e 2 Cl

-

orHalf equation of oxidation

2 I- I2 + 2 e

Able to describe a chemical test to verify iodine

correctly

Sample answer

1. Pour (15) cm3 / a few drops of the displaced

halogen in a test tube

2. Add a few drops of starch solution3. Dark blue colour is formed

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(b)

(c)

Able to suggest metal M and metal N correctly

Sample answer

1. Metal M : copper // silver

2. Metal N : magnesium // aluminium // zinc

Able to explain the observation of the experiment

correctly

Sample answer

3. M is less electropositive than iron

4. Iron rust / oxidize to form Fe2+// iron atom loses

electron to form Fe2+ // Fe Fe2+ + 2e

5. Presence of Fe2+ ion produces blue spot

6. N is more electropositive than iron

7. N is oxidized // N atom lose electron to form N ion

8. Inhibits/Prevent iron from rusting

Able to draw the labell.ed diagram of rusting of iron

correctly

1. correct diagram

2. correct label [cathode, anode, water droplet, iron]Answer

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Oxygen


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Able to explain how the rusting of iron occurred

correctly

3. Iron atom lose electron /oxidized to form iron(II) ion

// Fe Fe2+ + 2e

4. Oxygen #and/ in water# gains electron / reduction to

form hydroxide ion, OH- //

O2 + 2 H2O + 4e 4 OH-

5. Iron(II) ion, Fe2+ and hydroxide ion, OH- combined to

form Iron(II) hydroxide //

Fe2+ + 2 OH- Fe(OH)2

6. Iron(II) hydroxide is oxidized to form hydrated

Iron(III) oxide as a rust.

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Total 20

paper 2 marking scheme 2013

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