YEAR 11 CHEMISTRY MARKING SCHEME

[Pages:6]DEPARTMENT FOR CURRICULUM, LIFELONG LEARNING AND EMPLOYABILITY Directorate for Learning and Assessment Programmes Educational Assessment Unit

Annual Examinations for Secondary Schools 2021

Track 3

YEAR 11

CHEMISTRY

MARKING SCHEME

Item 1a i

ii

Answers and guidelines Section A

An element is a chemical substance that is made of only one type of atom. Isotopes are atoms of the same element that have the same number of protons but different number of neutrons. Accept: Isotopes have the same atomic number but different atomic mass.

1 mark for electronic configuration. 1 mark for number of protons and neutrons.

Marks 1 1

b

2

c d 2 a b c d

3 a

The mass of chlorine-35 is: 35 ? 75 = 2625 The mass of chlorine-37 is: 37 ? 25 = 925 Total mass is : 3550 Average mass of chlorine is: 3550 /100 = 35.5 Cl2

1

1 Total 6

Transition metals.

1

The atomic size increases since going down a group, elements have

increasing numbers of shells.

2

Going across period 3, the valency increases from group 1 (valency = 1)

to group 4 (valency = 4) and then decreases from group 4 to group 8

2

(valency = 0).

Elements which show both metallic and non-metallic characteristics.

1

Total 6

1 mark for electron configuration of the sodium ion.

1 mark for electron configuration of the chloride ion. 3

1 mark for charges on ions enclosed in square brackets.

Chemistry ? Marking Scheme ? Year 11 ? Track 3 ? 2021

Page 1 of 6

Item 3 b

Answers and guidelines 1 mark for electron configuration of oxygen.

1 mark for electron configuration of hydrogen. 1 mark for correct sharing of electrons.

Marks 3

Total 6

4 a b c d

2Pb(NO3)2 2PbO + 4NO2 + O2

1 mark for formulae. 2

1 mark for balancing.

It needs to be performed in a fume cupboard.

1

2NO2 + H2O HNO2 + HNO3

1 mark for formulae. 2

1 mark for balancing.

Any one of: causes acid rain, respiratory problems or causes limestone 1

building corrosion.

Total 6

5 a b c d

A base is a metal oxide or hydroxide which may be soluble or insoluble in 1

water, whereas an alkali is a soluble base.

Base: copper(II) oxide.

Alkali: sodium hydroxide.

2

Accept chemical formulae.

Any one of: corrosive, low pH, sour. Accept other reasonable answers.

1

NaOH + H2SO4 NaHSO4 + H2O

1 mark for formulae. 2

1 mark for balancing.

Total 6

6 a

Any one of: relatively high densities, variable valencies, form coloured compounds.

1

b i Iron(II) chloride or FeCl2

1

ii Iron(III) chloride or FeCl3

1

c

It oxidises to form iron(III) chloride. OR

1

From green it turns brown.

On adding drops of sodium hydroxide until in excess to both compounds,

iron(II) chloride forms a green precipitate while

1

d

the iron(III) chloride forms a brown precipitate.

1

Both precipitates are insoluble in excess sodium hydroxide solution.

Total 6

Page 2 of 6

Chemistry ? Marking Scheme ? Year 11 ? Track 3 ? 2021

Item 7 a

Answers and guidelines

Marks

Accept correct variations of this

diagram.

1 mark for diagram. 1 mark for labelling.

2

b i Hydrogen. ii Chlorine. 2Cl- Cl2 + 2e-

c

1 1

1 mark for formulae. 2 1 mark for balancing.

Total 6

8 a b

c

Copper(II) chloride, CuCl2 Calcium carbonate, CaCO3 Cu2+ + 2OH- Cu(OH)2

2 2

1 mark for formulae. 2 1 mark for balancing.

Total 6

9 a b c

Natural gas is a mixture of gaseous hydrocarbons (mainly methane) while

crude oil is a mixture of hydrocarbons that include both gaseous and liquid 1

components.

Fractional distillation.

1

1. Crude oil is heated and enters at the bottom of a fractionating tower.

2. The hot gases rise up a fractionating tower.

3. Hydrocarbons of different molecular mass are condensed at different

3

parts of the fractionating tower depending on their boiling point.

d i

1

ii

iii

e

CnH2n-2

Chemistry ? Marking Scheme ? Year 11 ? Track 3 ? 2021

1 1 1

Page 3 of 6

Item 9 f

g i

ii

Answers and guidelines

Pentane.

CH2BrCH2Br

Accept displayed formula.

Do not accept molecular formula.

Reddish brown colour of bromine decolourised quickly.

Total

Marks 1

1

1 12

SECTION B

Method:

2 beakers were filled with copper(II) nitrate solution, 2 beakers were filled

with iron(III) nitrate solution while another 2 beakers were filled with

magnesium nitrate solution. A magnesium and an iron strip were placed in

beakers filled with copper(II) nitrate. A magnesium and a copper strip were

placed in beakers filled with iron(III) nitrate while a copper and an iron

strip were placed in beakers filled with magnesium nitrate.

3

Results:

copper(II) nitrate iron(III) nitrate magnesium nitrate

Copper

1

Iron

1

10 a

Magnesium

1

Equations:

Fe + Cu2+ Fe2+ + Cu

2

Mg + Cu2+ Mg2+ + Cu

2

3Mg + 2Fe3+ 3Mg2+ + 2Fe

2

1 mark each for formulae

1 mark each for balancing.

Conclusion:

This goes to show that magnesium is more reactive than iron and copper

since it displaced them both from their solutions, while iron is more

reactive than copper since it displaced it from its solution.

1

Therefore, the order of decreasing reactivity is magnesium, iron, copper.

1

2Fe2+ + 2e 2Fe3+ b i

1 mark for formulae. 2

1 mark for balancing.

ii Chlorine gas is the oxidising agent because it is gaining electrons.

2

iii Iron in iron(II) chloride (Fe2+) is the reducing agent since its oxidation

2

number increases.

Total 20

Page 4 of 6

Chemistry ? Marking Scheme ? Year 11 ? Track 3 ? 2021

Item

Answers and guidelines

Sulfur is burned in air to produce sulfur dioxide.

S + O2 SO2

Marks 1 2

11 a

Sulfur dioxide is then reacted with oxygen gas

1

in the presence of vanadium pentoxide which acts as a catalyst

1

and at a pressure of about 2 atmospheres.

1

2SO2 + O2 2SO3

2

Sulfur trioxide is reacted with sulfuric acid to produce oleum.

1

This step is taken since the reaction of sulfur trioxide with water is a highly

exothermic reaction.

1

SO3 + H2SO4 H2S2O7

2

Oleum is then reacted with water to produce concentrated sulfuric acid.

1

H2S2O7 + H2O 2H2SO4

2

b i An increase in pressure would favour the production of sulfur trioxide.

1

ii A decrease in the surface area of the catalyst would increase the time it

1

takes for the system to reach equilibrium.

2NH4OH(aq) + H2SO4(aq) (NH4)2SO4(aq) + 2H2O(l)

1 mark for formulae.

c

3

1 mark for balancing.

1 mark for state symbols.

Total

20

12 a b

1. Pour an amount of dilute hydrochloric acid into a conical flask. 2. Place the conical flask filled with acid, an excess of calcium carbonate

chips and a glass wool on a digital weighing balance to determine the initial mass. 3. As the stopwatch is switched on, the calcium carbonate chips are

5 transferred to the conical flask so that the reaction starts. 4. This is followed by placing the glass wool at the neck of the conical flask to avoid acid from escaping the flask. 5. The mass of the whole setup is recorded every minute until three readings have the same value.

1 mark for equipment. 1 mark for setup. 1 mark for labels.

3

Chemistry ? Marking Scheme ? Year 11 ? Track 3 ? 2021

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Item

Answers and guidelines

Marks

12 c

5

1 mark for title of graph. 1 mark for axes labels.

1 mark for points plotted. 1 mark for smooth curve. 1 mark for graph occupying at least 75% of the graph paper.

d

3

1 mark for sketch starting at 102.8 g and 0 minutes.

1 mark for sketch below the graph plotted in part c).

1 mark for sketch ending at 99.0 grams and 7 minutes.

e

At the seventh minute.

1

CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2O(l) + CO2(g)

f

1 mark for formulae. 3

1 mark for balancing.

1 mark for state symbols.

Total 20

Page 6 of 6

Chemistry ? Marking Scheme ? Year 11 ? Track 3 ? 2021

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