CHEMISTRY answers

Section I

Part A

1. B

2. A

3. A

4. C

5. B

6. B

7. D

8. C

9. D

10. B

11. C

12. B

13. D

14. B

15. B

16. A

17. B

18. C

19. C

20. A

PART B

Question Part Answer Marks

21 (a) (i)

1

(a) (ii) Phenylethene 1

(b) Names ONE structural property:

Irregularly shaped, not packed together very tightly

Large molecule, higher dispersion forces, stronger polymer bonds Names ONE physical property:

Light

Easily shaped

Low density Names ONE use:

Styrofoam cups

Sound proofing

Surfboard core

1 1 1

22 (a) (i) K2O, CaO 1

(a) (ii) SO2, N2O5 1

(b) Writes ONE of these: K2O(s) + H2O(l) 2KOH(aq) CaO(s) + H2O(l) Ca(OH)2 (aq) SO2(g) + H2O(l) H2SO3(aq) N2O5(g) + H2O(l) 2HNO3(aq)

1

(c) Can act as both an acid and a base 1

23 Identifies the production of polyethylene as an addition reaction and the production of cellulose as a condensation reaction. 1

Defines addition reaction as the opening of the double bond to allow monomers to attach. Defines condensation reaction as the formation of a new bond which involves the elimination of water. Writes addition reaction equation. For example,

Writes condensation reaction equation. For example,

1 1 1

24 (a) Identifies ONE catchment area e.g. Warragamba dam 1

(b) Identifies ONE of the following contaminants:

Heavy metal poisoning: o Lead Pb2+ o Mercury Hg o Cadmium Cd o Silver Ag+

Eutrophication o Cyanobacteria o Phosphates o Nitrates o Ammonia

Hard water o Calcium Ca2+

1

o Magnesium Mg2+ Outlines chemical test:

Test for heavy metals: o Atomic Absorption Spectroscopy (AAS)

A solution of the sample is sprayed into a flame to create a vapour of atoms while a light beam is passed through the flame, the light is analysed by a detector, the results are used to construct a calibration curve

o Precipitation test: Test for Pb2+: Add Cl- to form white precipitate, or add I- to form yellow precipitate Test for Ag+: Add Cl- to form white precipitate

Test for eutrophication: o Colorimetric test:

Nitrates and phosphates are converted to coloured compounds using standard reagents, the depth of colour is measured, converted to concentration units

o Test for Turbidity: Pour water into turbidity tube, measure the depth of water at which the black lines disappear

o Test for Dissolved Oxygen (DO) and Biochemical Oxygen Demand (BOD): Use data loggers and oxygen probe

Test for hard water: o Lather with soap

2 marks for ONE of these points

(c) Identifies each of the steps and describes each step:

Monitoring the catchment area o Ensure that the catchment area is clean e.g. ban any agricultural practices, remove dead animals

Screening o Pass water through metal screens to remove large debris such as sticks, leaves, trash

Aeration o Add oxygen to the water

Flocculation o Tiny suspended particles are coagulated together

Sedimentation o Particles are allowed to settle to the bottom of large tanks and are removed

Filtration o The water is passed through a bed of fine sand and gravel

pH adjustment

½ mark for each step

o Adjusting the pH to close to 7

Chlorination o Chlorine gas is pumped through the water to disinfect the water

25 Identifies that cellulose can be converted to ethanol Outlines advantages of ethanol:

Comes from a renewable resource

Reduces greenhouse gas emissions because it is carbon neutral (the CO2 produced is the same that is used up in photosynthesis)

Ethanol burns more cleanly o C2H5OH(l) + 3O2(g) 2CO2(g) + 2H2O(g)

Outlines disadvantages of ethanol:

Large resource allocation to agricultural land

Waste disposal presents major environmental problems

Ethanol has a lower heat of combustion than petrol, hence would need to re-fuel more often

Large amount of energy used in the production of ethanol from cellulose

Only 10% can be safely added to petrol, more than that will require modification of engines, which is costly and a hassle Assesses the viability of ethanol:

Ethanol has potential to be a petrol additive, but the costs outweigh the benefits, hence it is not economically viable at the moment

1 1 1 1 1 mark for flow of arguments, and assessment makes sense based on

what arguments were presented

26 Identifies ONE pair of conjugate acid/base:

H2CO3 /HCO3-

Explains how it maintains the pH:

When H+ is added to the system, the equation shifts to the right, to maintain the equilibrium

When H2O is added to the system, the equation shifts to the left, to maintain the equilibrium

Le Chatelier’s principle Uses the equations:

H+(aq) + HCO3

-(aq) ⇌ H2CO3 (aq)

H2CO3 (aq) ⇌ H2O(l) + CO2(g)

1 1 1 mark each

27 Identifies ONE example (i.e. one alcohol and one alkanoic acid to make one ester):

Ethanol and butanoic acid makes ethyl butanoate Identifies ALL the conditions:

Around 40°C

Presence of yeast

Presence of water

Presence of sulfuric acid

Anaerobic conditions Outlines the procedure with correct use and set-up of equipment:

1 1 2

28 Briefly explains Atomic Absorption Spectroscopy Outlines the advantages of AAS on society Outlines the advantages on the environment Outlines the disadvantages on society Outlines the disadvantages on the environment Assesses the overall impact

1

33 (b) (i)

2

(ii)

(c) (i)

(ii)

(d)

(e)

34 (a)

(B)

(C)

(D)

(e) (i)

1

(e) (ii)

35 (a)

(b)

(c)

(d)

37 (a) (i)

(a) (ii)

(b)

(c)

(d)

(e) (i)

(e) (ii)