OCR 21st C C123 Unofficial Mark Scheme - Thursday 18th May 2017 Watch

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1. Calculate the % of methane (2 marks)
Calculated value of 27% (1)
Justification of value given (1) (eg 25% because other gases will be present)

2. Evolution of atmosphere (6 marks)
Carbon dioxide levels decreased because it formed fossil fuels, dissolved in oceans and was taken in by plants when they photosynthesised. Increases in recent times because we burn more fossil fuels.

Oxygen - green plants evolved and took in oxygen for photosynthesis so levels increased

Water - levels decreased as earth cooled down and steam condensed to form oceans.

3. Explain how carbon monoxide is formed (1 mark)
Incomplete combustion (1)

4. Explain how nitrogen monoxide is formed (2 marks)
Nitrogen and oxygen from the air (1)
React at high temperatures of the engine (1)

5. Explain why they both might be correct about reduction in pollution (3 marks)
Levels outside city decreased (1)
Levels inside decreased (1)
Decrease was greater inside than out (1)

6. Explain the trend of the graph (6 marks) Description:
- positive correlation
- As number of carbon atoms increases, boiling point increases
- Not proportional as it isn't a straight line going through the origin

- more carbon atoms means stronger intermolecular forces
- Stronger intermolecular forces means more energy is needed to break bonds
- More energy means a higher boiling point

7. Compare the different types of salt mining (6 marks)
- One produces impure salt whilst the other would produce pure salt
- Both can lead to damage to landscape eg subsidence
- Both requires fossil fuels - 1 in form of heat and one for the machinery ect

8. What elements in PVC (2 marks)
Carbon and hydrogen (1)
Chlorine (1)

9. Explain why plasticisers increase flexibility (3 marks)
Plasticisers push the chains apart (1)
So they can slide over each other (1)
So decreasing intermolecular forces (1)

10. Explain the issue of plasticisers (2 marks) Plasticisers could leach out of the product (1) Which could get into the food which we eat (1)

11. Identify the waste products from the equation (2 marks)
Calcium sulfide (1)
Carbon dioxide (1)

12. Identify a by product and say it's use (2 marks)
Chlorine (1)
It can kill microorganisms in water (1)

13. Explain how salt deposits are formed (2 marks)
Evaporation of ancient seas (1)
Sediments piled on top to bury it (1)

14. Explain why the salt deposits were found in Northern England (3 marks)

In Northern England, the salt deposits present underground formed under tropical conditions (1).
This was at a position near the equator (1)
and the movement of tectonic plates has moved this land to a location that is now Northern England (1)

15. Control variables for the shaft (3 marks)
Mass added (1)
Length of shaft (1)
Pressure of clamp (1)
It is done so that all results can be compared fairly (1)

2 factors and why for 3/3

16. Whose golf club is it likely to be? (3 marks) Calculating value (about 38 I think) (2) Therefore it's suited for a women (1)

17. Give a traditional use of alkali (1 mark) Making chemicals that bind to natural dyes (1) Ceramics (1)
Glass (1)
Paper (1)
Any correct answer

18. Circle the correct nano particle size (1 mark)
1nm-100nm (1)

19. Tick boxes about nano particles (3 marks) TTFF (3)

20. Explain why they may or may not use the new stitches from nanoparticles (3 marks)
Not much is known about them (1)
They know more about precious stitches (1) Could be dangerous (1)
Silver nano particles have antibacterial properties (1)
So they can reduce risk of infection (1)

21. Name another traditional source of alkali (1 mark)
Stale urine (1)

Missing about 4 marks worth of questions. Any help would be appreciated.

Thanks CandidateZero for helping fill in gaps.

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