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# 2016 IGCSE Chemistry Paper 2 Unofficial Mark Scheme 2016 Watch

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1. (Original post by Nurne)
C8H18 +8 1/2O2 -> 8CO2 + 9H20

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was that after the isomer questions?
2. For the dot and cross diagram did u have to put 8 or 0 electrons on magnesium
3. (Original post by igggy)
For the dot and cross diagram did u have to put 8 or 0 electrons on magnesium
im pretty sure its 8 because its an ion, it has lost its 2 outer electrons to form the outer shell and formed a shell with 8 electrons.
4. Question 3 (?) 22.60, 22.45, 22.55 for the concordant results (numbers might be wrong, but they were boxes 2, 3 and 4)
Add them up and divide by theee for average 22.53 (I think that was the average, cant be bothered to check)
5. (Original post by rcmack)
was that after the isomer questions?
Yup..

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6. (Original post by Abodee1)
im pretty sure its 8 because its an ion, it has lost its 2 outer electrons to form the outer shell and formed a shell with 8 electrons.
Ok good thats what i did phew
7. For 4d I got CH3-CH2-CH2-CH2OH
And 4e) -(-CH2-CHX-)-
There was another molecule where the X is, but I cant remember its formula
8. For the question about the equation for incomplete combustion was the answer
C8H18 + 6O2 > 6C + CO2 + CO + 9H2O
9. You need to add an extra ch2 to 4d. It was butanol not propanol.

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10. (Original post by Nurne)
C8H18 +8 1/2O2 -> 8CO2 + 9H20

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It wasn't 8CO2 it was 8CO since incomplete combustion causes Carbon Monoxide to form instead of Carbon Dioxide, due to the lack of Oxygen.
11. Also there was a question about drawing the polymerisation of an alkene? What do you draw?
12. (Original post by Debby 123)
It wasn't 8CO2 it was 8CO since incomplete combustion causes Carbon Monoxide to form instead of Carbon Dioxide, due to the lack of Oxygen.
Sorry i meant 8CO carbon monoxide.

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13. The isomer of but-1-ene was but-2-ene.
14. (Original post by rcmack)
yea same, do you remember what question number that was?
sorry, i dont
15. Yeah but I thought incomplete combustion causes some carbon monoxide and carbon to form, but also some water and carbon dioxide?
16. (Original post by iah1700)
For the question about the equation for incomplete combustion was the answer
C8H18 + 6O2 > 6C + CO2 + CO + 9H2O
I got C8H18 + 8.5O2 -> 8CO + 9H20 (my friends agreed but we could be wrong)
I think yours might also be correct, as it's the example given in the CGP revision guide, although I don't think it said anything about producing carbon in the question.
17. It is red. It said AFTER it has been neutralised
18. (Original post by Ashnii34)
For the aluminium question was it 180g or 540g?
I got 180g but some people say it's 540g
I got 180g. 20 F of electricity = 3 moles of electrons. 3 moles of electrons: 1 mole of aluminium (from half equation given). 20/3 moles of aluminium made. Mass = moles × Mr = 20/3 x 27 = 180 g
19. (Original post by Ashnii34)
For the aluminium question was it 180g or 540g?
I got 180g but some people say it's 540g
Defo 180

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20. (Original post by Ashnii34)
After it has been neautralised means it's neutral so it's orange
Common misconception, it turns acidic

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