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2016 IGCSE Chemistry Paper 2 Unofficial Mark Scheme 2016

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Reply 40

rcmack

Original post by Nurne

C8H18 +8 1/2O2 -> 8CO2 + 9H20

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was that after the isomer questions?

Reply 41

igggy

For the dot and cross diagram did u have to put 8 or 0 electrons on magnesium

Reply 42

Abodee1

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.

Reply 43

Lelanor

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)

Reply 44

Nurne

Original post by rcmack

was that after the isomer questions?

Yup..

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Reply 45

igggy

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

Reply 46

Lelanor

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

Reply 47

username2582349

For the question about the equation for incomplete combustion was the answer
C8H18 + 6O2 > 6C + CO2 + CO + 9H2O

Reply 48

Nurne

You need to add an extra ch2 to 4d. It was butanol not propanol.

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Reply 49

Debby 123

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.

Reply 50

username2582349

Also there was a question about drawing the polymerisation of an alkene? What do you draw?

Reply 51

Nurne

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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Reply 52

Abodee1

The isomer of but-1-ene was but-2-ene.

Reply 53

Abodee1

Original post by rcmack

yea same, do you remember what question number that was?

sorry, i dont :frown:

Reply 54

username2582349

Yeah but I thought incomplete combustion causes some carbon monoxide and carbon to form, but also some water and carbon dioxide?

Reply 55

Lelanor

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.

(edited 7 years ago)

Reply 56

dec1153

It is red. It said AFTER it has been neutralised

Reply 57

Lelanor

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