Edexcel A2 Chemistry Exams -6CH04 (14th June) and 6CH05 (22nd June) Discussion Thread

Reply 1440

Don Pedro K.

9

Original post by MacroniCheese

Good stuff! You should be good to go by next Wednesday :smile:

Looool I hope so XD Won't stop me from worrying myself like crazy though hahaha :smile:

Reply 1441

lordoftheties

13

Hey guys, anybody got any tips on EXAM TECHNIQUE?? Im so sussed by it, I just cant seem to hack that understanding of what it is and how to master it :frown:

whelp.

Reply 1442

Don Pedro K.

9

@samb1234 @Ayman! Can someone explain why the reaction on the right occurs by addition?

Reply 1443

keres

2

Original post by keres

15 cm3 of a gaseous hydrocarbon requires 90 cm3 of oxygen for completecombustion, both volumes being measured at 15􀁱C and 1 atm. The formula of thehydrocarbon is

A C4H6
B C4H8
C C4H10
D impossible to calculate without knowing the molar volume of gases underthese conditions.

Guys how do you do this? Please help

Original post by keres

15 cm3 of a gaseous hydrocarbon requires 90 cm3 of oxygen for completecombustion, both volumes being measured at 15􀁱C and 1 atm. The formula of thehydrocarbon is

A C4H6
B C4H8
C C4H10
D impossible to calculate without knowing the molar volume of gases underthese conditions.

Guys how do you do this? Please help

Anyone? :') x

Reply 1444

keres

2

Original post by Don Pedro K.

@samb1234 @Ayman! Can someone explain why the reaction on the right occurs by addition?

It's because benzene needs to undergo substitution reactions because the delocalised ring of electrons needs to be maintained for stability - however with cyclohexa1-3 diene, there is no delocalised ring structure. it is comprised of 3 double bonds, and double bonds can undergo addition reactions.

Reply 1445

Don Pedro K.

9

Original post by keres

It's because benzene needs to undergo substitution reactions because the delocalised ring of electrons needs to be maintained for stability - however with cyclohexa1-3 diene, there is no delocalised ring structure. it is comprised of 3 double bonds, and double bonds can undergo addition reactions.

Ahhh of course! Thank you :smile:

!

Reply 1446

sabahshahed294

12

Original post by keres

Anyone? :' :wink:

x

What's the answer for this?

Reply 1447

keres

2

Original post by sabahshahed294

What's the answer for this?

B x

Reply 1448

sabahshahed294

12

Original post by keres

B x

I did it like this:-
We have the volume of the hydrocarbon and oxygen given to us(gaseous volumes) so I used the equation, moles=volume/molar volume and found the moles of both the hydrocarbon and oxygen which had a ratio of 1:6. As this is a complete combustion, we know the products are gonna be Carbon Dioxide and Water. So, I just wrote the equation using the molar ratio I calculated:-

CxHy + 6O2----> 4CO2+4H20.

There are total 12 oxygen atoms so to balance them, I wrote 4 CO2 and 4H20.
This means that carbon:hydrogen ratio is 1:2 hence 4:8 in this case which is why you get C4H8 as the answer(B)

Reply 1449

setarcoppiH

Original post by MacroniCheese

Good stuff! You should be good to go by next Wednesday :smile:

You know you're on TSR when 'good to go' = 120 ums. xD

Reply 1450

Ayman!

15

Original post by Don Pedro K.

@samb1234 @Ayman! Can someone explain why the reaction on the right occurs by addition?

It's an alkene

Reply 1451

Science&Despair

1

Anyone know if anyone got anywhere with putting together an unofficial mark scheme?

Reply 1452

gabby07

11

Hey - what compound do diazonium ions decompose to when heated above 10^oC? Was on a past paper but I've forgotten!

Reply 1453

samb1234

OP

13

Original post by gabby07

Hey - what compound do diazonium ions decompose to when heated above 10^oC? Was on a past paper but I've forgotten!

phenol

Reply 1454

Don Pedro K.

9

Original post by samb1234

phenol

Have you tried June 2013 (R)?

Reply 1455

samb1234

OP

13

Original post by Don Pedro K.

Have you tried June 2013 (R)?

not yet only done june 2013 so far

Reply 1456

Don Pedro K.

9

Original post by samb1234

not yet only done june 2013 so far

Okay haha

Reply 1457

Peppercrunch

14

How come the answer is C here? I thought it'd be A as the electrodes are the same metals as those in solution?

Reply 1458

C0balt

16

Original post by Peppercrunch

How come the answer is C here? I thought it'd be A as the electrodes are the same metals as those in solution?

if you put iron you'd set up potential of Fe/Fe2+ and Fe/Fe3+

Reply 1459

Don Pedro K.

9

Original post by Peppercrunch

How come the answer is C here? I thought it'd be A as the electrodes are the same metals as those in solution?

If you look at the beaker on the right, you can see that the solution contains a mixture of FeSO4 (Fe2+ ions) and Fe2(SO4)3 (Fe3+) ions. Hence, there is no metal iron involved. The electrode is therefore made out of platinum, which is kind of the convention.

Edexcel A2 Chemistry Exams -6CH04 (14th June) and 6CH05 (22nd June) Discussion Thread

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