AQA CHEM5 A2 Chemistry - 19th June 2013

Scroll to see replies

Reply 1160

DELETED ACCOUNT

3 exams left. I can almost taste the freedom. We can do this.

Reply 1161

AmyLH

Original post by alongcamelucy

How is everyone learning all the transition metal colours / substitution reactions etc? Any tips?

I'm just staring at a piece of paper with them all on and hoping they go in.

I'm trying to make little things to help me like
Copper is mostly blue
Fe2+ is always green
CoCO3 it's like CoCO chanel, which is girly so pink
For Co3+ it's brown/dark brown
For all of Cr3+ it's green except for NH3 which is purple. Idk why but I always think NH3 sounds posh and like purple is a regal colour. Idek why :tongue:

Cr6+ is orange/yellow and like in the map I've drawn they're at the top like the sun, then Cr2+ is at the bottom which is blue like the sea

After typing this out I have realised how ****ing weird I am :tongue:

Reply 1162

sacheeen

Original post by Beth_L_G

http://m.youtube.com/watch?v=EbzqKn34kKk

Thank you!

Reply 1163

poopnoddy

Hey guys pretty confused on 7bii of the jan 11 paper, were told h202 is reduced to OH- ions, therefore the cr3+ ions have been oxidised to cr+6 but i dont understand how you find the 2nd half equation, is it because you balance the 3e-s on the right first to deal with the oxidation state change then balance the charges by adding OH- to the left then the h2o's on the right?

Posted from TSR Mobile

ImageUploadedByStudent Room1371242197.348628.jpg21.8KB

Reply 1164

crc290

Original post by poopnoddy

Not sure which half equation you're on about, but I'd just do it like this

H₂O₂ + 2e^-

\rightarrow

2OH^-
[Cr(OH)₆]^3-

\rightarrow

CrO₄^2- + 2H₂O + 2H⁺ + 3e^-

Then combine them:
2[Cr(OH)₆]^3- + 3H₂O₂

\rightarrow

2CrO₄^2- + 4H₂O + 4H⁺ + 6OH^-

The four H⁺ ions combine with four of the OH^- ions, meaning the equation can be simplified to:
2[Cr(OH)₆]^3- + 3H₂O₂

\rightarrow

2CrO₄^2- + 8H₂O + 2OH^-

Reply 1165

darkred

I keep reading Cu/Co/Cr wrong in practice questions and getting them mixed up. Time to call it a day with revision I think.

Reply 1166

loknath

You know for the june 2012 calculation...I'm getting more than 100%
I'm going to cry
K bye

Reply 1167

darkred

Original post by loknath

You know for the june 2012 calculation...I'm getting more than 100%
I'm going to cry
K bye

I think the answer is right though, it was an examiner's cockup. Or something like that. Either way a lot of people were WTFing at that last year.

Reply 1168

crc290

Original post by loknath

You know for the june 2012 calculation...I'm getting more than 100%
I'm going to cry
K bye

Your ratio from part i is probably wrong. The mark scheme says a ratio of 3:7 or 2:5 can give an answer of more than 100%. You still get full marks for part ii though because its error carried forward :smile:

Reply 1169

crc290

Original post by failingatm

I think the answer is right though, it was an examiner's cockup. Or something like that. Either way a lot of people were WTFing at that last year.

No the right answer was 93.4% but they do accept loads of different answers so you could be right about some sort of cockup :confused:

Reply 1170

darkred

Original post by crc290

No the right answer was 93.4% but they do accept loads of different answers so you could be right about some sort of cockup :confused:

Ahh right. Well I just remember people coming out of the exam all going on about the answer being more than 100%

I know last years paper wasnt very popular after the exam

Reply 1171

crc290

Original post by failingatm

Ahh right. Well I just remember people coming out of the exam all going on about the answer being more than 100%

I know last years paper wasnt very popular after the exam

It was a weird question. I've never seen one on any other past paper where you have to combine 3 half equations, so I guess the examiners were giving people the benefit of the doubt

Reply 1172

loknath

Original post by crc290

It was a weird question. I've never seen one on any other past paper where you have to combine 3 half equations, so I guess the examiners were giving people the benefit of the doubt

I HAD A 2:5 RATIO
NO JOKE THIS IS THE HAPPIEST IVE BEEN ALL DAY
high on coffee sorry
I think I just ate dog treat no it was a chocolate button
I'm going mental. Dayum.

Reply 1173

crc290

Original post by loknath

I HAD A 2:5 RATIO
NO JOKE THIS IS THE HAPPIEST IVE BEEN ALL DAY
high on coffee sorry
I think I just ate dog treat no it was a chocolate button
I'm going mental. Dayum.

Well I bet you're glad you'd only lose 1 mark and not 6

The actual ratio is 3:5 though...

Reply 1174

Chris-69

Original post by crc290

Well I bet you're glad you'd only lose 1 mark and not 6

The actual ratio is 3:5 though...

I'm confused? What's with the 2:5 thing? Is it do do with carry over marks? I.E you only lose the accuracy mark? Because I don't see where the cock-up is :s-smilie:

Reply 1175

cheesypuff

Original post by frogs r everywhere

3 exams left. I can almost taste the freedom. We can do this.

what exams have you done already and how did they go?

Reply 1176

igobyursula

Original post by loknath

You know for the june 2012 calculation...I'm getting more than 100%
I'm going to cry
K bye

Aqa made an error on that paper. Do not use the mole ratio they provide. It's 3:5, not 3:7.

Reply 1177

A sheesh

Anyone else struggling to focus on chem with bio coming up?

Reply 1178

igobyursula

Original post by Chris-69

I'm confused? What's with the 2:5 thing? Is it do do with carry over marks? I.E you only lose the accuracy mark? Because I don't see where the cock-up is :s-smilie:

Aqa cocked up. They provided an incorrect mole ratio. Cause they are so clever they did not bother to check.

Reply 1179

Zytex

Original post by SexyAndIKnowIt.

Do we have to know about silver/ silver chloride, calomel, zinc/ carbon and lithium ion electrodes or do we just have to know them as examples of whatever.
If so - what are they all used for,, don't know anything on the above 4 electrodes so if we have to know anything about them, I would appreciate some guidance thanks x