AQA CHEM4 and CHEM5 revision thread 2016

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theboss1998

Chemistry unit 5
January 2010
Question 3h
Is it okay yo say:
Electrolysis of water to obtain hydrogen uses fossil fuels so not carbon neutral

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That seems ok to me and it sounds right.

Reply 81

ahsan_ijaz

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Can anyone explain why I got this wrong ? I don't understand ! It's a bit confusing - I got 2/4 but I clearly got the step wrong and I'm
Struggling to understand the mark scheme

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Reply 82

ahsan_ijaz

Ok sorry I managed to take a picture of the wrong stuff

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Reply 83

ManOfJustTin

Original post by ahsan_ijaz

I think you forgot to divide your excess moles of OH by the volume to get the concentration to use in your equation.

(edited 7 years ago)

Reply 84

Engineerrookie

Is Platinum the only transition metal that can a square planar shape or is it Nickel as well???

Reply 85

Superbubbles

does anyone know why in the condensation reaction 2n-1 water is produced

Reply 86

Splashoid

Original post by Engineerrookie

Is Platinum the only transition metal that can a square planar shape or is it Nickel as well???

The shape of the molecule will depend on the molecule itself. I don't think there are any rules as to which elements can form certain shapes.

Reply 87

Engineerrookie

Original post by Superbubbles

does anyone know why in the condensation reaction 2n-1 water is produced

What do you mean?

Reply 88

High Stakes

Feel ready for CHEM4. But CHEM5 I've neglected lol.

Reply 89

badaman

Original post by High Stakes

Feel ready for CHEM4. But CHEM5 I've neglected lol.

Chem 4 can have awkward Q.s

Reply 90

ajsullivan

Original post by Splashoid

The shape of the molecule will depend on the molecule itself. I don't think there are any rules as to which elements can form certain shapes.

Actually, while there are no rules, there is one other compound that you need to know in regards to square planar geometry: tetracyano nickelate (II). That is a nickel 2+ ion surrounded by four CN- ligands (hence the overall negative two charge).

So this and Cisplatin are the two you should know off the top of your head.

Good luck!

Alex

Reply 91

thenextchemist

Can someone please explain this part of the golby notes,
I don't understand it tbh
Baby words please lol :smile:

Thank you!
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Reply 92

Superbubbles

Original post by Engineerrookie

What do you mean?

dont worry i understand it now thanks anyways i was asking why 2n-1 water molecules are produced in polymerisation but this is because the end of the chain still has OH nd O hence the -1

Reply 93

Superbubbles

why is kc only affected by temperature?

Reply 94

SirRaza97

Original post by Superbubbles

why is kc only affected by temperature?

Changing the temperature effects the rate at which the fowards reaction and the backwards reaction happen. So when the equilibrium shifts to oppose the change in temp, you are also changing the rate at which each reaction is happening thus changing the value of Kc to satisfy the new system.