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# Aqa chem 4/ chem 5 june 2016 thread watch

1. (Original post by Super199)
http://filestore.aqa.org.uk/subjects...5-QP-JAN13.PDF

3c.

why do you halve the oxygen value. I don't understand
Write out the equation of the reaction happening and you'll undertsand why. I've done it 2 ways here which gives the same answer:

2. (Original post by Bloom77)
Another oxidation question lol
I can't seem to do these simple ones 😭
Thank you!

Attachment 554477
NH3 has no charge so that's 0
SO4 has an oxidation state of -2
So X + 0 -2 = 0
Therefore, X = +2
So is that how you get the answer?

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Yeah ligands like NH3 and H2O are uncharged and it shows the overall is 0, hence just 2+ to counter the SO4(2-)
3. (Original post by SirRaza97)
Write out the equation of the reaction happening and you'll undertsand why. I've done it 2 ways here which gives the same answer:

See I tried writing out the equation, and I got the second one. I got the delta H as 89. But I don't get why you halve it, or in this cause you've doubled the temperature?
4. (Original post by Jmedi)
Yeah ligands like NH3 and H2O are uncharged and it shows the overall is 0, hence just 2+ to counter the SO4(2-)
THANK YOU

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5. what should I revise? Any predicitons
6. (Original post by emma_1111)
Is lattice dissociation always -ve?
Lattice dissociation: bonds are breaking: Bond breaking releases energy: It is always positive!!
7. (Original post by flylikeafly)
what should I revise? Any predicitons
if chem4 is representative, i would say absolutely anything could come up
8. (Original post by Super199)
See I tried writing out the equation, and I got the second one. I got the delta H as 89. But I don't get why you halve it, or in this cause you've doubled the temperature?
I haven't doubled the temp. I have doubled the enthalpy change. This is because in the second equation I am creating 2 lot's of water. So the energy required to create twice the amount will be twice the energy so deltaH is multiplied by 2.

In the first equation whichis how the mark scheme does it, is that you are creating 1 mol of water so deltaH is -242. The reason it's half of water because the first equation is 1/2O2 which means that the entropy must be half aswell.
9. (Original post by nutcase13)
if chem4 is representative, i would say absolutely anything could come up
yeah thats what I thought im just going over the book looking for sneaky things they could bring up but others seem to be discussing past paper questions
10. if it asks for strongest/reducing agent, how do you know whether to say its like Zn or Zn2+?
11. (Original post by jammypancake)
if it asks for strongest/reducing agent, how do you know whether to say its like Zn or Zn2+?
reducing agents are on the right hand side, and oxidising agents are on the left hand side
12. I will be so disappointed if chem 5 is like chem 4. I don't care if the paper is hard but it's the fact that a lot of revision will have been wasted
13. (Original post by flylikeafly)
yeah thats what I thought im just going over the book looking for sneaky things they could bring up but others seem to be discussing past paper questions
sneaky things meaning.....
sneaky things meaning.....
like asking us about things that I may have missed in the book or thought was never come up based on past papers.
15. (Original post by flylikeafly)
like asking us about things that I may have missed in the book or thought was never come up based on past papers.
I'm doing the same! If you find anything weird do you mind posting it here please?
16. http://filestore.aqa.org.uk/subjects...5-QP-JUN13.PDF
For 2cii) why do you times 0.0607 by 17.2?
17. (Original post by zombaldia)
Lattice dissociation: bonds are breaking: Bond breaking releases energy: It is always positive!!
hm im pretty sure bonds forming release energy and u have put in energy to break bonds so bonds breaking would take up energy
18. (Original post by SirRaza97)
I haven't doubled the temp. I have doubled the enthalpy change. This is because in the second equation I am creating 2 lot's of water. So the energy required to create twice the amount will be twice the energy so deltaH is multiplied by 2.

In the first equation whichis how the mark scheme does it, is that you are creating 1 mol of water so deltaH is -242. The reason it's half of water because the first equation is 1/2O2 which means that the entropy must be half aswell.
Safe.

Do you mind explain the strength of the Cl-Cl bond compared to a br-br bond?
19. (Original post by GO97)
hm im pretty sure bonds forming release energy and u have put in energy to break bonds so bonds breaking would take up energy
I agree with this.

Lattice enthalpy required bond forming between gaseous ions bond forming is negative

And hydration reauires bond forming with h2o which is also negative
20. what is formed when a solution containing Al3+ is reacted with excess OH-? [Al(OH)4]- or [Al(OH)6]3-

I've seen both

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