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Aqa chem 4/ chem 5 june 2016 thread

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If you could send the paper I could give the answers in a day, I know people who can easily do the paper and get full marks.
Little stuck on something in the periodicity chapter.

If asked how would you explain the fact that silicon dioxide which is covalent has a higher melting point that sodium oxide but lower than magnesium and aluminium oxide?
Reply 23
Original post by cookiemonster15


Basically when you dissolve a solid into a solution like water etc etc etc... the disorder increases because you're going from a highly ordered solid to a more disordered liquid upon dissolving, therefore entropy change is positive so DS is negative remember the gibbs free energy equation if DS is positive its masked by the negative sign in the equation..

So T delta S is greater than Delta H


confusing stuff
Original post by cookiemonster15

I'm stuck on that question too :/
Revision is going fairly okay. I need an A in this. I was 9 UMS off an A last year :frown:. The only thing I have extreme trouble with is the god damn questions near the end of CHEM4 where they tell you a molecular formula and you have to draw two isomers of it. I suck at it and they are worth about 12 marks all together!!!
Original post by cookiemonster15


This is a bit tricky to understand but i'll try my best. So we are told that the enthalpy of solution of KCl is +17.2 KJ/ mol. The positive is important here as it shows it's endothermic so that means that the water will get colder here when it dissolves in it.

Q = mcT (mass x spc heat capacity x change in Temp)

What's Q? Well that will be our energy taken in (energy taken in because endothermic) when KCl dissolves in water. First work out the Moles of KCl > Mol = Mass/Mr = 5/74.6 = 0.067 mol

Our energy (Q) > Ethalpy of Solution x Mol = 17.2x10^3 x 0.067 = 1.153 kJ

A way to look at it, which might help you to understand, that if we multiply the units of Ethalpy of Solution by units of Mol we just get Joules which is energy ( KJ/ Mol x Mol = KJ). This is known as dimensional analysis. Not needed but helps kind of.

Using Q = mcT > 1.153x10^3 = 20 x 4.18 x T

Rearranging to get T we get T = 13.8 K

We stated that the temp of the water drops so final T is then 298 - 13.8 = 284.2 K

Hope that helps!
Original post by SirRaza97
Revision is going fairly okay. I need an A in this. I was 9 UMS off an A last year :frown:. The only thing I have extreme trouble with is the god damn questions near the end of CHEM4 where they tell you a molecular formula and you have to draw two isomers of it. I suck at it and they are worth about 12 marks all together!!!


Practise makes perfect.. I used to hate it so much but try practising again and again, you'll notice the techniques you pick up on when drawing the isomers..
Before you know it you'll be good at them hopefully ☺️
Original post by wednesday_adams
Hi everyone!

I thought I'd start a thread where we can all discuss the upcoming AQA chemistry exams this june!

Feel free to post here any questions or revision tips here

How is revision going? Or not going? :smile:

Dates:
Chem 4: June 14 2016
Chem 5: June 22 2016


Thanks for making this thread OP! I've added it to the A Level Exam Directory which can be found here. If I've missed any, or you want to make more exam thread, just give me a tag in the relevant thread and I'll add it in there. Best of luck in your exams! :clap2::clap2::clap2:
Reply 29
Done a lot of chem 4 revision, not so much chem 5 but that'll be my main aim for the next month or so, especially memorising all the colours of the ions at the end!
how many papers have you guys done?
Hi everyone,

I need to remind you that it isn't okay to discuss ISA and EMPA exams on TSR. You can read the announcements have at the top of every forum here. These exams are taken at different times by different people and discussing answers give others an unfair advantage.

Reply 33
im just planning on learning collins book extensively, did it last year and it worked :-)
2015 papers are out!!!!!:surprise:
Why is it that propan-2-ol can't have a concentration? This question is related to last year's empa.

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Can someone help me withe questions like these please?
Is there a method to figuring out the right equation? The ones in the book i can memorise and just write down when asked but these two I actually have to work out and write but I keep getting them wrong.

If someone has a good way of working out the equations please let me know.

http://filestore.aqa.org.uk/subjects/AQA-CHEM5-QP-JUN12.PDF Q8b

http://filestore.aqa.org.uk/subjects/AQA-CHEM5-QP-JUN13.PDF Q8a
Reply 37
can someone help me with this question jan 2010

A chemical company has a waste tank of volume 25 000 dm3. The tank is full ofphosphoric acid (H3PO4) solution formed by adding some unwanted phosphorus(V)oxide to water in the tank.A 25.0 cm3 sample of this solution required 21.2 cm3 of 0.500 mol dm–3 sodiumhydroxide solution for complete reaction.Calculate the mass, in kg, of phosphorus(V) oxide that must have been added to thewater in the waste tank.

i worked out the moles of NaOH which was 0.0109

and then using the equation P4O10+ 6H20> 4H3PO4 i thought wouldve given me the moles of P4O10 when divided by 4 but it says 0.0109/3 even with the reaction H3PO4+ 12NaOH> 4h3po4 it would be wrong have i got the formula wrong?
Original post by shiney101
Can someone help me withe questions like these please?
Is there a method to figuring out the right equation? The ones in the book i can memorise and just write down when asked but these two I actually have to work out and write but I keep getting them wrong.

If someone has a good way of working out the equations please let me know.

http://filestore.aqa.org.uk/subjects/AQA-CHEM5-QP-JUN12.PDF Q8b

http://filestore.aqa.org.uk/subjects/AQA-CHEM5-QP-JUN13.PDF Q8a


I believe you're supposed to use what you know about V2O5 catalysts, the equations are kind of similar if you look at the changes in oxidation states. I got this right a few weeks ago but it defo took a lot of effort lol
Can someone help me with q9? It's about percentage error, and they've said in the answer that the titre will be 24.4 so you can use that.
I've forgotten what the formulae for percentage error is ://
http://filestore.aqa.org.uk/subjects...T-P10-TEST.PDF

Thanks

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