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AQA CHEM5 A2 Chemistry - 19th June 2013

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thankyouuuuuu
Could someone please answer a few questions I have about the specimen paper:
1. 2c(ii) says that 'Four moles gaseous reactant forming' but isn't it three?
2. 3b(i) - I don't understand how this question has been done
3. 3b9ii0 - Cell e.m.f is 0.06 V but I got 0.60V (0.77-0.17) - I don't understand how it's 0.06V

http://filestore.aqa.org.uk/subjects/AQA-CHEM5-W-SQP-07.PDF
http://filestore.aqa.org.uk/subjects/AQA-CHEM5-W-SMS-07.PDF
do we need to know the ideal gas equation and when doing calculations, do you use the whole numbers to calculate, but write out your answers to 3 sig figures at each step?
Could someone please explain why the answer is I.E. = (+)1451 (kJ mol-1) to 1(b) on the June 2007 paper. I don't understand why and how it is this answer.

Thanks

http://www.a-levelchemistry.co.uk/AQA%20A2%20Chemistry/Unit%205/Unit%205%20Past%20Papers%20and%20Revision%20Aids/past%20papers/Unit%205%20June%202007%20ms.pdf
http://www.a-levelchemistry.co.uk/AQA%20A2%20Chemistry/Unit%205/Unit%205%20Past%20Papers%20and%20Revision%20Aids/past%20papers/Unit%205%20June%202007.pdf
Original post by starfish232
Could someone please answer a few questions I have about the specimen paper:
1. 2c(ii) says that 'Four moles gaseous reactant forming' but isn't it three?
2. 3b(i) - I don't understand how this question has been done
3. 3b9ii0 - Cell e.m.f is 0.06 V but I got 0.60V (0.77-0.17) - I don't understand how it's 0.06V

http://filestore.aqa.org.uk/subjects/AQA-CHEM5-W-SQP-07.PDF
http://filestore.aqa.org.uk/subjects/AQA-CHEM5-W-SMS-07.PDF


my guess is specimen papers are usually ridiculed with errors

Original post by starfish232


Think of it as an equation, to normally find enthalpy formation its equal to everything else added together.

-642=150+242+736+x-728-2493 (x is the unkown)
just rearrange
-x=150+242+736+642-728-2493
-x=-1451
x=1451
Reply 1045
Avatar for samfreak
samfreak
if the surface area of the positive electrode increased what would be the effect on the emf?

Posted from TSR Mobile
Reply 1046
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samfreak
in the january 2010 paper question 8a to do with electronegativity, in the mark scheme it states that the attraction of bond pair to nucleus increases? what bond pair is it on about?

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Leaving past papers till last few days lol

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Original post by samfreak
if the surface area of the positive electrode increased what would be the effect on the emf?

Posted from TSR Mobile


Would there be no effect ... it's an equilibrium reaction, and increasing the surface area of a catalyst would have no effect on the emf, it would just mean that the reaction would reach equilibrium quicker...

That's my opinion anyway, and my chemistry teacher said pretty much the same thing. :smile:
Original post by idunnotbh
hey guys random question here but can anyone confirm this for me please...

we do NOT have to learn the half equations and overall equations of re chargeable batteries and non re chargeable batteries, for example for lead acid batteries or zinc/carbon like in the text book?

thank you


i don't think so. I am just in case, but just need to be able to know how to derive them. I think...
Reply 1050
Avatar for samfreak
samfreak
Original post by igobyursula
Would there be no effect ... it's an equilibrium reaction, and increasing the surface area of a catalyst would have no effect on the emf, it would just mean that the reaction would reach equilibrium quicker...

That's my opinion anyway, and my chemistry teacher said pretty much the same thing. :smile:


thanks :-)

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In the book the spectrometry method is changing the vol of the ions, but everywhere else spectrometry is changing the frequency of visible light through a sample of a coloured complex (to see absorption). Is there a right one/preferred answer?
Reply 1052
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crc290
14
Original post by samfreak
in the january 2010 paper question 8a to do with electronegativity, in the mark scheme it states that the attraction of bond pair to nucleus increases? what bond pair is it on about?

Posted from TSR Mobile


The pair of electrons shared in the bond between an atom of a period 3 element and any random atom. There isn't a specific bond in the question because you're supposed to realise that electronegativity only applies to bonds (at least at A-level it does)
Reply 1053
Avatar for charch95
charch95
Original post by Crazy Crouton
Has anyone done the exam style paper in the back of the nelson thrones textbook? It seems quite weird and synoptic...


Yeah, my teacher says the questions in the Nelson Thornes book aren't that great as some are taken from the old syllabus apparently.
Original post by charch95
Yeah, my teacher says the questions in the Nelson Thornes book aren't that great as some are taken from the old syllabus apparently.


The style of the old syllabus questions are a bit different I think. I'm doing them anyway just in case AQA decide to be a bit experimental this year. I suppose they are helpful in solidfying certain concepts...

Though in some of the Unit 5 questions, there are some Unit 4 stuff,which I am ignoring:smile:
Chem 5 is on the day of my birthday, so I hope it won't be too bad.... :smile:
Slightly panciking with the calcs on moles in this unit..... For the jan 2010 paper question 8c... how do we know it forms that??? and how do we know the equation???

IT would be very helpful if someone can tell me a step by step method of approaching these calcs questions
Original post by lifeisgood2012
Slightly panciking with the calcs on moles in this unit..... For the jan 2010 paper question 8c... how do we know it forms that??? and how do we know the equation???

IT would be very helpful if someone can tell me a step by step method of approaching these calcs questions


The issue with the calculations on Unit 5 is that there are different types of calculations that they may ask you. For example, they could ask you about redox titrations, or a back titration.

In this example, and I have it in front of me now, there are two main equations.

i) a periodicity equation. The reaction between P4O10 and 6H20 to form 4H3PO4

ii)acid-base neutralisation between NaOH and Phosphoric Acid.

You work out the moles of Sodium Hydroxide using the conc. and the volume given. You use the ratios in your Acid-base neutralisation equation between the sodium hydroxide and the phosphoric acid to work out the moles of phosphoric acid. From that you can work out the initial amount of P4O10 using the equation between P4O10 and 6H20.

There isn't really any universal step by step method on these kind of questions as they may be asking for different things. I just keep practising them.
(edited 10 years ago)
Original post by JSN
+ can some explain why the reactions with en will be different for 8ei and ii

http://filestore.aqa.org.uk/subjects/AQA-CHEM5-QP-JAN12.PDF


Hiya...

Sorry if someone else has already answered this question for you.

With 2+ hexa-aqua ions, basically (well my chemistry teacher told me because there is no distinction in the book(s))

Its 3en which forms [M(en)3]2+ + 6H2O

With 3+ hexa aqua ions it does something different.

en is H2NCH2CH2NH2

This is the following equation

2[M(H2O)6 ]3+ + 3H2NCH2CH2NH2 ----> 2[M(H2O)3(OH)3] + 3H3NCH2CH2NH3

This is because 3+ ions are slightly more acidic and can donate H+ more easily. Think of the reactions between the hexa aqua ions and carbonate ions.

Hope this helps. I was completely muddled by it all initially. There is not actually any distinction in the book (I use Nelson Thornes) at all, but I think you are supposed to apply knowledge of the differences between the reactions betweeen carbonate with 2+ hexa aqua ions and 3+ hexa aqua ions. en is a bidentate ligand, as is the carbonate ion.
(edited 10 years ago)
Original post by idunnotbh
thank you! what kind of understanding? lol like basically do you we just need to know that when they're being re charged the equations go the other way?

and to answer your question above, yeah sadly it is :frown:


Yeah exactly! just the definitions of primary and secondary cells, what happens when discharging and recharging etc.... :frown: This is the first time i'm hearing it's synoptic... i know biology is synoptic but chemistry....ah mannnnnnn!!

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