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AQA - Unit 5 - Energetics, Redox and Inorganic Chemistry

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Original post by Sparkly-Star
It's funny how I've not learnt about the perfect ionic model from my book.


:rofl: me too :biggrin:
anyone done the jan 11 q7c? im stuck
Reply 962
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jwest
yeh im really not keen on the whole perfect ionic model malarchy but it came up in january so shouldn't come up hugely this time round?
Reply 963
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508836
3
I need help on question 1d ii (June 2010) Why is the reaction endothermic? :s-smilie:
If we had those papers first I wouldn't have known, I know which bit it relates to from my book. But I wouldn't have known tbh.
Reply 965
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Y.D
Original post by Sparkly-Star
It's funny how I've not learnt about the perfect ionic model from my book.


Seconded
Reply 966
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Mazii
Original post by T-Toe
I need help on question 1d ii (June 2010) Why is the reaction endothermic? :s-smilie:


It's an exothermic reaction as delta H is negativee
Reply 967
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jwest
when drawing electrochemical cells, do you only use a 'l' if there is a change of state and a ',' if they are in the same state???
Reply 968
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uxa595
21
I'm starting revision now, i think i may fail this one .... 0o
Reply 969
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kingjohno
Original post by jwest
when drawing electrochemical cells, do you only use a 'l' if there is a change of state and a ',' if they are in the same state???


Yes.
Reply 970
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NRican
Original post by jwest
when drawing electrochemical cells, do you only use a 'l' if there is a change of state and a ',' if they are in the same state???


I would like to know this too, change of state as in aq to s or oxidation state?

Also I can;t get my head around colorimetry, can anyone please summarise it for me :s-smilie:

TIA
Original post by jwest
when drawing electrochemical cells, do you only use a 'l' if there is a change of state and a ',' if they are in the same state???


Yeah. A | represents a phase boundary, so different phases need | between them.

But in mark schemes, most allow | instead of ,
But none allow , instead of |

So if in doubt, use | :smile:
Reply 972
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Zabukar
Were can I find the Answers for the Exam questions in the Aqa Chem text book by Nelson thornes ?
Reply 973
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jwest
Original post by xX.Sabeel.Xx
anyone done the jan 11 q7c? im stuck


h2o2 -> o2 + 2H+ + 2e-

Mno4 2- + 8H+ +5e- -> Mn2+ + 4h20

times peroxide by 5 and maganate by 2

gives 5h2o2 + 2mno4 2- + 16H+ ---> 2Mn2+ + 5o2 + 10 H+ +8H2o

cancel 10H+

5h202 + 2Mno4 2- + 6H+ --> 2Mn2+ + 502 + 8h20

react on a 2:5 ratio in mangante = 4.55 x 10^-4 moles of mangate
therefore 1.138 x 10^-3 moles of peroxide in 25cm3

so 1.138 x 10^-2 in 250cm3 of solution which means that many moles in original 5cm3

c=n/v 1.138 x 10^-2 / 5/1000 = 2.276 mol/dm3

hope this follows ok
Reply 974
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m0man
9
I'm confused as to when you use state symbols and when you don't... anyone know the rule?
Reply 975
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jwest
Original post by Luke0011
Yeah. A | represents a phase boundary, so different phases need | between them.

But in mark schemes, most allow | instead of ,
But none allow , instead of |

So if in doubt, use | :smile:


handy and dandy, cheers for that tip, so basically if in doubt use ,
Original post by strawberry_cake
I only started papers today and didnt have enough time to do them so just read through them.. I hope they've settled in :cry2: I think I'm gonna go through the spec now and go through the 'leftovers'. Chem5's boring me :frown: How are you finding the papers? :smile: The old spec were a lot easier then the new ones i think :/


Yeh the reason the new ones are more challenging is because like the titration questions, they make you find percentages of impurites etc...

I had dont lots in school, but I had to leave it since I had exams so I kinda forgot what kinda questions came up, also need to read over the book again because youll always find youve forgotten something,

I would suggest you actually do the jan 11 paper if you havent already jus so you get a feel of the real thing they tend to be very similar, and as for content, the worst parts are the amount of equations that you have to store in youre memory,

Oh and i also got 'leftovers' lol, dont we all :tongue:
Reply 977
Avatar for JJ 91
JJ 91
hi can someone please help me with question 3e on the jan 2011 paper
Original post by jwest
handy and dandy, cheers for that tip, so basically if in doubt use ,


Nooo, if in doubt use phase boundary: |
haha :smile:
Original post by m0man
I'm confused as to when you use state symbols and when you don't... anyone know the rule?


Only use it if they ask, but you should use it in conventional cell diagrams.

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