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# AQA - Unit 5 - Energetics, Redox and Inorganic Chemistry watch

1. hey could anyone help me with redox equations im just not sure when you include only one reagent and product for example in the specimen paper,

3 (a)An aqueous solution of sulfur dioxide was reacted in separate experiments as follows.

Reaction 1 with HgO
H2O + SO2 + HgO ? H2SO4 + Hg

Reaction 2 with chlorine
2H2O + SO2 + Cl2 ? H2SO4 + 2HCl

(ii) Show, by writing a half-equation, that this oxidising agent in reaction 1 is an
electron acceptor.
................................ ................................ ................................ ................................ ..
(iii) Write a half-equation for the oxidation process occurring in reaction 2.
................................ ................................ ................................ ................................ ..
(iv) Write a half-equation for the reduction process occurring in reaction 2.
................................ ................................ ................................ ................................ ..

the answer for ii is Hg 2+ + 2e- -------> Hg

the answer for iii is 2H2O + SO2 ? H2SO4 + 2e-

why dosnt the oxygen on the Hg come into the half equation?

Thanks
2. (Original post by jamest92)
Write an equation for NaOH and H3PO4
3NaOH + H3PO4 ---&gt; Na3PO4 + H320

Calculate the number of moles of NaOH and therefore moles of H3PO4
21.2 x 0.5 / 1000 = 0.0106 moles of NaOH
It reacts 3 : 1 so divide by 3
3.53 x10^-3 moles of H3PO4 in 25 cm^3

Work out the number of moles in 25 dm^3
3.53 x10^-3 x 25000000 = 3533.3 moles of h3PO4

Work out the number of moles of P4010
P4010 + 6H20 ---&gt; 4H3PO4
Reacts 1 : 4 so divide by 4
Therefore 883.3 moles of P4O10

m = n x Mr
m = 883.3 x 284
m = 2508572 g

m = 250.9 kg
thank you so much!
3. cheers, for the help Willyg11 and OsmosisJones
4. (Original post by AminaJB)
thank you so much!
anytime
5. the jan 2011 paper was quite easy.. hope its the same for this one
6. (Original post by Thisisj)
do you like it??
Ive just been looking at a few pages on the cgp website and its soo clear and concise
I want it but the exam is tomorrow
Shame you didnt get it earlier! ive had it for As and A2 and ive always used to for my revision cuz its much less complicated than the text book and really good at breaking things down
7. hey could anyone help me with redox equations im just not sure when you include only one reagent and product for example in the specimen paper,

3 (a)An aqueous solution of sulfur dioxide was reacted in separate experiments as follows.

Reaction 1 with HgO
H2O + SO2 + HgO ? H2SO4 + Hg

Reaction 2 with chlorine
2H2O + SO2 + Cl2 ? H2SO4 + 2HCl

(ii) Show, by writing a half-equation, that this oxidising agent in reaction 1 is an
electron acceptor.
................................ ................................ ................................ ................................ ..
(iii) Write a half-equation for the oxidation process occurring in reaction 2.
................................ ................................ ................................ ................................ ..
(iv) Write a half-equation for the reduction process occurring in reaction 2.
................................ ................................ ................................ ................................ ..

the answer for ii is Hg 2+ + 2e- -------> Hg

the answer for iii is 2H2O + SO2 ? H2SO4 + 2e-

why dosnt the oxygen on the Hg come into the half equation?

Thanks
8. (Original post by aurelia_koll)
the jan 2011 paper was quite easy.. hope its the same for this one
Section B was good I hope theres lots of repeated questions in this paper
9. this is just a last minute question...i was wondering whether we would get any synoptic questions...because there seems to be lots of synoptic question in unit 5 past papers (specifically june 2009) ?
10. After reading some of the posts I feel like everyone is miles ahead of me in terms of revision ahh GOD!
11. hey does anyone know what the equation is for fe(h2o)4(oh)2 when it oxidises in air, i know the product is fe(h20)3(oh)3
12. can someone also explain why the melting point of aluminium oxide is lower than magnesium oxide, this seems strange, in the book it says that it has cov bonding and ionic bonding but doesnt the extra cov bonding make it stronger?
13. (Original post by antony172)
this is just a last minute question...i was wondering whether we would get any synoptic questions...because there seems to be lots of synoptic question in unit 5 past papers (specifically june 2009) ?
Is the past paper you are doing CHM5 or CHEM5 ?
If its CHM5 don't worry, thats an old spec paper when unit 4 and unit 5 were mixed together, you wont get asked questions like working out pH and stuff tomorrow
14. Why is Chapter 15 so long!!!!
15. How do you know when to double the enthalpy of atomisation? And how do you know if it's giving you the enthalpy of bond dissociation? What's the difference?

16. Again, do we need to know the redox titration equations? I've learnt all of the other reactions in the book apart from these ones because there's half equations to learn as well which take forever.
17. can anyone explain this to me
why larger ligands result in smaller co-ordination numbers?
18. hey could anyone help me with redox equations im just not sure when you include only one reagent and product for example in the specimen paper,

3 (a)An aqueous solution of sulfur dioxide was reacted in separate experiments as follows.

Reaction 1 with HgO
H2O + SO2 + HgO ? H2SO4 + Hg

Reaction 2 with chlorine
2H2O + SO2 + Cl2 ? H2SO4 + 2HCl

(ii) Show, by writing a half-equation, that this oxidising agent in reaction 1 is an
electron acceptor.
................................ ................................ ................................ ................................ ..
(iii) Write a half-equation for the oxidation process occurring in reaction 2.
................................ ................................ ................................ ................................ ..
(iv) Write a half-equation for the reduction process occurring in reaction 2.
................................ ................................ ................................ ................................ ..

the answer for ii is Hg 2+ + 2e- -------> Hg

the answer for iii is 2H2O + SO2 ? H2SO4 + 2e-

why dosnt the oxygen on the Hg come into the half equation?

Thanks
19. thanks jamest92... yes it was chem 5 june 2009 paper...it was asking to calculate pH and other things things....anyway thats reassuring...the specification doesn't tell anything about so i got a bit worried...=)
20. (Original post by IFondledAGibbon)
How do you know when to double the enthalpy of atomisation? And how do you know if it's giving you the enthalpy of bond dissociation? What's the difference?

Depends on the question and what stats they give you, but when you have something like 1/2Cl2 --> Cl, you need to double it because that's only the atomisation of one mole, and in some haber cycles you need 2 Cl's fully atomised.

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