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Equilibria, Energetics and Elements (F325) - June 2011 Exam.

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Reply 600

student777

Original post by apo1324

Could someone please tell me where 34 has come from in the answer to 7b of the June 2010 paper. :frown:

http://www.ocr.org.uk/download/pp_10_jun/ocr_57551_pp_10_jun_gce_f325.pdf

Thanks.

Isn't that just the Mr of H2O2?

Reply 601

CoventryCity

Original post by apo1324

Could someone please tell me where 34 has come from in the answer to 7b of the June 2010 paper. :frown:

http://www.ocr.org.uk/download/pp_10_jun/ocr_57551_pp_10_jun_gce_f325.pdf

Thanks.

You mean in the mark scheme?

34 is the Molar mass of H202

Reply 602

apo1324

Original post by student777

Isn't that just the Mr of H2O2?

Oh i see, where has 40 come from? :frown:

I can't count. :L The mark scheme multiplies the moles by 40 and 34.

Sorry for the stupid questions.

Reply 603

CoventryCity

Original post by apo1324

Oh i see, where has 40 come from? :frown:

I can't count. :L The mark scheme multiplies the moles by 40 and 34.

Sorry for the stupid questions.

I don't understand where the 40 has come from :confused:

Reply 604

SmartFool

Original post by Jtking3000

http://www.qfpost.com/download.do?get=55fdf8ddc8c4ba8fcf13b8f2f3ff8d26

i've uploaded the examination style question answers if thats what you need :smile:

Thank you sooo much!! :biggrin:

that is exactly what i needed! :biggrin:

Reply 605

Jtking3000

Original post by apo1324

Oh i see, where has 40 come from? :frown:

I can't count. :L The mark scheme multiplies the moles by 40 and 34.

Sorry for the stupid questions.

Original post by CoventryCity

I don't understand where the 40 has come from :confused:

1/0.025, 0.025 being the volume of H2O2

Reply 606

CoventryCity

Original post by Jtking3000

1/0.025, 0.025 being the volume of H2O2

Ahh agreed I forgot you need to divide by volume/1000 :colondollar:

Reply 607

CoventryCity

For the last part of 7b) about the O2 volume how have they done it?

Reply 608

Jtking3000

Original post by CoventryCity

For the last part of 7b) about the O2 volume how have they done it?

for every 2 moles of MnO4- reacting with 5 moles of H2O2 it creates 5 moles of O2 which makes is 1.1725x10^-3 moles in this case since there is 4.69x10^-4 moles of MnO4-

1 mole of O2 occupies 24dm^3 so 1.1725x10^-3 moles of O2 occupies 24x1.1725x10^-3= 0.0281dm^3

basically a recap of atoms bonds and groups.

(edited 12 years ago)

Reply 609

blush.ox

Just redid the jan 2011 and got 80/100 as i thought it would be good practice to do it again :colonhash:

.

First time i did it was in the easter hols when we were yet to finish all the topics and had some thing along the lines of 55/100. There are some questions on here i have absolutely no idea how to answer and staring at the mark sheme until it makes sense isnt helping either :sad:

(edited 12 years ago)

Reply 610

Mie Peson

Could someone please explain to me how to do 6d on jan11 peper. I understand what points we have to mention but I don't understand why the enthalpy change of solution of KF is less negative than of RBF. If K+ ion has a smaller radius, whould it not have more negative enthalpy change of solution as its lattice enthalpy would be more negative...

I would also appreciate some help on the first question of specimen paper on determining rates. This may seem easy and sorry for asking stupid questions.

Thank you

Reply 611

CoventryCity

Original post by Mie Peson

I was confused about this as well but from what I understand it is because a smaller ionic radius will also give a larger exothermic value for the lattice enthalpy. For the enthalpy of solution the lattice has to be broken down so in the Q you have to say the smaller ionic radius has a more significant effect on the lattice enthalpy than the enthalpy of hydration meaning KF will be less exothemic

I'm not sure if I explained that very well or even correctly, we did this Q in lesson today and it was very confusing

Breaking down the lattice is the opposite of lattice enthalpy so is a +ve value with the same magnitude, so the larger the lattice enthalpy means it becomes less exothemic

(edited 12 years ago)

Reply 612

waecskt

I hope theres hairdessing pt II included.

Reply 613

Jtking3000

Original post by waecskt

I hope theres hairdessing pt II included.

My favourite question on Jan 2011 :biggrin:

Reply 614

student777

Original post by waecskt

I hope theres hairdessing pt II included.

This actually made me laugh out loud. Quite an achievement for a chemistry thread :biggrin:

Reply 615

Right Guard 3.D

That was the worst question ever lol nobody I know has got that right.

Probably because I can't perm my hair :frown:

Reply 616

FBPS

Can someone please exaplain to me how you write redox reactions, and half equations?

Reply 617

Mie Peson

Original post by CoventryCity

Yeah that makes sense. I did not think of breaking down of lattice enthalpy being positive. By the way could you please on 2d on specimen paper. I keep on getting 0.013moldm-3 but the answer is 0.13moldm-3.

Thanks again

Reply 618

mauvetard

If you've ever gotten an A in a chemistry module, be it in AS or A2, how did you revise? Did you tackle every past paper in sight? Have extra lessons outside school (tutorials), Read all the way into the night?

Im really curious to know people's revision strategy. I feel the need to change mine... (please quote me when you reply)

Reply 619

student777

Original post by mauvetard

For Atoms, Bonds and Groups, first time round I got a C, retook and got a high A. I basically briefly learnt all the content then did past papers until I literally got sick at the sight of them! You do a few when you start so you know your weak areas. Then go over contennt you keep getting wrong. Then practice exam technique. Practise papers are manna from heaven for me! :P

Though it helped that it was a retake so I already knew most of it, and it's so easy compared to other A2 stuff.

Hope this helps :smile:

Don't ask what i'm doing up at this hour... xD