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

how do you get to the revision questions?

hey

if you go back to my original quote to say thanks and click on the link, it will take you into a new window with the attached files. Just click on them and they should open!

Reply 821

Jtking3000

13

Original post by ChubbyRain

I thought you just needed to know what occurs at the positive and negative electrode in terms of hydrogen and oxygens half equations, as well as pros and cons of fuel cell etc.

Another general question to all, about ionic charge, in the OCR textbook it says that ionic charge ncreases and ion radius decreases on pg 176 if anyone has the same book, why does the ionic radius decrease from Na+ -- Mg2+ --- Al3+, if you look at the periodic table their ionic radius increases? :s-smilie:

As you go across the period each element gets an extra electron and a proton, the electrons are added to the same shell but the increased nuclear charge pulls the electrons in slightly more hence the radius decreases across the period (basically atoms, bonds and groups explanation)

Reply 822

ChubbyRain

Original post by Jtking3000

As you go across the period each element gets an extra electron and a proton, the electrons are added to the same shell but the increased nuclear charge pulls the electrons in slightly more hence the radius decreases across the period (basically atoms, bonds and groups explanation)

Ohhh okay thank you! So basically increased nuclear charge makes everything pulled in and smaller.. wicked :smile:

Reply 823

Vidja

Does anyone know of any websites where you can just test knowledge with questions and quick answers? I'm thinking something along the lines of mathsnet but with chemistry?

Reply 824

Pandit Bandit

Can anyone explain to me Q6b(ii) and Q4b(ii) Jan 2011 paper?

have no idea what to do!

Thanks

Reply 825

SmartFool

Does anyone have a list of all the colours of compounds/transition metals we need to know!!!

Reply 826

haydyb123

9

Original post by SmartFool

Does anyone have a list of all the colours of compounds/transition metals we need to know!!!

There was a list a couple of pages back, I reckon 33-38 if of course you don't mind looking :smile:

Reply 827

Ecstacy.

OP

Hows is everybody spending the last 2 days? Going over notes or past papers?
I prefer going through my notes and writing them out the last 2 days just incase i forget stuff for the exam :smile:

Reply 828

Student21

8

Im going through the past papers now. Can anyone explain to me how to do question 7 on the June 2010 paper. How do i get the empirical formula when there is no mass given. Do i assume a mass and just work with that?

Reply 829

voices1

Guys any methods to remember the colour of transiton metals at different oxidation states apart from writing it on the back of your calculator?

Reply 830

haydyb123

9

Original post by voices1

Guys any methods to remember the colour of transiton metals at different oxidation states apart from writing it on the back of your calculator?

As it tedious as it sounds, write and rewrite, 3-4 times should be enough, and then write out once a night between now and the exam, and you'll find you can recall them quickly. Corresponding colours should be useful to write them with...
Sometimes I'm glad to took Psychology at AS

Reply 831

Azizo

Hey guys, could some one possibly upload the a2 chem exam cafe answers pdf, my CD broke and i could really do with the answers... I can only find AS ones on here.. Thanks :smile:

Reply 832

hiyarearl

4

Original post by voices1

Guys any methods to remember the colour of transiton metals at different oxidation states apart from writing it on the back of your calculator?

Look over the grid in the book just before you go into the exam and then quickly jot down the grid somewhere on the formula sheet or something as soon as you get in (when you are allowed to start the exam). If you can hold the colours in your head for the few minutes between getting into the exam hall and getting the paper to write on then you're fine. :tongue:

Know the common colours for precipitation reactions and ligand substitutions well anyway because they are the most common questions. :smile:

Original post by Student21

Im going through the past papers now. Can anyone explain to me how to do question 7 on the June 2010 paper. How do i get the empirical formula when there is no mass given. Do i assume a mass and just work with that?

I'll explain how I just did this and maybe you may find my method clearer:

June 2010 Question 7:

A) 5H2O2 ---> 10e- + 5O2 + 10H+

H2O2 ---> 2e- + O2 + 2H+

The reason for this because you can see by comaping the overall equation and the half equation you are given that O2 is in the half equation and not the overall equation so it must be a product of the H2O2 half equation. As for the electrons you can see all the balancing numbers have been multiplied by 2 in the overall equation and H2O2 has the balancing number 5. This must have been done to make the electron balancing numbers equal so we can deduce the electron balancing number in our half equation is 10 and then by looking at the difference in the H+ balancing numbers we can see that our balancing number must be (8x2 = 16), 16- x = 6. Therefore x, our balancing number must be 10.

B) 25 cm3 solution of H2O2 --- > diluted up to 250cm3 ---> 25cm3 titration

23.45 x 0.02 / 1000 = mols of MnO4-

(mols of MnO4- / 2 ) x 5 = mols of H2O2 in 25cm3 titration

mols of H2O2 x 10 = mols of H2O2 in 250 cm3 diluted solution

Apply n = cv/1000

(mols of H2O2 in 250cm3 diluted solution x 1000) / 25 = 0.469 mol dm3

To convert to g dm3 multiple by the relative atomic mass as mol x relative atomic mass = g

= 15.946 g dm3

Hope that helps. :smile:

Reply 833

voices1

Original post by haydyb123

As it tedious as it sounds, write and rewrite, 3-4 times should be enough, and then write out once a night between now and the exam, and you'll find you can recall them quickly. Corresponding colours should be useful to write them with...
Sometimes I'm glad to took Psychology at AS

thanks.

Reply 834

Pandit Bandit