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    (Original post by volvicstar)
    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!
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    (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?
    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)
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    (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
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    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?
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    Can anyone explain to me Q6b(ii) and Q4b(ii) Jan 2011 paper?

    have no idea what to do!

    Thanks
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    Does anyone have a list of all the colours of compounds/transition metals we need to know!!!
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    (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
    • Thread Starter
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    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
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    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?
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    Guys any methods to remember the colour of transiton metals at different oxidation states apart from writing it on the back of your calculator?
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    (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
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    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
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    (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. Know the common colours for precipitation reactions and ligand substitutions well anyway because they are the most common questions.


    (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.
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    (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.
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    why is kw = [H+] squared

    when finding pH of pure water in jan 2011 paper

    am completely confused lol
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    (Original post by Pandit Bandit)
    why is kw = [H+] squared

    when finding pH of pure water in jan 2011 paper

    am completely confused lol
    Because Water is a weak acid, so Kw is basically Ka in that sense as Kw= [H+][OH-] and because H2O dissociates like this [H+][OH-] = [H+]2 (Kw)
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    ahh kk thanks!
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    too lazy to do the 40 long t metal questions.
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    Anyone know if we're meant to remember the names/pH ranges of indicators? Can't find a spec' sheet anywhere to find out.

    Cheers
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    just had the ocr biology F215 exam and it went really bad
    cant motivate myself to even try and revise for chemistry
 
 
 
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