Hey there! Sign in to join this conversationNew here? Join for free
x Turn on thread page Beta
    Offline

    0
    ReputationRep:
    (Original post by Sparkly-Star)
    So Pt is used in conventional cell diagrams if there is no solid? Someone said this yesterday. :p: Just wanna confirm. Thanks.
    Yep, used as the electrode
    Offline

    0
    ReputationRep:
    7f) and 9c ii) on january 20100 any ideas??? any help would be appreciated
    Offline

    5
    ReputationRep:
    Im sorry if this question has already been asked....but why is first electron affinity exothermic and second electron affinity endothermic??? Thanks
    Offline

    0
    ReputationRep:
    (Original post by Sparkly-Star)
    So Pt is used in conventional cell diagrams if there is no solid? Someone said this yesterday. :p: Just wanna confirm. Thanks.
    Yes because it isn't possible to get a non-solid electrode
    Offline

    0
    ReputationRep:
    When drawing the structures for complexes like in Jan 2011 question 4, do you need to show co-ordinate bonds, or are you just ok with a normal dash?
    Offline

    2
    ReputationRep:
    Good luck everyone ! My last exam, only need a C in this one and feeling confident so no more revision for me
    Offline

    1
    ReputationRep:
    (Original post by mkb230)
    Good luck everyone ! My last exam, only need a C in this one and feeling confident so no more revision for me
    I only need a C too but I can't possibly go in without knowing absolutely everything which is daft but hey
    Offline

    0
    ReputationRep:
    Hey, Im looking at Jan 2010 q3b - and I dont understand why they've used that particular O2 half equation?

    Will rep
    Offline

    0
    ReputationRep:
    (Original post by lemontang1)
    Im sorry if this question has already been asked....but why is first electron affinity exothermic and second electron affinity endothermic??? Thanks
    Negative ion after the first E.A. therefore they repel - something like this anyway (for endothermic). For exothermic (first E.A.) its because adding the electron makes it more stable
    Offline

    0
    ReputationRep:
    (Original post by fivepoundoff)
    When drawing the structures for complexes like in Jan 2011 question 4, do you need to show co-ordinate bonds, or are you just ok with a normal dash?
    You have to draw an arrowed bond with the arrow pointing from the atom donating the lone pair to the atom accepting
    Hope this helps, and good luck!
    Offline

    0
    ReputationRep:
    (Original post by jwest)
    7f) and 9c ii) on january 20100 any ideas??? any help would be appreciated
    7 f) [Co(Cl4)]2-

    This is because Cl- are bigger than H20 molecules so you can only fit 4 around



    9 c) It would start off slow because both the ions repel each other. As some Mn2+ is produced the reaction gets faster because this catalyses the reaction which produces more Mn2+ and further speeds up the reaction (may want to check this )
    Offline

    1
    ReputationRep:
    (Original post by king101)
    Can you please explain this dissociation/Enthalpy of... I hate it :P Only part im a little confused on
    Ok, it'll be better if we use chlorine as an example:
    The enthalpy of atomisation of chlorine results in 1 mole of Cl. So if you have NaCl, you keep this value the same. If you have MgCl2 on the other hand, you double it.

    The enthalpy of dissociation, as well as the mean bond enthalpy, of chlorine results in 2Cl since you're breaking one mole of Cl-Cl bonds. If you have NaCl, you halve this figure, if you have MgCl2, you keep it the same.


    (Original post by strawberry_cake)
    I meant for the jan ones
    Don't think there are any Jan ones for those years
    Offline

    0
    ReputationRep:
    (Original post by lemontang1)
    Im sorry if this question has already been asked....but why is first electron affinity exothermic and second electron affinity endothermic??? Thanks
    1st is exo because you're adding 1 electron to a gaseous atom, and the electron is attracted to the positive nucleus, so energy is released.
    2nd is endo because you're adding 1 electron to a negative ion. Both are negatively charged; like charges repel, so you've got to put energy in to make the negative ion accept the electron.

    Why does Chapter 15 have to have so many equations.. theres too many!
    Offline

    2
    ReputationRep:
    (Original post by jwest)
    7f) and 9c ii) on january 20100 any ideas??? any help would be appreciated
    7f) It's [CoCl4]^2-

    Because [Co(H2O)6]^2+ + 4Cl- --> [CoCl4]^2- + 6H2O

    And the explanation for the co-ordination number: Cl- is too large of an ion to fit 6 around the transition metal. The repulsive forces make it impossible.

    9c ii) You'd draw the curve starting slowly because the ions repel each other. Then rapidly decreasing because Mn2+ ions autocatalize the reaction. The more Mn2+ are formed they catalyse their own production. It would level out at the end because all of the MnO4- would be used up as it goes to completion.

    Edit: Too slow lol
    Offline

    0
    ReputationRep:
    (Original post by lemontang1)
    Im sorry if this question has already been asked....but why is first electron affinity exothermic and second electron affinity endothermic??? Thanks
    first electron affinity is exothermic because there is no repulsion in this reaction and so the say its a cl atom it can more easily gain an electron without any problem, while say cl- adding an electron to this is second elctrona ffinity and has a nagative charge so there is repulsion which means that it is endothermic as energy has to be put in to keep this electron and negatively charged ion together
    Offline

    0
    ReputationRep:
    (Original post by Anon1993)
    Hey, Im looking at Jan 2010 q3b - and I dont understand why they've used that particular O2 half equation?

    Will rep
    If they used the first O2 equation then the 4H+ would react with the 4OH- on the bottom equation, therefore it wouldn't be in alkaline conditions (I think). But using the second one you'll end up with 4OH- cancelling but its still in alkaline conditions.

    ...thats my guess
    Offline

    0
    ReputationRep:
    I only need a D to get my predicted grade overall yet I'm still bricking it.
    Offline

    0
    ReputationRep:
    (Original post by IFondledAGibbon)
    7f) It's [CoCl4]^2-

    Because [Co(H2O)6]^2+ + 4Cl- --> [CoCl4]^2- + 6H2O

    And the explanation for the co-ordination number: Cl- is too large of an ion to fit 6 around the transition metal. The repulsive forces make it impossible.

    9c ii) You'd draw the curve starting slowly because the ions repel each other. Then rapidly decreasing because Mn2+ ions autocatalize the reaction. The more Mn2+ are formed they catalyse their own production. It would level out at the end because all of the MnO4- would be used up as it goes to completion.

    Edit: Too slow lol
    ok, thanks for the help
    Offline

    0
    ReputationRep:
    (Original post by WJD)
    I only need a D to get my predicted grade overall yet I'm still bricking it.
    how do you know this, did you do chem4 in jan and you got youe prac mark?

    i sat chem 4 a week ago, and did the chem empa so jus gonna get as high as i can. got a fairly decent as grade so hoping for an a overall
    Offline

    0
    ReputationRep:
    (Original post by fivepoundoff)
    If they used the first O2 equationn then the 4H+ would react with the 4OH- on the bottom equation, therefore it wouldn't be in alkaline conditions (I think). But using the second one you'll end up with 4OH- cancelling but its still in alkaline conditions.

    ...thats my guess
    Thanks. . i kind of get it, but in the next part, 3c, i dont understand why they have an OH- in the hydrogen half cell bit?
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: August 20, 2011
Poll
Do you agree with the proposed ban on plastic straws and cotton buds?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.