Join TSR now and get all your revision questions answeredSign up now
    Offline

    12
    ReputationRep:
    (Original post by Lucy-1995)
    This may sound stupid, but whats valence??
    valence is typically, the number of electrons needed to fill the outermost shell of an atom.
    so carbon has a valence of 4 because it needs 4 electrons to fill its outer shell which is why it forms 4 bonds with other elements.
    Offline

    0
    ReputationRep:
    I came across these questions in the Jan 12 paper, and I got really confused..

    8e) Diaminoethane (H2NCH2CH2NH2), like ammonia, can react as a base and as a ligand.

    8ei) Write an equation for the reaction that occurs between an aqueous solution of aluminium chloride and an excess of aqueous diaminoethane.

    8eii) Write an equation for the reaction that occurs between an aqueous solution of cobalt (II) sulphate and an excess of aqueous diaminoethane.

    Ok so in the first question, the answer was 2[Al(H2O)6]3+ + 3H2NCH2CH2NH2 --> 2[Al(H2O)3(OH)3] + 3[H3NCH2CH2NH3]2+ ... so the diaminoethane is acting as a BRONSTED LOWRY BASE (proton acceptor).

    In the second question, the answer was [Co(H2O)6]2+ + H2NCH2CH2NH2 --> [Co(H2NCH2CH2NH2)3]2+ + 6H2O .... so acting as a LEWIS BASE or a LIGAND (lone pair donor).

    I understand how both these reactions work, but what I don't understand is how do I know which reaction to write for each question? Because they are both worded exactly the same! Or am I being completely stupid (which is actually rather likely)

    X
    Offline

    0
    ReputationRep:
    All we need to know about DeltaE = hv is what it stands for dont we?
    Offline

    12
    ReputationRep:
    (Original post by gooner1886)
    All we need to know about DeltaE = hv is what it stands for dont we?
    Yes, no calculations
    Offline

    0
    ReputationRep:
    (Original post by cuckoo99)
    valence is typically, the number of electrons needed to fill the outermost shell of an atom.
    so carbon has a valence of 4 because it needs 4 electrons to fill its outer shell which is why it forms 4 bonds with other elements.
    Oh okay thanks
    Offline

    3
    ReputationRep:
    (Original post by RoaringLion)
    What synoptic stuff do we need to know?


    Posted from TSR Mobile
    Unit 5 is not synoptic unlike AQA biology.
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by frogs r everywhere)
    Unit 5 is not synoptic unlike AQA biology.
    It is synoptic to Units 1 and 2, mostly Unit 1
    Offline

    2
    ReputationRep:
    Can someone explain to me why on the Jan12 paper, Q4(e)(i) the equation is 2Fe3+ + H2 --> 2Fe2+ + 2H+ instead of 2Fe2+ + 2H+ --> 2Fe3+ + H2 ????
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by tr12)
    Can someone explain to me why on the Jan12 paper, Q4(e)(i) the equation is 2Fe3+ + H2 --> 2Fe2+ + 2H+ instead of 2Fe2+ + 2H+ --> 2Fe3+ + H2 ????
    You have to look at which is being oxidised and reduced in order to make the overall equation for the cell. In this instance, the Fe3+ electrode has a higher pd and is therefore being oxidised and so stays the way it is, whereas the H+ electrode is being reduced, so you have to flip the sign over before combining the two equations

    I realise that sounds a little disjointed, ask for further clarification if needed
    Offline

    0
    ReputationRep:
    (Original post by cuckoo99)
    Yes, no calculations

    Delte E = energy gained by electrons
    H = plancks constant
    v = frequency of light absorbed

    And thats it right?
    Offline

    5
    ReputationRep:
    (Original post by gooner1886)
    Delte E = energy gained by electrons
    H = plancks constant
    v = frequency of light absorbed

    And thats it right?
    That is correct, thank God I do physics, didn't have to learn much new stuff for that part
    Offline

    0
    ReputationRep:
    I came across these questions in the Jan 12 paper, and I got really confused..

    8e) Diaminoethane (H2NCH2CH2NH2), like ammonia, can react as a base and as a ligand.

    8ei) Write an equation for the reaction that occurs between an aqueous solution of aluminium chloride and an excess of aqueous diaminoethane.

    8eii) Write an equation for the reaction that occurs between an aqueous solution of cobalt (II) sulphate and an excess of aqueous diaminoethane.

    Ok so in the first question, the answer was 2[Al(H2O)6]3+ + 3H2NCH2CH2NH2 --> 2[Al(H2O)3(OH)3] + 3[H3NCH2CH2NH3]2+ ... so the diaminoethane is acting as a BRONSTED LOWRY BASE (proton acceptor).

    In the second question, the answer was [Co(H2O)6]2+ + H2NCH2CH2NH2 --> [Co(H2NCH2CH2NH2)3]2+ + 6H2O .... so acting as a LEWIS BASE or a LIGAND (lone pair donor).

    I understand how both these reactions work, but what I don't understand is how do I know which reaction to write for each question? Because they are both worded exactly the same! Or am I being completely stupid (which is actually rather likely)

    X
    Offline

    2
    ReputationRep:
    (Original post by Sherlockedd)
    You have to look at which is being oxidised and reduced in order to make the overall equation for the cell. In this instance, the Fe3+ electrode has a higher pd and is therefore being oxidised and so stays the way it is, whereas the H+ electrode is being reduced, so you have to flip the sign over before combining the two equations

    I realise that sounds a little disjointed, ask for further clarification if needed
    How did you know Fe3+ had a higher pd?
    Offline

    0
    ReputationRep:
    What effect does the concentration of reactants have in electrochemical cells.
    Example: In a zinc and Iron cell, what effect does changing concentrations of zinc or iron have on emf?
    Offline

    2
    Can anyone tell me how you would write an equilibirum expression for this?
    Offline

    3
    ReputationRep:
    (Original post by Sherlockedd)
    It is synoptic to Units 1 and 2, mostly Unit 1
    Compared to biology, not really.
    Well, A2 candidates are expected to know how to do simple molar calculations etc.
    I did Chem5 in January with no knowledge of Chem4.
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by tr12)
    How did you know Fe3+ had a higher pd?
    Well the SHE has a pd of 0 by definition and it shows on the table they give you in the paper that Fe3+ has a positive pd
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by frogs r everywhere)
    Compared to biology, not really.
    Well, A2 candidates are expected to know how to do simple molar calculations etc.
    I did Chem5 in January with no knowledge of Chem4.
    Yeah, but chem 5 is not synoptic to chem 4, only to chem 1 and 2 :L
    Offline

    1
    ReputationRep:
    like in unit 2, do you get full marks just for the right answer in calculations or it is step by step marking? lol poor chemistry, been neglected by me over the weekend till bio5 has been castrated.
    Offline

    12
    ReputationRep:
    (Original post by frogs r everywhere)
    Compared to biology, not really.
    Well, A2 candidates are expected to know how to do simple molar calculations etc.
    I did Chem5 in January with no knowledge of Chem4.
    its sinoptic for AS topics. lots of stuff from unit 1 chemistry comes up in unit 5, like electronegativity and intermolecular forces. also stuff from unit 2 like enthalpy of formation and bond enthalpys.
 
 
 
Poll
If you won £30,000, which of these would you spend it on?

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

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