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Help please! Oxidation/Reduction question on iron sulfate :( watch

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    (c) Aqueous iron(II) sulfate takes part in redox reactions.
    Using oxidation numbers, show that both reduction and oxidation have taken place in the
    redox reaction of aqueous iron(II) sulfate shown below.
    6FeSO4 + 7H2SO4 + Na2Cr2O7----> 3Fe2(SO4)3 + Cr2(SO4)3 + Na2SO4 + 7H2O
    ................................ ................................ ................................ ................................ ................................ ................................ ................................ ................................ ............. [2]

    I can do simple redox questions most of the time, but with this i get a little confused.
    Could someone help me with how i would do it?
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    (Original post by ab12345)
    (c) Aqueous iron(II) sulfate takes part in redox reactions.
    Using oxidation numbers, show that both reduction and oxidation have taken place in the
    redox reaction of aqueous iron(II) sulfate shown below.
    6FeSO4 + 7H2SO4 + Na2Cr2O7 3Fe2(SO4)3 + Cr2(SO4)3 + Na2SO4 + 7H2O
    ................................ ................................ ................................ ................................ ................................ ................................ ................................ ................................ ............. [2]

    I can do simple redox questions most of this time, but with this i get a little confused.
    Could someone tell me how i would do it?
    Work out the oxidation state for iron on the left and on the right.

    It has changed by either adding or losing electrons. You have to decide which.

    Then do the same for chromium.
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    (Original post by charco)
    Work out the oxidation state for iron on the left and on the right.

    It has changed by either adding or losing electrons. You have to decide which.

    Then do the same for chromium.

    I understand that at the start Fe = +2 and Cr = +6
    but then..
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    (Original post by ab12345)
    I understand that at the start Fe = +2 and Cr = +6
    but then..
    So what is the oxidation state of iron in Fe2(SO4)3 ?

    and chromium in Cr2(SO4)3 ?
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    (Original post by charco)
    So what is the oxidation state of iron in Fe2(SO4)3 ?

    and chromium in Cr2(SO4)3 ?
    :confused:
    Could you explain how i would do that please?
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    (Original post by ab12345)
    :confused:
    Could you explain how i would do that please?
    Well you know that the SO4 ion has a 2- charge. So if there are 3 sulphate ions there is an overall negative charge of 6. There are also 2 iron ions in that compound. The charge of the 2 ions must add up to +6 to balance out the -6. That means the charge of each Fe ion is +3. So their oxidation state is +3. Which is an increase from +2, so they have been oxidised.

    Now do the same with Chromium, you should find that the oxidation state has decreased which means they have been reduced.
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    (Original post by fudgesundae)
    Well you know that the SO4 ion has a 2- charge. So if there are 3 sulphate ions there is an overall negative charge of 6. There are also 2 iron ions in that compound. The charge of the 2 ions must add up to +6 to balance out the -6. That means the charge of each Fe ion is +3. So their oxidation state is +3. Which is an increase from +2, so they have been oxidised.

    Now do the same with Chromium, you should find that the oxidation state has decreased which means they have been reduced.
    Thank you soooo much!
    I had one of those moments when i kept thinking SO4 was -1
    No wonder i kept getting it wrong haha

    Thanks again
 
 
 
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