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Homework Help: Balancin an equation

  1. Nov 28, 2005 #1
    balancin an equation!!!

    hello everybody,
    i just got back from my chemistry class, with some homework...
    it s about balancin equations (hard ones) and they are relating to the lesson of oxidation-reduction...
    here is one of them that i have to balance--
    if someone can show me the steps to take, that would be awesome :) because i have like 5 more to do...

    Al + H2SO4 --> Al 3+ + SO4 2- + SO2 + H2O

    thank you :)

    oh yeah, the problem in this equation is that i have SO4 2- and SO2
    so to determine the number of oxydation for S
    should it be -8 or -4 ==> should i use SO4 -2 or SO2

    when i know what to use, i ll see the change of this number, then what ?
     
    Last edited: Nov 28, 2005
  2. jcsd
  3. Nov 28, 2005 #2
    use both [itex] {SO}^{-2}_4 [/itex] and [itex] SO_2 [/itex]
    gah sorry i can't get the LaTeX to work ...
     
    Last edited: Nov 28, 2005
  4. Nov 28, 2005 #3
    hmm
    so would i use the oxydation number of -8 or -4
     
  5. Nov 28, 2005 #4
    for [itex] {SO}^{-2}_4 [/itex] the oxidation number of sulfur is +6 (O is -2, the total charge is -2, so [itex] -2 \times 4 + S = -2 [/itex] and [itex] S = +6 [/itex]

    the oxidation number of S in [itex] SO_2 [/itex] is +4
     
  6. Nov 28, 2005 #5
    okay, so when i want to see the change of the number of oxidation S, to find the coefficient for balancin the reaction; would i do:
    (+6) - (+6) = 0
    or
    (+4) - (+6) = -2

    ??
    thanks
     
  7. Nov 28, 2005 #6
    yeah, that's right.
     
  8. Nov 28, 2005 #7
    ummm... i think i asked for WHICH ONE TO USE!
    ...
     
  9. Nov 28, 2005 #8
    oh haha sorry. you need to use both of them

    so write a redox half reaction for both

    dont forget the Al
     
  10. Nov 29, 2005 #9
    still dont get how to really do it... if anyone can give me some steps for this one!
    thanks
     
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