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Homework Help: Complete equation, then balance

  1. Nov 26, 2011 #1


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    1. The problem statement, all variables and given/known data
    This is a single displacement reaction
    aluminum + hydrochloric acid -->

    2. Relevant equations

    3. The attempt at a solution
    Since I know its single displacement, and I know that aluminum can't trade places with chlorine because one is a metal and one is a non-metal, aluminum must trade places with hydrogen, which I know can trade places with a metal.

    Al + HCl --> H + AlCl

    Since I know that hydrogen is a diatomic element, I must change it to H2

    Al + HCl --> H2 + AlCl

    Now it's out of balance because there are 2 hydrogens on the right. So I balance it by multiplying the left HCl by 2.

    Al + 2HCl --> H2 + AlCl

    This leaves Cl out of balance, so I multiply the right one by 2.

    Al + 2HCl --> H2 + 2AlCl

    This leaves Al out of balance, so I multiply the left one by 2.

    2Al + 2HCl --> H2 + 2AlCl

    Seems to be balanced now. But when I look up the answer by Googling, I find that I should have ended up with
    2Al + 6HCl --> 2AlCl3 + 3H2

    Where did I go wrong? Thanks!
  2. jcsd
  3. Nov 26, 2011 #2


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    Staff: Mentor

    Balancing was correct, but as you assumed wrong formula for aluminum chloride, effort was wasted.
  4. Nov 26, 2011 #3


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    thanks Borek. I knew it was something simple I was missing!
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