Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Complete equation, then balance

  1. Nov 26, 2011 #1


    User Avatar
    Science Advisor
    Gold Member

    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


    User Avatar

    Staff: Mentor

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


    User Avatar
    Science Advisor
    Gold Member

    thanks Borek. I knew it was something simple I was missing!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook