1. Because the reaction is: HC2H3O2(aq) H+1(aq) + C2H3O2-1(aq)
    we know that for every acetic acid molecule that dissociates we will get one hydrogen ion and one acetate ion. This can be represented algebraicly in the following manner:
    Initial Concentrations
    Equilibrium Concentrations
    [HC2H3O2] = 3.0 M
    [H+1] = 0.50 M
    [C2H3O2-1] = 0.50 M
    [HC2H3O2] = 3.0 - x
    [H+1] = 0.50 + x
    [C2H3O2-1] = 0.50 +x
  2. At equilibrium we know that = 1.8x10-5
  3. Substituting the equilibrium concentrations above we get:
  4. Next set up a quadratic equation:
  5. Find possible solutions for x:
  6. Notice that only one solution for x makes physical sense: -0.49
  7. If we use -0.51 for x then we would end up with negative equilibrium concentrations, a physcial impossibility.
  8. Solving the equations above gives us equilibrium concentations of:
    [HC2H3O2] = 3.49M
    [H+1] = 0.01M
    [C2H3O2-1] = 0.01M