changing the amount of a substance that participates in an equilibrium

For example: adding Hydrogen ions causes a dislocation of the equilibrium, that will take care that (part of) the extra Hydrogen ions will go away again, by stimulating the forward reaction.
This continues until a new equilibrium is reached.

  1. In the beaker is NH3(aq) (basic environment) with some drops of the indicator methyl red,
    of which the abbreviated formula is: HIn

    Than in the solution the following equilibrium will occur:

        HIn H++ In-
    Red                       Yellow

    The presence of a base (that absorbs H+) means a dislocation of the equilibrium to the right. the yellow color dominates.

  2. Now you add a bit of HCl(aq), the basic environment changes to a less basic or more aced env.

    The acid wil donate H+, so:

    the equilibrium:   HIn H++ In-
                              Red             Yellow

    dislocates to left and the red color will dominate.

  3. Now again we add some base: Nu gaan we weer base toevoegen: (NH3(aq)), the color changes again to yellow

    so the same equilibrium dislocated again to the right:

    HIn H++In-
    Red               Yellow

  4. Doing this can be repeated endless.
    Every time the equilibrium will dislocate to the right of to the left.

    The overall situation in the beaker does only change a very littlebit.
    There is only a small dislocation of the equilibrium to one of the other side, dependent on the environment.