Final answer:
If too much base is added in an acid-base titration, a proton is lost from the acid indicator to form its conjugate base, resulting in the solution taking on the color of the conjugate base. Phenolphthalein indicator, for instance, would turn a vivid pink indicating excess base.
Step-by-step explanation:
If the acid was titrated with too much base (titrated past the initial end point), a proton (H+) is lost to yield its conjugate base (In−). This gives the resulting solution a color characteristic of the conjugate base.
During an acid-base titration, the goal is to neutralize the acid with a base until the equivalence point is reached, which is typically indicated by a color change due to a pre-added indicator. If an excess of base is added, exceeding the end point, the indicator's color will reflect the excess base present. For example, when using phenolphthalein as the indicator, at the equivalence point the solution will turn a faint pink color. If the titration continues past this point, the pink may become more intense and vivid, indicating an excess of base.
It is essential to add the titrant slowly to accurately determine the point of color change. The selection of an appropriate indicator, such as methyl orange, litmus, or phenolphthalein, depends on the specific type of titration and the pH change interval of the titration curve.