Final answer:
A back titration differs from a regular titration by adding an excess of standard reagent to the analyte and then titrating the remaining excess, rather than adding the titrant directly to the analyte until the equivalence point is reached. Indicators, like phenolphthalein, still signal when the equivalence point is achieved.
Step-by-step explanation:
The primary difference between back titration and a regular titration is in the way the equivalence point is reached. In a regular titration, the titrant is added directly to the analyte until the reaction reaches the equivalence point, which is often detected by a color change of an indicator. In back titration, an excess of a standard reagent is added to the analyte, and the remaining excess reagent is then titrated. This approach may be used when the analyte is not soluble, reacts very slowly with the titrant, or when the direct titration has no suitable indicator.
Indicators are crucial in both back titration and regular titration as they signify the achievement of the equivalence point through a change in color. Phenolphthalein, for example, is a common indicator that turns from colorless to pink at the equivalence point in strong acid-strong base titrations. The reaction itself does not occur in reverse, a burette is still often used to add the titrant, and reagents can be colorless or colored depending on the type of titration and the indicator being used.