Question

The amount of indicator used in an acid-base titration must be small. Why?

Short answer

In an acid-base titration, the amount of indicator must be small to minimize its interference with the reaction while still providing a clear, observable signal of when the titration has reached its equivalence point.

Step-by-step solution

Understand the role of the indicator

An indicator is used in a titration to signal the point at which the reaction has reached its equivalence point, that is, when the moles of acid equal the moles of base. This is typically shown by a change in color. Since its role is primarily as a signal, only a small amount is required.

Discuss the behavior of an indicator

Indicators are weak acids or bases themselves and they can momentarily affect the pH of the solution when added. This deviation could affect the accuracy of the titration, but, given the minute quantities of the indicator used, this influence is negligible.

Conclude

Therefore, only a small amount of indicator is used in an acid-base titration to minimize the interference of the indicator with the reaction while still providing a clear, observable signal of when the titration has reached its equivalence point.