[Cleofe_g]

When conducting a titration, do you need to keep the number of indicator drops constant? For my titration practical, I'm titrating a known concentration of diluted NaOH solution with four different unknown concentrations of acid from different pineapple juices. I tried adding 3 drops of phenolphthalein indicator to each sample of pineapple juice but it's difficult to determine the end point with 3 of the pineapple juice samples due to their darker colour.

[sjb]

it would make sense, after all the indicator is also (typically in these cases) either an acid or a base as well so you may need less or more titrant to complete the reaction.

[Borek]

http://www.titrations.info/acid-base-titration-indicators

In short: using different amount of one color indicator (like phenolphthalein) for different titrations can lead to additional errors. This problem is not present when using two color indicators (like methyl orange). Amount of indicator is typically several orders of magnitude lower than amount of the acid/base in the sample, so it can be usually ignored.