Question

In this experiment, you used phenolphthalein to monitor the neutralization reactions. describe the chemical differences between an equivalence point and an endpoint in titration and use this to explain whether phenolphthalein could be used as an indicator in any acid/base neutralization.

Answer 1

The endpoint in tiration is the point where an indicatior's halfway thru its color change. Equivalence point is where moles/stoichiometry of the system is satisfied (moles of reactants are equal to each other).

Titrating a strong acid with a strong base results in a salt that is neutral. Phenolphthalein changes color in the range 8.3 – 10. It is very easy to spot the change as it is colorless in acidic (< 8.3) and pink in basic (> 10).

pH will rapidly change near titration equivalence point. Only one drop of the titrant causes this large change, the color change of phenolphthalein does not occur on the equivalence point, but IT IS within about 1 drop. It would be considered an "acceptable uncertainty" in using titration to determine concentration by volumetric measurement.