Phenolphthalein changes from clear to pink near a pH of 8, but acids are exactly neutralized at a pH of 7. Does this discrepancy affect your results? Explain
Yes, this discrepancy could potentially affect the results when using phenolphthalein as an indicator to determine the endpoint of an acid-base titration.
When performing a titration, the goal is to neutralize the acid with a base, or vice versa. The point at which the acid and base completely react is called the equivalence point. At this point, the number of moles of acid is equal to the number of moles of base, resulting in a neutral solution with a pH of 7.
However, phenolphthalein changes color near a pH of 8, which is slightly alkaline. This means that when using phenolphthalein as an indicator, the endpoint of the titration (where the color change is observed) will occur slightly after the actual equivalence point is reached.
The consequence of this discrepancy is that the volume of base added to neutralize the acid will be slightly more than the actual stoichiometric requirement. This can lead to a slight overestimation of the concentration of the acid being titrated.
To minimize this discrepancy, other indicators that change color closer to a pH of 7, such as bromothymol blue or methyl orange, can be used. Additionally, using a pH meter or a more accurate indicator that changes color precisely at a pH of 7 can provide more accurate results.