Question

Potassium hydrogen phthalate (KHP) concentrations can be determined through titrating samples of KHP (a monoprotic acid) with bases such as NaOH in the presence of an indicator such as phenolphthalein. The indicator is colorless in an acidic solution and turns pink in an alkaline solution. Thus, we can establish an equilibrium for the phenolphthalein with the following reaction.

HIn + H₂O ---> In⁻ + H₃O⁺

If the Hin species is "acid color" or colorless for the phenolphthalein, and the In species is "base color" or pink for this particular indicator, what color will appear in a flask in which a 0.2993 gram sample of KHP is completely neutralized with an excess of NaOH?
A. The flask will be colorless.
B. The flask will be pink.
C. The flask will be white from KCI precipitation.
D. There is insufficient information to solve this problem.

Answer 1

In a titration using phenolphthalein as an indicator, when KHP is completely neutralized by NaOH, the solution will turn pink, indicating the presence of an alkaline environment. Option B is the correct answer.

Step-by-step explanation:

When determining potassium hydrogen phthalate (KHP) concentrations through titration with NaOH, an acid-base indicator such as phenolphthalein is used. Phenolphthalein changes color based on the pH of the solution: it's colorless in acidic environments and turns pink in alkaline solutions.

In the context of the question, when a 0.2993 gram sample of KHP is completely neutralized with an excess of NaOH, the solution in the flask will become slightly alkaline. Since phenolphthalein turns pink in alkaline solutions, specifically at a pH higher than 8.3, the flask will show a pink color after the titration, indicating that the sample of KHP has been neutralized.

The correct option is B. The flask will be pink.