Final answer:
The relationship between the pH range of an acid-base indicator and its pKa value is reflected in the color change interval of the indicator, typically about pKa ± 1. This indicates the transition from the protonated form of the indicator to its deprotonated form, which is also responsible for the observable color change in different pH conditions.
Step-by-step explanation:
The relationship between the pH range of an acid-base indicator and its pKa value is directly linked to the color change interval that the indicator exhibits. Acid-base indicators are weak acids or bases that exhibit different colors in their protonated and deprotonated forms. The pKa value of an indicator is a fundamental property that indicates the pH at which the concentrations of the protonated and deprotonated forms are equal.
When the pH is higher than the pKa, the solution contains more of the deprotonated form, which usually has a different color compared to the protonated form. Conversely, when the pH is lower than the pKa, the solution has a higher concentration of the protonated form. The pH interval during which the indicator changes color is typically about pKa ± 1. This range corresponds to the pH values over which there is a visible color change due to the changing concentrations of the protonated and deprotonated forms.
For titrations, it is important to select an indicator whose pKa value is close to the pH of the expected equivalence point. This is because a large change in pH at the equivalence point can cause the indicator to change color, denoting the end of the titration. Using an incorrect indicator can lead to significant errors, as it may change color before or after the equivalence point, depending on whether the titration involves a strong acid-base reaction or a weaker one.