Chapter U6.123, Problem 1TAI

Interpretation Introduction

Interpretation: Acid-base indicators work needs to be explained.

Concept Introduction: Acid-base indicators are substances that respond to a change in the ${\text{H}}^{+}$ ion concentration of a solution. Acid-base indicators are usually weak acids, or weak bases. A weak acid is a compound that partly dissociates in solution, or breaks apart.

Answer to Problem 1TAI

Depending on pH of the solution acid-base indicator changes color.

Explanation of Solution

Acid-base indicators are weak acids or bases that change color depending on pH. The concentrations of an indicator molecule and its anion depend on the concentration of ${\text{H}}^{+}$ ions in solution. Therefore, the color of an indicator is a measure of acidity of the solution. The color of an indicator changes when the concentrations of the HIn molecules and ${\text{In}}^{-}$ anions are identical. This occurs when $\text{K = }\left[{\text{H}}^{+}\right]$ .

Conclusion

In an aqueous solution, a weak base or weak acid shows a color change as the concentration of ${\text{H}}^{+}$ and ${\text{OH}}^{-}$ ions changes.