Chapter 16, Problem 38A

Interpretation Introduction

Interpretation:

Using a chemical equation, the working principle of an indicatorhave to be explained.

Concept Introduction:

An indicator is a chemical compound which indicates the color change depending on the concentration of hydrogen ions in a solution. In general, an indicator displays different color in acidic and basic solution.

Answer to Problem 38A

An indicator is a chemical compound which indicates the color change depending on the concentration of hydrogen ions in a solution. Chemists often use the indicator to detect the equivalence point of an acid-base titration. An indicator exhibits two different colors in two different pH medium (acidic and basic). Indicator can work in a broad range of pH.

Let’s assume an indicator HIn which is a weak acid. This weak acid HIn is in equilibrium with H+ and In- ions. The color of HIn is red and color of the anionic form In- is blue.

  $\mathrm{HIn}\rightleftharpoons H^{+}+I{n}^{-}$

In acidic medium, theequilibrium shifts to the left side and the concentration of HIn becomes predominant, so the solution exhibits red color.

  $\mathrm{HIn}\rightleftharpoons H^{+}+I{n}^{-}$

In basic medium, theequilibrium shifts to the right side and the concentration of H+decreases. The concentration of In- becomes predominant thus the solution exhibits, blue color.

Explanation of Solution

An indicator is a chemical compound which indicates the color change depending on the concentration of hydrogen ions in a solution. Chemists often use the indicator to detect the equivalence point of an acid-base titration. An indicator exhibits two different colors in two different pH medium (acidic and basic). Indicator can work in a broad range of pH.

  $\mathrm{HIn}\rightleftharpoons H^{+}+I{n}^{-}$

Let’s assume an indicator HIn which is a weak acid. This weak acid HIn is in equilibrium with H+ and In- ions. The color of HIn is red and color of the anionic form In- is blue.

  $\mathrm{HIn}\rightleftharpoons H^{+}+I{n}^{-}$

In acidic mediumtheequilibrium shifted to the left side and the concentration of HIn becomespredominant, so the solution exhibited red color.

  $\mathrm{HIn}\rightleftharpoons H^{+}+I{n}^{-}$

In basic medium theequilibrium shifted to the right side and the concentration of H+decreases. The concentration of In- becomes predominant thus the solution exhibited blue color.

  $\mathrm{HIn}\rightleftharpoons H^{+}+I{n}^{-}$