Indicators pH-Dependent Colors

A FIGURE 16.10 MonRoring the pH during a Titration A pH meter monitors pH during titration. The inflection point in the resulting pH curve signifies the equivalence point. 

Titration of 0.100 M HC2H3O2 with 0.100 M NaOH. The endpoint of a titration is signaled by a color change in an appropriate indicator (in this case, phenolphthalein). 

Because its color is intense, only a small amonnt of indicator is required—an amount that will not affect the pH of the solntion or the equivalence point of the neutralization reaction. When the [HsO ] changes during the titration, the equilibrium shifts in response. At low pH, the [HsO ] is high and the equilibrinm lies far to the left, resulting in a solution of color 1. As the titration proceeds, the [H30 ] decreases, shifting the eqnilibrium to the 

The color of a solution containing an indicator depends on the relative concentrations of HIn and ln . As a nsefnl gnideline, we can assume the following  

From the Henderson-Hasselbalch eqnation, we can derive an expression for the ratio of [In-]/[HIn]  

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