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Chapter 17: Problem 21

Explain how an acid-base indicator works in a titration.

Short Answer

Expert verified
An acid-base indicator changes its color with changes in pH and it is used in titration to visually indicate when the endpoint (the point of neutralization) is reached. Its chemical nature allows it to change color when the pH shifts in the solution.

Step by step solution

01

Understanding Acid-Base Indicators

Acid-base indicators are substances that change their color in response to changes in pH, which is a measure of the acidity or basicity of a solution. Examples of such indicators include litmus paper (which turns red in acidic solutions and blue in basic solutions) and phenolphthalein (which is colorless in acidic solution and pink in a basic solution).
02

Understanding Titration

Titration is a quantitative chemical analysis method used to determine the concentration of an unknown solution (analyte) by slowly adding a solution of known concentration (titrant) until reaction between them is complete. The point where the reaction is complete is known as the endpoint.
03

Role of an Indicator in Titration

The role of an indicator in a titration is to show visually when the endpoint has been reached. This is achieved by the change in color of the indicator. At the beginning of the titration, drops of indicator are added to the analyte. As the titrant is added, the reaction proceeds and the pH of the solution changes. When the endpoint is reached, the pH changes rapidly over a very small volume of added titrant and this causes the indicator to change its color.
04

Indicator and Endpoint

The choice of an indicator for a given titration depends on the characteristics of the acid and base being titrated. The indicator is chosen such that its pH range (the pH at which it changes color) falls within the rapid pH change associated with the end point of the titration reaction. Once the color change is observed, the volume of titrant added is noted. This is used to calculate the concentration of the analyte, completing the titration process.

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Most popular questions from this chapter

Write the solubility product expression for the ionic compound \(\mathrm{A}_{x} \mathrm{~B}_{y}\).

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