Chemistry: The Molecular Science (5th Edition)

Published by Cengage Learning
ISBN 10: 1285199049
ISBN 13: 978-1-28519-904-7

Chapter 15 - Additional Aqueous Equilibria - Questions for Review and Thought - Topical Questions - Page 693b: 36d

Answer

Phenolphthalein is the most suitable, because it changes its color in basic solutions, and the equivalence point of the titration between $KOH$ and $HNO_2$ is in basic solution.

Work Step by Step

$HNO_2$ is a weak acid and $KOH$ is a strong base; therefore, the pH at the equivalence point of their titration will be basic $(pH > 7)$. Analyzing the 3 given indicators on page 667, the one where the color changes in a basic solution is the most appropriate, so Phenolphthalein is the correct answer.
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