Question

When $CH_3COOCH_3 + HCl$ is titrated with $NaOH$ then at neutral point the colour of phenolphthalein becomes colourless from pink due to

• A. formation of $CH_3OH$
• B. formation of $CH_3COOH$ which acts as a weak acid
• C. phenolphthalein vaporizes
• D. presence of $HCl$

Answer 1

Answer: (B)

$NaOH$ solution is taken in a conical flask with phenolphthalein indicator (pink colour) and $CH_3COOCH_3 + HCl$ solution is added from burette slowly.
First, $HCl$ left after hydrolysis of ester (being a strong acid) gets consumed then $CH_3COOH$ being a weak acid will bring the titration to the neutralisation point.
$CH_3COOCH_3 \xrightarrow[H^+]{ H_2O} CH_3COOH + CH_3OH$
$HCl + NaOH \rightarrow NaCl + H_2O$
$CH_3COOH + NaOH \rightarrow CH_3COONa $