Question

A student determines the acetic acid concentration of a sample of distilled vinegar by titration of 25.00 mL of the vinegar with standardized sodium hydroxide solution using phenolphthalein as an indicator. Which error will give an acetic acid content for the vinegar that is too low? (A) Some of the vinegar is spilled when being transferred from the volumetric flask to the titration flask. (B) The NaOH solution is allowed to stand for a prolonged period after standardization and absorbs carbon dioxide from the air. (C) The endpoint is recorded when the solution turns dark red instead of faint pink. (D) The vinegar is diluted with distilled water in the titration flask before the NaOH solution is added

The answer is A. HOW???

Answer 1

This is a volumetric titration, where volume measurement plays a key role in the titration. In this titration a standard solution is prepared taking the titrant with the known volume and concentration which has to react against the analyte to determine concentration. Hence loss of the volume will give wrong value of the concentration.

Hence the student may get too low value of acetic acid may be due to the titration of less volume of vinegar. Hence the correct answer will be (A) Some of the vinegar is spilled when being transferred from the volumetric flask to the titration flask.