Boiling Point Indicates Ester Purity

Steps:

• Identify that food-grade esters require high purity for safety and flavor consistency.
• Recall that impurities alter a liquid's boiling behavior, making it a reliable purity test.
• Measure the boiling point of the ester sample under controlled conditions.
• Compare the observed value to the known boiling point of the pure ester; deviations signal impurities.

Why A is correct:

• Pure substances boil at a sharp, specific temperature; impurities cause boiling point depression and a broader range, as per Raoult's law on colligative properties.

Why the others are wrong:

• B. Colour: Pure esters are often colorless, and impurities may not visibly alter hue.
• C. Smell: Subjective and non-quantitative; impure esters may still smell similar.
• D. Solubility in water: Varies by ester type and is unaffected by minor impurities.

Final answer: A