Question

You're given 4 vials, each vial contains a chemical (a ketone, an ester, an aldehyde and...

You're given 4 vials, each vial contains a chemical (a ketone, an ester, an aldehyde and a carboxylic acid). You're also given reagents: aqueous NaHCO3, Tollen's Reagent, and 2,4-dinitrophenlylhydrazine.

Describe how you could determine which chemical is in each vial.

Homework Answers

Answer #1

Once the presence of carbonyl group has been identified using 2,4-dinitrophenylhydrazine (also known asBrady's reagent or 2,4-DNPH), Tollens' reagent can be used to distinguish ketone vsaldehyde. Tollens' reagent gives a negative test for most ketones, except those withalpha-hydroxy ketone.

A few drops or a few crystals of the unknown sample are dissolved in 1mL of methanol and slowly added to 1 mL of a saturated solution of sodium bicarbonate. Evolution of a carbon dioxide gas is a positive test for the presence of the carboxylic acid and certain phenols listed in the Complications section.

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