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Test for ethanoic acid [UK] 

May 10, 2007

Hello :)

I am an AS Chemistry Student, and Have a planning exercise. I have to identify 6 liquids. I've almost completed the exercise but have become stuck! Ahh!

I've been looking for a positive test for ETHANOIC Acid. My original plan was to add a sample of Iron (3) chloride to all liquids, and identify by colour change! But I cannot find a suitible equation to show this!

Does anyone know of the reaction between ethanoic acis and Iorn (3) Chloride, or of a another postive test for Ethanoic acid?!

Thanks for your times, guys!

Natalie John
A- Level Chemistry Student - Swansea, Wales, UK

The easiest method is smell - ethanoic acid (known as acetic acid in the USA) has a characteristic sharp vinegar smell.

The Yahoo answer re ferric chloride as indicator may be wrong: The method works for the salts of the acid, but the color disappears in the acidic solution itself.

If you have access to an IR spectrophotometer, acetic acid has a well-known spectrum. The C=O bond gives an absorption peak at 1680-1750 cm(-1) and the O-H bond gives a broad trough in the range 2500-3300 cm(-1). http://www.chemguide.co.uk/analysis/ir/interpret.html

Reaction of acetic acid with an alcohol will produce an ester (typically, sweet smelling). E.g., reaction with ethyl alcohol (with sulfuric acid present as catalyst and a desiccant to remove water produced) produces ethyl acetate, which is commonly found in nail polish remover and has a fruity smell.

As a weak acid, its solution conductivity is lower & pH is higher than a strong acid of equal concentration. Titration with 1 N NaOH solution should produce a characteristic curve (pH vs. volume titrant).
Reaction with Mg metal will produce H2 gas, and reaction with baking soda will give CO2 gas [true for most acids]. Wikipedia gives many properties which may be useful.
http://en.wikipedia.org/wiki/Acetic_acid#Detection

Ken Vlach - Goleta, California