There are two chemical tests that will give a positive test for an aldehyde but not a ketone.įehling’s solution (a mixture of solutions of copper sulphate and sodium hydroxide) is a blue solution which when gently heated with an aldehyde forms a red precipitate of copper(I) oxide. The A Level syllabus requires candidates to be able to carry out a chemical test to distinguish an aldehyde from a ketone. It is very important that any unreacted hydroxide ions are removed completely to give a neutral or acidic solution as silver hydroxide will also produce a precipitate. Chloride ions will produce a white precipitate, bromide a cream precipitate and iodide produces a yellow precipitate. The halide ions can be detected using nitric acid followed by silver nitrate. Gentle heating will produce an alcohol and liberate halide ions. A small quantity of ethanol is also required to dissolve the haloalkane.

The presence of a halogenoalkane (except fluoroalkanes) can be confirmed by first carrying out a nucleophilic substitution reaction with aqueous sodium hydroxide solution. Effervescence will indicate the production of a gas and bubbling it through limewater will confirm that the gas is carbon dioxide. Sodium carbonate is as good a choice as any. Test for carboxylic acidsĬarboxylic acids will react with metal carbonates to produce a salt, water and carbon dioxide. Bromine water is orange but the halogenoalkane formed will be colourless.

Test for alkenesĪlkenes will react with bromine water to form a halogenoalkane. Mechanisms for some of the reactions listed below can be found here. If you have not already done so, you should read my previous post and ensure that you are familiar with the chemical tests listed here. In this blog post I summarise all the organic tests required for A Level Chemistry.

Aldehyde functional group