[Music] hi and welcome back to free science lessons by the end of this video you should be able to describe the oxidation of aldah you should then be able to describe how this reaction can be used to distinguish between alahh and ketones in the last video we looked at the structure of alahh and ketones and I've put a link to that video in the description below I'd recommend that you watch that video before you watch this one now a key reaction of aldhy is that they can be oxidized to form carboxilic acids I'm showing you here the oxidation of the aldhy ethanol forming ethanolic acid in this reaction the oxidizing agent is the acidified dichromate 6 ion this has the formula cr207 2h+ we can use either potassium D chromate and dilute sulfuric acid or we can use sodium dichromate and dilute sulfuric acid now the DI chromate ion has an orange color when the alahh is oxidized the DI chromate ion is reduced forming the chromium 3 ion which is green so during the reaction we see the color change from Orange to Green now alahh tides are relatively easy to oxidize so this reaction will take place even with gentle warming however in practice we reflux the alahh with excess oxidizing agent these conditions ensure that a as much of the aldhy is oxidized as possible at the end of the reaction we then use distillation to purify the carboxilic acid notice that in this equation the oxidizing agent is represented by the symbol capital O in square brackets and in the exam if you write an equation to show the oxidation of an alahh then you need to use that symbol now a key idea you need to remember is that ketones cannot be oxidized using acidified D chromate so if we're certain that we only have either an alahh or a ketone then we could use oxidation with acidified di chromate as a test for the alahh however there are much more reliable chemical tests that we'll see in later videos in the next video we look at the reduction of carbonal compounds which is an example of nucleophilic [Music] addition