Ocr chemistry alevel

You know hydrolysis of haloalkanes, do you mix it in water first - the haloalkane, get the halide ion and then go the experiment with agno3?

Reply 1

Hedwigeeeee

No, in this experiment u add dilute nitric acid first to make sure any other anions are removed and do not let these anions affect precipitation, then u just add agno3 aq to halogenalkane and u get agcl for example and observe the colour of precipitation to determine is the precipitation agcl agi or agbr, there is no need for hydrolysis.

Reply 2

Hedwigeeeee

or perhaps agno3 is already aq, so no need for extra water??

Reply 3

Pigster

If all you want to do is hydrolyse a haloalkane, you'd use NaOH(aq). Haloalkanes are usually pretty insoluble in water, so two layers will form. Enough haloalkane will dissolve to allow the reaction to occur. When the reaction occurs, an alcohol forms, which acts as a common solvent (dissolving both the OH- and the haloalkane).

But, if you want to use Ag+ to compare the rate of hydrolysis of different haloalkanes, then you can't use OH- as a brown sludge of Ag2O will form.

So, instead of using OH- as the nucleophile, we use water. Now water is a rubbish nucleophile compared to OH-, so we have to give it a little help - we add some alcohol at the start to act as the common solvent. We also add AgNO3(aq) - this supplies the Ag+ for the precipitation and the H2O which is the nucleophile.

i.e. your suggestion in your OP is incorrect.

For the record Hedwigeeeee is describing the use of Ag+ to detect halide ions in aqueous salts, but omitted the testing for SO42-, which needs to be done before testing for halide ions.