Transition elements
Read our general notes on Risk Assessment
Why is FeCl3 solution not neutral
and why it will not work if the solution is alkaline or acidic?
In solution the iron(III) ions are hydrated: Fe(H2O)63+(aq).
The iron(III) ion - like the aluminium(III) ion - has a strong tendency to polarise neighbouring ions and mole=cules. Its polarising power is high because it is highly charged (3+) and relatively small. The effect on the ligand water molecules in the hydrated ion is to make them more acidic than free water molecules. As a result the hydrated iron(III) ion is about as strong an acid as ethanoic acid.
A solution of ion(III) ions has to be neutral for some tests - such as the test for phenols. In this test the iron(III) form a violet complex with the phenate ion. The test does not work if the solution is too acidic because phenol is a weak acid and so there is very little phenate ion present is the pH is too low.
The test does not work under alklaine conditions because the iron(III) precipitates as the hydroxide.
Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website.
For further guidance see our tutorial on Risk Assessment.
Rate this page or react
Share your views on this page, 0 ratings so far
updated: 20 April 2004
