Describe the strength of organic acids relative to chloro substituted acids

Describe the strength of organic acids relative to chloro substituted acids


1 Answers

Aman Bansal
592 Points
12 years ago

Dear Aisha,

Organic acids as weak acids

For the purposes of this topic, we are going to take the definition of an acid as "a substance which donates hydrogen ions (protons) to other things". We are going to get a measure of this by looking at how easily the acids release hydrogen ions to water molecules when they are in solution in water.

An acid in solution sets up this equilibrium:



Note:  We are writing the acid as AH rather than HA, because, in all the cases we shall be looking at, the hydrogen we are interested in is at the right-hand end of a molecule.


A hydroxonium ion is formed together with the anion (negative ion) from the acid.

This equilibrium is sometimes simplified by leaving out the water to emphasise the ionisation of the acid.

If you write it like this, you must include the state symbols - "(aq)". Writing H+(aq) implies that the hydrogen ion is attached to a water molecule as H3O+. Hydrogen ions are always attached to something during chemical reactions.

The organic acids are weak in the sense that this ionisation is very incomplete. At any one time, most of the acid will be present in the solution as un-ionised molecules. For example, in the case of dilute ethanoic acid, the solution contains about 99% of ethanoic acid molecules - at any instant, only about 1% have actually ionised. The position of equilibrium therefore lies well to the left.

Best Of Luck...!!!!

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Aman Bansal

Askiitian Expert

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