Rank the following species in order of increasing acidity (weak to strong) H2SO4, NH3, H20, CH3OH, CH3COOH, HF, H30^+.  Also explain the hierarchy of rules to why they are in the specific order.

Expert Answers
ncchemist eNotes educator| Certified Educator

Let's look at each one individually and then determine the order.

Sulfuric acid (H2SO4): This is a classic strong mineral acid.  It completely ionizes in water and is a very strong acid.

Ammonia (NH3):  This is actually a base.  Under extremely basic conditions it could function as an acid and lose a proton, but generally it is considered a weak base (it accepts protons).

Water (H2O):  This is completely neutral.  Not really an acid or a base.

Methanol (CH3OH):  This is a very weak acid.  The hydroxyl hydrogen can deprotonate, especially in the presence of a base, but generally this is a very weak acid.

Acetic acid (CH3COOH): This is a weak acid.  Acetic acid is the active ingredient in vinegar.  The carboxylic acid proton will dissociate in water but not completely.

Hydrofluoric acid (HF):  This is also a strong mineral acid.  However it is not quite as strong as the rest since it does not completely dissociate in water.  Actually this one is a bit complicated since its acidic strength does depend on its concentration, but we'll go with strong but not among the strongest.

Hydronium ion (H3O+):  This is the ultimate acid but it cannot exist on its own in reality without a counterion.  The hydronium ion is a proton coordinated in solution with a water molecule.  Since a proton is the ultimate acid this would be the ultimate acid since there is no counterion to interact with it.

So the final ranking from weakest to strongest is: NH3, H2O, CH3OH, CH3COOH, HF, H2SO4, H3O+.