Amphiprotic Species (DP IB Chemistry): Revision Note

Amphiprotic Species

• Species that can act both as proton donors and acceptors are called amphiprotic

Water as a Brønsted-Lowry acid

Diagram to show how water is amphiprotic

The diagram shows water acting as a Brønsted-Lowry acid by donating a proton to ammonia which accepts the proton using its lone pair of electrons

Lewis diagram for the reaction between water and ammonia

The Lewis diagram for the reaction of water with ammonia to show how water acts as a Brønsted-Lowry acid and ammonia as a Brønsted-Lowry base

Water as a Brønsted-Lowry base

Diagram to show how water is amphiprotic

The diagram shows water acting as a Brønsted-Lowry base by accepting a proton from hydrochloric acid proton using its lone pair of electrons

Lewis diagram for the reaction between water and hydrochloric acid

The Lewis diagram for the reaction of water with hydrochloric acid to show how water acts as a Brønsted-Lowry base and ammonia as a Brønsted-Lowry acid

What is the difference between amphiprotic and amphoteric?

• A compound that is amphoteric means it has both basic and acidic character

  • When the compound reacts with an acid, it shows that it has basic character

  • When it reacts with a base, it shows that it's acidic

  • An example of this is aluminium oxide which reacts with both hydrochloric acid and sodium hydroxide:

Al₂O₃ (s) + 6HCl (aq) → 2AlCl₃ (aq) + 3H₂O (l)

Al₂O₃ (s) + 2NaOH (aq) + 3H₂O (l) → 2NaAl(OH)₄ (aq)       

• When a compound is amphiprotic, it means it can act as a proton donor and as a proton acceptor

• Aluminium oxide is not amphiprotic, even though it is amphoteric

Amphiprotic versus Amphoteric Table