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

Lewis diagram for the reaction between water and ammonia

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

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 Summary
Amphiprotic:
Can both accept and donate a proton (H⁺)
Amphiprotic substances act as both a proton donor and acceptor
All amphiprotic substances are also amphoteric
Amphoteric:
Can act as both an acid and a base
Amphoteric substances can behave as acids or bases in a chemical reaction
Not all amphoteric substances are amphiprotic
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