Amphiprotic Species (DP IB Chemistry): Revision Note

Philippa Platt

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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

Chemical equation showing water as a Brønsted-Lowry acid and ammonia as a base, forming hydroxide and ammonium ions.
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

Diagram showing water and ammonia reacting. Water donates H+ to ammonia. OH- is negatively charged, NH4+ is positively charged.
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

Chemical equation showing hydrochloric acid and water acting as a Brønsted-Lowry acid and base, forming chloride ion and hydronium ion.
The diagram shows water acting as a Brønsted-Lowry base by accepting a proton from hydrochloric acid proton using its lone pair of electrons

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

Diagram showing hydrochloric acid donating an H+ ion to water, resulting in chloride and hydronium ions. Arrows indicate electron movement.
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 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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Philippa Platt

Author: Philippa Platt

Expertise: Chemistry Content Creator

Philippa has worked as a GCSE and A level chemistry teacher and tutor for over thirteen years. She studied chemistry and sport science at Loughborough University graduating in 2007 having also completed her PGCE in science. Throughout her time as a teacher she was incharge of a boarding house for five years and coached many teams in a variety of sports. When not producing resources with the chemistry team, Philippa enjoys being active outside with her young family and is a very keen gardener

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