Brønsted–Lowry Theory (Cambridge (CIE) AS Chemistry): Revision Note

Brønsted–Lowry Theory

• The Brønsted-Lowry Theory defines acids and bases in terms of proton transfer between chemical compounds

• A Brønsted-Lowry acid is a species that gives away a proton (H⁺)

• A Brønsted-Lowry base is a species that accepts a proton (H⁺) using its lone pair of electrons

How an acid acts as a Brønsted-Lowry proton donor

The diagram shows a Brønsted-Lowry acid which donates the proton to the Brønsted-Lowry base that accepts the proton using its lone pair of electrons

• Species that can act both as acids and bases are called amphoteric

  • Eg. water as a Brønsted-Lowry acid

Water acting as a Brønsted-Lowry acid

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

Dot and cross diagram showing the Brønsted-Lowry behaviour of water with ammonia

The diagram shows a dot & cross 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

• Eg. water as a Brønsted-Lowry base

Water acting as a Brønsted-Lowry base

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

Dot and cross diagram showing the Brønsted-Lowry behaviour of water with hydrochloric acid

The diagram shows a dot & cross 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

• The Brønsted-Lowry Theory is not limited to aqueous solutions only and can also be applied to reactions that occur in the gas phase

A Brønsted-Lowry acid and base reaction

HCl acts as a Brønsted-Lowry acid by donating a proton while ammonia acts as a Brønsted-Lowry base by accepting a proton