CIE AS Chemistry (9701) exams from 2022

Revision Notes

1.7.8 Brønsted–Lowry Theory

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

Equilibria Brønsted-Lowry Acid_Base Definition, downloadable AS & A Level Chemistry revision notes

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

 

Equilibria Water as Brønsted -Lowry Acid, downloadable AS & A Level Chemistry revision notes

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

Equilibria Dot & Cross Diagram of Reaction between Water and Ammonia, downloadable AS & A Level Chemistry revision notes

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

Equilibria Water as Brønsted -Lowry Base, downloadable AS & A Level Chemistry revision notes

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

Equilibria Dot & Cross Diagram of Reaction between Water and Hydrochloric Acid, downloadable AS & A Level Chemistry revision notes

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

 

Equilibria Brønsted -Lowry Theory in Gaseous Reactions, downloadable AS & A Level Chemistry revision notes

Example of a Brønsted-Lowry acid and base reaction in the gas state

Exam Tip

An atom of hydrogen contains 1 proton, 1 electron and 0 neutrons. When hydrogen loses an electron to become H+ only a proton remains, which is why a H+ ion is also called a proton.

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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