IB Chemistry SL

Revision Notes

8.1.1 Brønsted–Lowry Acids & Bases

Brønsted–Lowry Acids & Bases

  • 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

  • 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 IB Chemistry revision notes

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

Worked Example

Identify the correct role of the species in the following reaction:

H2PO4(aq) + H2O(l) → HPO42−(aq) + H3O+(aq)

Bronsted Lowry Acids & Bases-Worked Example Question, downloadable IB Chemistry revision notes


The correct option is A.

    •  H2PO4is donating a proton to H2O, so H2PO4 must be an acid and H2O must be a base

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.


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