Mammoth Memory

For A-Level students or crazy people

In simple terms, an acid is a compound that has dissolved in water and has a pH of less than 7.

For A-Level…

You need to know that an acid is a compound that has dissolved in water and donated a hydrogen proton. This hydrogen proton combines with a water molecule, while the electron is released and able to roam freely. As a result, the acid will carry an electric charge.

A hydrogen atom consists of only a proton and an electron.

Hydrogen has one electron negatively charged and one proton positively charged


If the electron is released to roam around in a solution, only a hydrogen proton is left. This hydrogen proton is positively charged and called an ion or, more precisely, a cation.

This hydrogen proton of H+ cation cannot exist on its own, so latches itself onto the water in the solution.



This is why at A-Level definitions proceed as follows:

  • An acid is any substance that has donated a hydrogen proton to water
  • A base is any substance that will accept a hydrogen proton from water
  • An alkali is a base that has dissolved in water
  • A salt is a compound that is created by the reaction between an acid and a base (or alkali).
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