CIE AS Chemistry (9701) exams from 2022

Revision Notes

1.7.7 Acids & Bases

Common Acids

  • An acid is a substance that neutralises a base forming a salt and water:

2HCl(aq) + CaO(s) ⇌ CaCl2(aq) + H2O(l)

acid                                salt


Equilibria Acid Base Reaction, downloadable AS & A Level Chemistry revision notes

Acids react with bases to form salt and water

  • Acids are also substances that release hydrogen ions when they dissolve in water:

HCl(g) → H+(aq) + Cl(aq)


Equilibria Acid Dissociation, downloadable AS & A Level Chemistry revision notes

Acids dissociate in water to release a hydrogen ion

Names & formulae of some common acids table

Equilibria Table 1_Common Acids, downloadable AS & A Level Chemistry revision notes

  • In organic acids (such as carboxylic acids) only some of the hydrogen atoms can form ions when the acid dissociates

Common Alkalis

  • A base is a compound that neutralises an acid forming a salt and water

2HCl(aq) + CaO(s) ⇌ CaCl2(aq) + H2O(l)

 base          salt

  • A base is a substance that accepts hydrogen ions or a compound that contains oxide or hydroxide ions
    For example:

NH3(g) + H2O(l) → NH4+(aq) + OH(aq)

base                                hydroxide ions

For example:

NaOH(s) + aq → Na+(aq) + OH(aq)

base                                hydroxide ions

  • A base that is soluble in water is called an alkali

Names & formulae of some common alkalis table

Equilibria Table 1_Common Alkalis, downloadable AS & A Level Chemistry revision notes

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.

Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now
Already a member?
Go to Top