Bases (Edexcel IGCSE Chemistry (Modular))

Revision Note

Test yourself
Stewart Hird

Written by: Stewart Hird

Reviewed by: Lucy Kirkham

Bases

What makes a base act like a base?

  • Bases are substances which can neutralise an acid, forming a salt and water

  • The term base and alkali are not the same

  • A base which is water-soluble is referred to as an alkali

    • So, all alkalis are bases, but not all bases are alkalis

  • Alkalis have pH values of above 7

  • In basic (alkaline) conditions red litmus paper turns blue

  • Bases are usually oxides, hydroxides or carbonates of metals

  • The presence of the OH- ions is what makes the aqueous solution an alkali

  • One unusual base is ammonia solution

    • When ammonia reacts with water it produces hydroxide ions

Some common alkalis and the ions they contain

Name of alkali

Formula

Ions formed in water

Sodium hydroxide

NaOH

Na+ + OH-

Potassium hydroxide

KOH

K+ + OH-

Aqueous ammonia

NH3 (+ H2O)

NH4+ + OH-

Examiner Tips and Tricks

Aqueous ammonia and ammonium hydroxide are the same thing. When ammonia gas dissolves in water it forms ammonium hydroxide. Be careful to use the correct terminology: ammonia is the gas, NH3, ammonium is the ion present in ammonium compounds, NH4+

Last updated:

You've read 0 of your 10 free revision notes

Unlock more, it's free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Stewart Hird

Author: Stewart Hird

Expertise: Chemistry Lead

Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Topic Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.

Lucy Kirkham

Author: Lucy Kirkham

Expertise: Head of STEM

Lucy has been a passionate Maths teacher for over 12 years, teaching maths across the UK and abroad helping to engage, interest and develop confidence in the subject at all levels.Working as a Head of Department and then Director of Maths, Lucy has advised schools and academy trusts in both Scotland and the East Midlands, where her role was to support and coach teachers to improve Maths teaching for all.