EDEXCEL IGCSE CHEMISTRY: DOUBLE SCIENCE 复习笔记:2.5.2 Acids, Alkalis & Neutralisation

EDEXCEL IGCSE CHEMISTRY: DOUBLE SCIENCE 复习笔记:2.5.2 Acids, Alkalis & Neutralisation

Acids & Alkalis


  • When acids are added to water, they form positively charged hydrogen ions (H+)
  • The presence of H+ ions is what makes a solution acidic
  • When alkalis are added to water, they form negative hydroxide ions (OH)
  • The presence of the OH ions is what makes the aqueous solution an alkali
  • The pH scale is a numerical scale which is used to show how acidic or alkaline a solution is, in other words it is a measure of the amount of the ions present in solution




  • A neutralisation reaction occurs when an acid reacts with an alkali
  • When these substances react together in a neutralisation reaction, the H+ ions react with the OH ions to produce water
  • For example, when hydrochloric acid is neutralised a sodium chloride and water are produced:


Equilibria Neutralisation Reaction of HCl and NaOH, downloadable AS & A Level Chemistry revision notes


  • The net ionic equation of all acid-base neutralisations and is what leads to a neutral solution, since water has a pH of 7:


H+  +  OH– ⟶ H2O

  • Neutralisation is very important in the treatment of soils to raise the pH as some crops cannot tolerate pH levels below 7
  • This is achieved by adding bases to the soil such as limestone and quicklime



Exam Tip

Not all reactions of acids are neutralisations. For example, when a metal reacts with an acid, although a salt is produced there is no water formed so it does not fit the definition of neutralisation.