Acids, Alkalis & Neutralisation (Edexcel IGCSE Chemistry: Double Science)
Revision Note
Author
StewartExpertise
Chemistry Lead
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
Neutralisation
- 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:
- 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.
You've read 0 of your 0 free revision notes
Get unlimited access
to absolutely everything:
- Downloadable PDFs
- Unlimited Revision Notes
- Topic Questions
- Past Papers
- Model Answers
- Videos (Maths and Science)
Did this page help you?