2.3.2Inorganic Chemistry: Part 1
Acids, Bases and Protons — Edexcel International GCSE Science Double Award (Modular) - Chemistry Unit 1 Revision Notes & Topical Questions
5 min read 6 parts Lesson 11 of 15
Section 1 of 6Defining acids and bases by proton transfer
What a proton is
- What a proton is A hydrogen atom has one proton and one electron.
- When it loses its electron it becomes an H+ ion, which is just a single proton.
Acids
- Acids An acid is a proton donor: in water it ionises and releases H+ ions.
- The H+ ions are what make a solution acidic.
Bases and alkalis
- Bases and alkalis A base is a proton acceptor.
- An alkali is a soluble base.
- In solution it supplies OH− ions, which accept protons and make the solution alkaline.
Section 2 of 6Example ionisation equations
| Substance | Equation | Role |
|---|---|---|
| Hydrochloric acid | HCl(aq) → H+(aq) + Cl−(aq) | Proton donor |
| Sodium hydroxide | NaOH(s) → Na+(aq) + OH−(aq) | Provides OH−, a proton acceptor |
| Neutralisation | H+(aq) + OH−(aq) → H2O(l) | Proton transferred from acid to base |
Section 3 of 6From proton transfer to neutralisation
1Acid ionises
- Acid ionises The acid releases H+ ions into the solution.
2Alkali supplies OH−
- Alkali supplies OH− Hydroxide ions are present in the alkaline solution.
3Proton transfer
- Proton transfer Each OH− accepts an H+ from the acid.
4Water forms
- Water forms Water is made, and the acidity and alkalinity cancel out to give a neutral solution.
Section 4 of 6Applying the idea
1
Identify which species can release H+; that species is the acid.
2
Identify the species that receives the H+; that is the base.
3
Write the ionic equation for the transfer, showing the H+ moving from the donor to the acceptor.
4
Check the charges balance on both sides of the equation.
Section 5 of 6Key terms
| Term | Meaning |
|---|---|
| Proton | A positively charged particle in the nucleus; an H+ ion is a single proton. |
| Proton donor | A substance that gives away H+ ions; an acid. |
| Proton acceptor | A substance that takes H+ ions; a base. |
| Ionisation | The splitting of a molecule into ions when it dissolves in water. |
| Neutralisation | The reaction of H+ ions with OH− ions to make water. |
Section 6 of 6Exam technique
1
Saying an acid 'accepts' protons. Acids donate them and bases accept them.
2
Writing H+ as an atom that has no charge, or omitting charges from ionic equations.
3
Using the words base and alkali as exact synonyms. All alkalis are bases, but only soluble bases are alkalis.
4
Forgetting that the water produced in neutralisation is formed by H+ combining with OH−.
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