4.5.1Unit 4. Rates, Equilibria and Further Organic Chemistry
Brønsted–Lowry Acid and Base Theory — IAL Edexcel Linear (Chemistry) Revision Notes & Topical Questions
5 min read 4 parts Lesson 34 of 56 Unit quiz
Curriculum Equation Key معادلة تفاعل تكوين الإستر (الأسترة) - Esterification Reaction EquationFast Exam Solution
R-COOH + R2-OH ⇌ (conc. H₂SO₄) R-COO-R2 + H₂O
Word Equation & Conditions: حمض كربوكسيلي + كحول (في وجود حمض الكبريتيك المركز كعامل حفاز ونازع للماء) ⇌ إستر + ماء
Location & Specifications: الكيمياء العضوية للثانوية العامة والتحصيلي و Edexcel Chemistry.
Part 1 of 4Acids and Bases
The theory describes acids and bases in terms of the transfer of a proton, H⁺.
Acid
- Acid A Brønsted–Lowry acid is a proton donor, such as HCl or CH₃COOH, which gives up H⁺ to another species.
Base
- Base A Brønsted–Lowry base is a proton acceptor, such as NH₃ or OH⁻, which uses a lone pair to bond to H⁺.
Proton transfer
- Proton transfer An acid only behaves as an acid when a base is present to accept the proton it donates.
In water
- In water The proton is accepted by water to form the oxonium ion, H₃O⁺, usually simplified to H⁺(aq).
Part 2 of 4Conjugate Pairs
Every acid–base reaction involves two pairs of species related by one proton.
Conjugate Pairs
Definition
- Definition A conjugate pair is an acid and its base, which differ by exactly one H⁺.
Example 1
- Example 1 In HCl + H₂O → H₃O⁺ + Cl⁻, HCl pairs with Cl⁻ and H₂O pairs with H₃O⁺.
Example 2
- Example 2 In NH₃ + H₂O ⇌ NH₄⁺ + OH⁻, NH₃ pairs with NH₄⁺ and H₂O pairs with OH⁻.
Amphoteric species
- Amphoteric species Water can act as an acid or a base, depending on what it reacts with.
| Acid | Conjugate base |
|---|---|
| HCl | Cl⁻ |
| CH₃COOH | CH₃COO⁻ |
| H₂O | OH⁻ |
| NH₄⁺ | NH₃ |
| H₂SO₄ | HSO₄⁻ |
Part 3 of 4Writing Equations
1
Identify the species that loses H⁺ and mark it as the acid, writing its conjugate base on the product side.
2
Identify the species that gains H⁺ and mark it as the base, writing its conjugate acid on the product side.
3
Use a single arrow for complete reactions of strong acids and a reversible arrow for weak acids and bases.
4
Check that atoms and charges balance on both sides of the equation.
Part 4 of 4Exam Checklist & Tips
4.5.1 – Key Points for the Exam
- Brønsted–Lowry acid Proton donor.
- Brønsted–Lowry base Proton acceptor.
- Conjugate pair An acid and base that differ by one H⁺.
- Amphoteric Able to act as both acid and base.
Common Mistakes
- Saying that a base is anything containing OH⁻; ammonia is a base without containing hydroxide.
- Writing a conjugate pair with a difference of more than one proton.
- Forgetting to label both pairs in an acid–base reaction.
- Giving the charge of the conjugate acid or base incorrectly.
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