4.6.2Electrochemistry
Reactions of Carboxylic Acids — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions
5 min read 4 parts Lesson 12 of 20 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 5Typical Acid Reactions
Metals
- Metals Carboxylic acids react with reactive metals such as magnesium to form a salt and hydrogen gas.
Carbonates
- Carbonates Carboxylic acids react with carbonates to form a salt, water and carbon dioxide, which causes fizzing.
Bases
- Bases Carboxylic acids react with bases such as sodium hydroxide to form a salt and water in a neutralisation reaction.
Salt names
- Salt names Salts are named by replacing -oic acid with -oate, so ethanoic acid forms ethanoates and butanoic acid forms butanoates.
Limewater test
- Limewater test The carbon dioxide released in the carbonate reaction turns limewater milky, which is a test for the gas.
Part 2 of 5Equations
1
Ethanoic acid reacts with magnesium, forming magnesium ethanoate and hydrogen: 2CH₃COOH + Mg → (CH₃COO)₂Mg + H₂.
2
Ethanoic acid reacts with sodium hydroxide, forming sodium ethanoate and water: CH₃COOH + NaOH → CH₃COONa + H₂O.
3
Butanoic acid reacts with potassium carbonate, forming potassium butanoate, water and carbon dioxide: 2CH₃CH₂CH₂COOH + K₂CO₃ → 2CH₃CH₂CH₂COOK + H₂O + CO₂.
Part 3 of 5Products Summary
Products Summary
Metal reaction
- Metal reaction Hydrogen is the gas produced when a metal reacts with a carboxylic acid.
Carbonate reaction
- Carbonate reaction Carbon dioxide and water are produced along with the salt in a carbonate reaction.
Salt ion count
- Salt ion count Magnesium needs two ethanoate ions, so the formula of the salt is (CH₃COO)₂Mg.
| Acid and reactant | Salt formed | Other product or products |
|---|---|---|
| Ethanoic acid + magnesium | Magnesium ethanoate | Hydrogen |
| Ethanoic acid + sodium hydroxide | Sodium ethanoate | Water |
| Butanoic acid + potassium carbonate | Potassium butanoate | Water and carbon dioxide |
Part 4 of 5Worked Example
Question Write a word equation and a balanced symbol equation for the reaction of propanoic acid with sodium carbonate, and name the salt and gases formed.
- Word equationpropanoic acid + sodium carbonate → sodium propanoate + water + carbon dioxide
- Symbol equation2C₂H₅COOH + Na₂CO₃ → 2C₂H₅COONa + H₂O + CO₂
- Check
- C 7 = 7;
- H 12 = 10 + 2;
- O 7 = 4 + 1 + 2;
- Na 2 = 2
- C 7 = 7;
Answer
- Sodium propanoate is the salt, and carbon dioxide is the gas (with water formed).
- Symbol equation: 2C₂H₅COOH + Na₂CO₃ → 2C₂H₅COONa + H₂O + CO₂.
Part 5 of 5Exam Checklist & Tips
4.6.2 – Key Points for the Exam
- Salt A compound formed when the hydrogen of an acid is replaced by a metal or ammonium ion.
- Neutralisation A reaction between an acid and a base that forms a salt and water.
- Effervescence Fizzing caused by the release of a gas, such as carbon dioxide.
- Limewater Calcium hydroxide solution, which turns milky in the presence of carbon dioxide.
- Carbonate A compound containing the CO₃²⁻ ion.
Common Mistakes
- Writing the salt name as propanate; salts of carboxylic acids end in -oate.
- Forgetting water and carbon dioxide among the products of the carbonate reaction.
- Writing the magnesium salt as CH₃COOMg, which does not balance; it must be (CH₃COO)₂Mg.
- Stating that carbon dioxide is produced when a carboxylic acid reacts with a metal.
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