Lesson 5: Carboxylic Acids & Amines: Acid-Base Properties
Demonstrating understanding of organic chemical structure, properties, and reactions for NCEA Level 2 Chemistry.
🎯 Ngā Whāinga Akoranga | Learning Intentions
Carboxylic acids (-COOH) as weak organic acids (turn blue litmus red, react with carbonates to produce CO2 gas) and amines (-NH2) as weak organic bases (turn red litmus blue, fishy odour, accept protons).
Write acid-base neutralization equations, predict solubility trends (short-chain vs long-chain), and perform diagnostic tests with litmus paper and NaHCO3.
🎥 Media Anchor & Pedagogical Scaffold
Carboxylic Acids and Amines Chemistry
Video Clip: Alcohols, Carboxylic Acids and Esters — everything you need to know | GCSE & IGCSE Chemistry (Science with Hazel) (Runtime: 9m 52s).
🧠 1. Before Viewing (Activate & Predict)
Why do vinegar (ethanoic acid) and fish odour (methylamine) exhibit contrasting acidic and basic properties?
👁️ 2. During Viewing (Watch With a Job)
- Carboxylic acid structure: draw the -COOH functional group. Why does this group make carboxylic acids acidic? (What does it donate?)
- Ester formation: write the word equation for the reaction between a carboxylic acid and an alcohol. What type of reaction is this, and what are the two products?
- Acid strength: are carboxylic acids strong or weak acids? How do you know? (What happens when you dissolve one in water?)
🗣️ 3. After Viewing & Kaiako Move (Process & Apply)
Kaiako Move: Connect short-chain carboxylic acids to traditional food preservation (pickling/fermentation) and amines to natural breakdown products.
Immediate Task: Complete Section 5 of your Organic Portfolio: Acid-Base Diagnostic Flowchart & Litmus Test Record.
⚡ Whakaoho | Do Now: Organic Recall Challenge (10 mins)
Why lemon on fish works. The smell of old fish is amines evaporating off the surface. Squeeze lemon juice on it and the smell drops away.
Two minutes: amines are weak bases and lemon juice is an acid. Say what reaction happens, then explain the part that actually matters — why the product does not smell. (Clue: what makes a molecule able to reach your nose at all?)
📖 Activity 1: Core Reaction Mechanism & Structure Analysis (25 mins)
Test both (15 min). Using the samples provided: test a carboxylic acid with blue litmus and with sodium hydrogencarbonate solution; test an amine with red litmus. Record observations. The carbonate test produces a gas — identify it and write the equation. Then explain why this pair of tests distinguishes a carboxylic acid from every other functional group you have met.
Salts and solubility (10 min). React ethanoic acid with sodium hydroxide, and ethylamine with hydrochloric acid. Draw both salts. Predict which is more soluble in water — the neutral molecule or its salt — and connect your answer back to the fish.
📝 Activity 2: Level 2 Chemistry Portfolio Task & Merit/Excellence Scaffolding (20 mins)
Organic Portfolio — Section 5. Submit: (1) your test results table with equations; (2) both salt-formation equations drawn structurally; (3) a paragraph explaining the lemon-on-fish observation using volatility and acid–base chemistry together.
🏫 Kaiako Planning & Pedagogy Notes
NCEA Level 2 Alignment: Direct preparation for NCEA Level 2 Chemistry (External) (Demonstrate understanding of the properties of selected organic compounds). Emphasise linking observations and reagents to molecular structure for Merit/Excellence grades.