Lesson 8: Acids & Amines | CHE 2.5

Lesson at a Glance | He Tirohanga Whakamua

Do NowVinegar (ethanoic acid) vs fishy amine odours10 min

Acid-Base Comparison MatrixCarboxylic Acids: Weak acid behaviour, blue litmus RED &

{NaHCO}_{3}

effervescence · Amines & Neutralisation: Weak base behaviour, red litmus BLUE & salt formation30 min

Portfolio EntryWrite Section 8: Carboxylic Acid & Amine Acid-Base Guide10 min

Exit DrillWrite equation for ethanoic acid

+ N a H C O_{3}

5 min

Ngā Whāinga Ako | Learning Intentions

Students will know

That Carboxylic Acids ( $- C O O H$ ) are weak acids that donate $H^{+}$ in water, turning blue litmus red and producing ${CO}_{2}$ gas bubbles with hydrogen carbonate ( ${NaHCO}_{3}$ ).
That Amines ( $- N H_{2}$ ) are weak bases that accept $H^{+}$ in water, turning red litmus blue and possessing a distinct fishy odour.
How carboxylic acids and amines undergo neutralization reactions to form soluble organic salts.

Students will demonstrate

By writing balanced molecular equations for acid-carbonate and acid-base reactions.
By completing Section 8 of their Level 2 Organic Chemistry Mastery Portfolio.

Curriculum alignment

NZC (2007) · Science · Level 7 · Material World: “Investigate and measure the chemical and physical properties of a range of groups of substances, for example, acids and bases, oxidants and reductants, and selected organic and inorganic compounds.”

Do Now | Tīmatanga Whakaaro (10 min)

Baking Soda Fizz Prompt:

"When you pour household vinegar (ethanoic acid) onto baking soda ( ${NaHCO}_{3}$ ), it fizzes vigorously. If you pour ethanol onto baking soda, nothing happens. Why?"

Unpack: Ethanoic acid ( ${CH}_{3} COOH$ ) is an acid; it reacts with hydrogen carbonate ions ( ${HCO}_{3}^{-}$ ) to produce carbon dioxide gas ( ${CO}_{2} (g)$ bubbles), water, and sodium ethanoate salt. Ethanol ( ${CH}_{3} {CH}_{2} OH$ ) is neutral and cannot react with carbonates!

Acid-Base Comparison Matrix (30 min)

🧪 Carboxylic Acids ( $- C O O H$ )

Litmus Test: Blue litmus turns RED.
Carbonate Test: $+ {NaHCO}_{3} \to$ Vigorous ${CO}_{2} (g)$ effervescence.
Odour: Sharp, vinegary smell.
Equation: ${CH}_{3} COOH + {NaHCO}_{3} \to {CH}_{3} COONa + {CO}_{2} + H_{2} O$ .

🐟 Amines ( $- N H_{2}$ )

Litmus Test: Red litmus turns BLUE.
Carbonate Test: $+ {NaHCO}_{3} \to$ No reaction (no fizz).
Odour: Fishy, ammonia-like smell.
Equation: ${CH}_{3} {NH}_{2} + HCl \to {CH}_{3} {NH}_{3}^{+} {Cl}^{-}$ (methylammonium chloride).

📁 Organic Chemistry Portfolio — Section 8: Acid-Base Diagnostic Guide

Students open their Level 2 Chemistry Portfolio and complete Section 8:

Section 8 Requirements:

1. Litmus & Carbonate Diagnostic Table: Observations for 6 unlabelled liquids (hexane, hex-1-ene, propan-1-ol, ethanoic acid, propan-1-amine, 1-chloropropane) with red litmus, blue litmus, and ${NaHCO}_{3} (a q)$ .

2. Balanced Chemical Equations: Write full structural equations for: 1) Propanoic acid $+ N a H C O_{3}$ , and 2) Ethanamine $+ H C l$ .

3. Excellence Neutralisation Rationale: 1-paragraph explanation of the neutralisation reaction between ethanoic acid and ethanamine forming ethylammonium ethanoate salt.

Exit Verification | Ka Mutu Hoki (5 min)

Exit Check:

"My Section 8 correctly identifies NaHCO₃ effervescence as the unique diagnostic test for carboxylic acids."

Teacher Planning & NCEA Alignment

NCEA Level 2 Chemistry Alignment (4 Credits External):

Acid-Base Chemistry: Demonstrate understanding of weak acid properties of carboxylic acids and weak base properties of amines.
Qualitative Identification: Use litmus paper, ${NaHCO}_{3}$ , and odour to identify functional groups.

Vocabulary: Carboxylic acid, amine, weak acid, weak base, litmus test, effervescence, ${NaHCO}_{3}$ , neutralisation, alkylammonium salt.

Other teaching approach: Guided Viewing & Practical Chemistry →

Lesson 8: Carboxylic Acids, Amines & Acid-Base Chemistry