Lesson 7: Alcohol Reactions | CHE 2.5

Lesson at a Glance | He Tirohanga Whakamua

Do NowClassify propan-1-ol, propan-2-ol, 2-methylpropan-2-ol10 min

3 Key Alcohol ReactionsOxidation Reactions:

C r_{2} O_{7}^{2 -} / H^{+}

orange to green vs

M n O_{4}^{-} / H^{+}

purple to colorless · Lucas Reagent & Dehydration: Lucas test timing (

3^{\circ} & l t; 1

min) & conc.

H_{2} S O_{4}

dehydration30 min

Portfolio EntryWrite Section 7: Alcohol Oxidation & Reaction Pathways10 min

Exit DrillPredict oxidation product of propan-1-ol vs 2-methylpropan-2-ol5 min

Ngā Whāinga Ako | Learning Intentions

Students will know

How Primary ( $1^{\circ}$ ), Secondary ( $2^{\circ}$ ), and Tertiary ( $3^{\circ}$ ) alcohols react differently under oxidation:
• $1^{\circ}$ alcohol $+ C r_{2} O_{7}^{2 -} / H^{+} \to$ Carboxylic Acid (Orange $\to$ Green $C r^{3 +}$ ).
• $2^{\circ}$ alcohol $+ C r_{2} O_{7}^{2 -} / H^{+} \to$ Ketone (Orange $\to$ Green).
• $3^{\circ}$ alcohol $+ C r_{2} O_{7}^{2 -} / H^{+} \to$ NO REACTION (Remains Orange).
How Lucas Reagent ( $Z n C l_{2} / conc. H C l$ ) distinguishes alcohol classes by rate of haloalkane cloudiness ( $3^{\circ}$ rapid $& l t; 1$ min; $2^{\circ}$ 3–5 min; $1^{\circ}$ no reaction).
How Dehydration Elimination using conc. $H_{2} S O_{4}$ removes $H_{2} O$ from alcohols to form alkenes.

Students will demonstrate

By predicting observation changes for oxidation of propan-1-ol vs 2-methylpropan-2-ol.
By completing Section 7 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)

Dichromate Oxidation Prompt:

"When warm acidified potassium dichromate ( ${Cr}_{2} O_{7}^{2 -} / H^{+}$ ) is added to propan-1-ol, the orange solution turns bright green. When added to 2-methylpropan-2-ol, it stays orange. Why?"

Unpack: Propan-1-ol is a primary alcohol; it is oxidized to propanoic acid while reducing orange ${Cr}_{2} O_{7}^{2 -}$ to green ${Cr}^{3 +}$ . 2-methylpropan-2-ol is a tertiary alcohol; its carbon attached to $- O H$ has no hydrogen atom to lose, so it resists oxidation completely!

3 Key Alcohol Reactions (30 min)

🍊 1. Oxidation

$1^{\circ}$ Alcohol $\overset{{MnO}_{4}^{-} / H^{+}}{\to} Carboxylic Acid$ (Purple $\to$ Colorless ${Mn}^{2 +}$ ).
$1^{\circ}$ Alcohol $\overset{{Cr}_{2} O_{7}^{2 -} / H^{+}}{\to} Carboxylic Acid$ (Orange $\to$ Green ${Cr}^{3 +}$ ).

🧪 2. Substitution to Haloalkane

Alcohol $+ {PCl}_{5} / {SOCl}_{2} / conc. HCl \to Haloalkane$ .
Lucas Test: $3^{\circ}$ turns cloudy instantly; $2^{\circ}$ in 5 mins; $1^{\circ}$ no reaction.

💧 3. Dehydration Elimination

Alcohol $\overset{conc. H_{2} {SO}_{4}, heat}{\to} Alkene + H_{2} O$ .
Follows Saytzeff's Rule for unsymmetrical secondary alcohols.

📁 Organic Chemistry Portfolio — Section 7: Alcohol Reactions & Lucas Test

Students open their Level 2 Chemistry Portfolio and complete Section 7:

Section 7 Requirements:

1. Oxidation Comparison Table: Products and observations for $1^{\circ}, 2^{\circ}, 3^{\circ}$ alcohols with ${Cr}_{2} O_{7}^{2 -} / H^{+}$ and ${MnO}_{4}^{-} / H^{+}$ .

2. Lucas Test Diagnostic Flowchart: Describe observations and timing for adding Lucas reagent ( $Z n C l_{2} / conc. H C l$ ) to 3 structural isomers of $C_{4} H_{9} OH$ .

3. Excellence Dehydration Mechanism: 1-paragraph explanation of conc. $H_{2} {SO}_{4}$ dehydration of butan-2-ol identifying major (but-2-ene) and minor (but-1-ene) products.

Exit Verification | Ka Mutu Hoki (5 min)

Exit Check:

"My Section 7 correctly identifies propanoic acid as the product of propan-1-ol oxidation and explains why 3° alcohols resist oxidation."

Teacher Planning & NCEA Alignment

NCEA Level 2 Chemistry Alignment (4 Credits External):

Alcohol Reactions: Predict reagents, conditions, colour changes, and products for oxidation, substitution, and dehydration reactions.
Lucas Test: Distinguish primary, secondary, and tertiary alcohols based on reaction rates with Lucas reagent.

Vocabulary: Primary alcohol, secondary alcohol, tertiary alcohol, oxidation, dichromate ( ${Cr}_{2} O_{7}^{2 -}$ ), permanganate ( ${MnO}_{4}^{-}$ ), Lucas reagent, dehydration, conc. $H_{2} {SO}_{4}$ .

Other teaching approach: Guided Viewing & Practical Chemistry →

Lesson 7: Alcohols: Oxidation, Substitution & Dehydration