Organic Chemistry II

Slide 1 · Learning Outcomes

What you will be able to do

In Organic Chemistry I you studied hydrocarbons (alkanes, alkenes, alkynes). Now we add a functional group, the part of the molecule that decides how it reacts.

Name and draw alkanols (–OH) and alkanoic acids (–COOH) with up to six carbon atoms.
Describe how ethanol is made by fermentation and by hydration of ethene.
Describe the chemical reactions of alkanols and alkanoic acids.
Name esters and describe esterification.
Explain how soaps are made and how soaps and soapless detergents clean.
Describe addition and condensation polymerisation and name common polymers.
State uses and environmental effects of these compounds.

Series	Functional group	General formula	Name ending
Alkanols	–OH (hydroxyl)	C_nH_2n+1OH	-ol
Alkanoic acids	–COOH (carboxyl)	C_nH_2n+1COOH	-oic acid
Esters	–COO–	RCOOR'	-yl …-oate

Slide 2 · Alkanols

The alkanol family

Activity: homologous series explorer

Carbon atoms2

Naming: find the longest chain containing the –OH, number from the end nearest the –OH, and give its position: propan-2-ol, butan-1-ol.

Physical properties: alkanols have much higher boiling points than alkanes of similar mass because of hydrogen bonding between –OH groups. Small ones mix with water in all proportions.

Slide 3 · Preparation of ethanol

Two ways to make ethanol

1. Fermentation

C₆H₁₂O₆(aq) → 2C₂H₅OH(aq) + 2CO₂(g)

Sugar (e.g. molasses from Mumias or Muhoroni) + yeast (enzyme zymase), 25–35 °C, no air. Gives about 10–15% ethanol, concentrated by fractional distillation.

2. Hydration of ethene

C₂H₄(g) + H₂O(g) → C₂H₅OH(g)

Steam + ethene over phosphoric(V) acid catalyst, about 300 °C and 60 atm. Fast, continuous and pure, but uses crude oil (non-renewable).

Activity: set up a fermentation

Tick the conditions you would use, then start.

Add yeast Keep at about 30 °C Keep at about 80 °C Fit an air lock / exclude air Bubble air through the mixture

Slide 4 · Chemical properties of alkanols

What does ethanol react with?

Tap a reagent.

Uses of ethanol: alcoholic drinks, solvent (perfumes, medicines, methylated spirit), fuel (gasohol), antiseptic, making ethanoic acid and esters. Methanol is poisonous: drinking it causes blindness and death.

Slide 5 · Alkanoic acids

Ethanoic acid: a weak organic acid

Alkanoic acids contain the –COOH group. Ethanoic acid (vinegar is 4–8% ethanoic acid) is made by oxidising ethanol. It is a weak acid: CH₃COOH ⇌ CH₃COO⁻ + H⁺.

Activity: typical acid reactions

Tap a reagent.

Test for a –COOH group: add sodium carbonate or sodium hydrogencarbonate. Effervescence of a gas that turns lime water milky (CO₂) shows an acid. Alkanols do not do this.

Slide 6 · Esters and saponification

Esters: sweet-smelling compounds

alkanol + alkanoic acid ⇌ ester + water (conc. H₂SO₄ catalyst, warm)

Activity: name the ester

Alkanol

Alkanoic acid

Saponification: making soap

Fats and oils are esters of long-chain acids (e.g. stearic acid, C₁₇H₃₅COOH) with glycerol. Boiling them with concentrated sodium hydroxide splits them:

fat/oil + NaOH(aq) → sodium salt of fatty acid (soap) + glycerol

Salting out: adding concentrated NaCl makes the soap less soluble, so it separates and floats to the top.

Slide 7 · Soaps and soapless detergents

How detergents clean

A detergent particle has a long hydrocarbon tail that is hydrophobic (dissolves in grease) and an ionic head that is hydrophilic (dissolves in water).

	Soapy detergent	Soapless detergent
Example head	–COO⁻ Na⁺ (e.g. sodium stearate)	–SO₃⁻ Na⁺ / –OSO₃⁻ Na⁺
Made from	Fats/oils + NaOH	Petroleum products + conc. H₂SO₄, then NaOH
In hard water	Forms scum (calcium stearate), wastes soap	No scum: calcium salts are soluble
Environment	Biodegradable	Some are non-biodegradable (foam on rivers); phosphates cause eutrophication

Scum: Ca²⁺(aq) + 2C₁₇H₃₅COO⁻(aq) → (C₁₇H₃₅COO)₂Ca(s)

Slide 8 · Polymers and fibres

Joining small molecules into giants

A polymer is a giant molecule made by joining many small molecules (monomers). Addition polymers form from alkenes by opening the C=C double bond; no other product forms. Condensation polymers form with loss of a small molecule (e.g. water) at each link.

Activity: addition polymer builder

Monomer

Polymer (repeat unit)

Condensation polymers: nylon (a polyamide: ropes, clothes, fishing nets) and terylene (a polyester: clothes, sails). Natural polymers: starch, cellulose, proteins, natural rubber.

Plastics: cheap, light, strong, unreactive, insulators, easily moulded. But most are non-biodegradable: litter, blocked drains, harm to animals; burning PVC releases poisonous HCl and dioxins. Kenya banned plastic carrier bags in 2017.

Slide 9 · Practice

Worked example and quick checks

Worked example: number of monomers in a polymer

A sample of polyethene has a relative molecular mass of 42 000. How many ethene molecules joined to form it? (C = 12, H = 1)

Step 1: Repeat unit is –CH₂–CH₂–, formula C₂H₄

Step 2: Mass of repeat unit = (2 × 12) + (4 × 1) = 28

Step 3: n = 42 000 ÷ 28

Answer: 1500 ethene molecules

Your turn

1. PVC has RMM 62 500. Chloroethene is C₂H₃Cl (Cl = 35.5). n = .

2. The ester formed from methanol and ethanoic acid is methyl .

3. Ethanol is oxidised by acidified potassium dichromate(VI) to ethanoic .

4. The condensed formula of propan-1-ol is .

Slide 10 · Quiz

Check your understanding

Part A: Fill in the blanks (auto-marked, 1 mark each)

1. The functional group of alkanols is the group.

2. The enzyme in yeast that converts glucose to ethanol is .

3. The catalyst for hydration of ethene is phosphoric(V) .

4. Acidified potassium dichromate(VI) changes colour from orange to when it oxidises ethanol.

5. Ethanol + sodium gives sodium ethoxide and .

6. The reaction between an alkanol and an alkanoic acid is called .

7. Boiling fats with concentrated sodium hydroxide to make soap is called .

8. The part of a detergent particle that dissolves in grease is the hydrocarbon .

9. The polymer formed from chloroethene is called .

10. Nylon is an example of a polymer.

Part B: Short answers (smart-marked against key points)

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