(I once brought a bottle of hand sanitiser, a bottle of vinegar, and a bottle of perfume to class. I asked, "What do these three things have in common?" Silence. Then I said, "They are all organic compounds. And every one of them belongs to a family we are about to study." That is what this chapter is about — the organic chemistry of things you use every single day. Not abstract formulas, but real substances you can smell, taste, and touch. Once you see the chemistry behind them, you will never look at a bottle of vinegar the same way again.) Look around your home. The hand sanitiser on your shelf contains ethanol — an alcohol. The vinegar in your kitchen contains ethanoic acid — a carboxylic acid. The perfume you wear contains esters — sweet-smelling compounds made from alcohols and acids. Every one of these is an organic compound, and every one of them has a story. In this chapter, we are going to tell those stories. We will learn about alcohols (alkanols), the family of compounds with the -OH group. We will learn about carboxylic acids (alkanoic acids), the family with the -COOH group. We will see how they are prepared, how they react, and how they are used. And we will discover that organic chemistry is not just in the lab — it is in your hands, your home, and your life. Let us begin.
An alkanol (commonly called an alcohol) is an organic compound that contains the hydroxyl group (–OH) attached to a carbon atom. The general formula for alkanols with one hydroxyl group is CₙH₂ₙ₊₁OH.
| Name | Molecular Formula | Structural Formula | Common Name |
|---|---|---|---|
| Methanol | CH₃OH | CH₃OH | Methyl alcohol |
| Ethanol | C₂H₅OH | CH₃CH₂OH | Ethyl alcohol |
| Propanol | C₃H₇OH | CH₃CH₂CH₂OH | Propyl alcohol |
| Butanol | C₄H₉OH | CH₃CH₂CH₂CH₂OH | Butyl alcohol |
Naming: Alkanols are named by taking the alkane name and changing the ending from -e to -ol. So methane becomes methanol, ethane becomes ethanol, and so on.
| Property | Description |
|---|---|
| Solubility in water | The first few alkanols (methanol, ethanol, propanol) are completely soluble in water. Solubility decreases as the chain gets longer. |
| Boiling point | Higher than alkanes of similar size, because of hydrogen bonding between the –OH groups. |
| State at room temp | Methanol, ethanol, propanol are liquids; longer alkanols are solids. |
| Smell | Characteristic smell; some are pleasant, some are not. |
(Why do alkanols have higher boiling points than alkanes of similar size? Because of hydrogen bonding. The –OH group allows alkanol molecules to stick to each other more strongly than alkanes can. More energy is needed to pull them apart, so the boiling point is higher. This is a classic example of how a functional group changes physical properties.)
Alkanols can be prepared by two main methods:
Fermentation is the process by which glucose is converted to ethanol and carbon dioxide by the action of yeast enzymes.
C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
Conditions: Yeast, warm temperature (about 25–35°C), absence of air (anaerobic).
Uses: Making alcoholic drinks, bioethanol fuel.
Alkenes react with steam in the presence of a catalyst (phosphoric acid, H₃PO₄) to form alkanols.
C₂H₄ + H₂O → C₂H₅OH
Conditions: High temperature (about 300°C), high pressure, phosphoric acid catalyst.
Uses: Industrial production of ethanol.
| Alkanol | Use |
|---|---|
| Methanol | Fuel, solvent, making formaldehyde (for plastics) |
| Ethanol | Alcoholic drinks, hand sanitiser, fuel (bioethanol), solvent |
| Propanol | Solvent, antiseptic |
| Glycerol | Moisturisers, food additive, making nitroglycerin |
Warning: Methanol is highly toxic. Even small amounts can cause blindness or death. Ethanol is the alcohol in drinks, but it is still a drug and can be harmful in excess.
An alkanoic acid (commonly called a carboxylic acid) is an organic compound that contains the carboxyl group (–COOH). The general formula is CₙH₂ₙ₊₁COOH.
| Name | Molecular Formula | Structural Formula | Found In |
|---|---|---|---|
| Methanoic acid | HCOOH | HCOOH | Ant stings, nettle stings |
| Ethanoic acid | CH₃COOH | CH₃COOH | Vinegar |
| Propanoic acid | C₂H₅COOH | CH₃CH₂COOH | Some dairy products |
| Butanoic acid | C₃H₇COOH | CH₃CH₂CH₂COOH | Rancid butter |
Naming: Alkanoic acids are named by taking the alkane name and changing the ending to -oic acid. Methane → methanoic acid, ethane → ethanoic acid.
Alkanoic acids show the typical reactions of acids, but they are weak acids.
An ester is formed when an alkanoic acid reacts with an alkanol in the presence of a strong acid catalyst (usually concentrated sulphuric acid). This reaction is called esterification.
General equation:
Alkanoic acid + Alkanol → Ester + Water
Example:
Ethanoic acid + ethanol → ethyl ethanoate + water
CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O
Naming esters: The name comes from the alkanol first (as an alkyl group) and the acid second (as an alkanoate). So ethanol + ethanoic acid → ethyl ethanoate.
| Alkanol | Acid | Ester | Smell |
|---|---|---|---|
| Methanol | Ethanoic acid | Methyl ethanoate | Sweet, fruity |
| Ethanol | Ethanoic acid | Ethyl ethanoate | Pear drops |
| Propanol | Ethanoic acid | Propyl ethanoate | Pears |
| Butanol | Ethanoic acid | Butyl ethanoate | Bananas |
| Pentanol | Ethanoic acid | Pentyl ethanoate | Apples |
(Esters are the reason fruit smells like fruit. The next time you smell a banana or a strawberry, remember — you are smelling esters. Chemists can make artificial fruit flavours by mixing the right alkanol with the right acid. That is organic chemistry you can literally taste.)
Soap has been made for thousands of years. The process is called saponification — the hydrolysis of fats and oils with a strong alkali.
General reaction:
Fat/oil + Sodium hydroxide → Soap + Glycerol
Soap molecules have two ends:
How soap works: The hydrophobic tails burrow into the grease, while the hydrophilic heads stick out into the water. This forms a ball-like structure called a micelle, which lifts the grease off the surface and suspends it in water so it can be rinsed away.
Detergents work in the same way, but they are synthetic. They were developed because soap forms a scum with hard water, while detergents do not. Detergents are often made from petroleum products and are designed to work in hard water.
| Feature | Soap | Detergent |
|---|---|---|
| Source | Fats and oils (natural) | Petroleum products (synthetic) |
| Behaviour in hard water | Forms scum | Does not form scum |
| Biodegradability | Readily biodegradable | Some are not (though modern ones are) |
| Cleaning power | Good in soft water | Good in both soft and hard water |
Question: Name the alkanol with the structure CH₃CH₂CH₂OH.
Solution: It has three carbon atoms and an –OH group. The alkane with three carbons is propane. Changing the ending to -ol gives propanol. So the name is propanol (or propan-1-ol if you want to specify the position of the –OH group).
Question: Name the ester formed when propanoic acid reacts with methanol.
Solution: The alkanol is methanol (methyl group), and the acid is propanoic acid (propanoate). The ester is methyl propanoate.
Question: Describe the oxidation of ethanol to ethanoic acid, stating the reagent and the colour change observed.
Solution: Ethanol is oxidised by acidified potassium dichromate(VI). The dichromate ion is reduced from orange (Cr₂O₇²⁻) to green (Cr³⁺). The ethanol is oxidised to ethanoic acid. Equation: C₂H₅OH + 2[O] → CH₃COOH + H₂O.
Question: Explain why soap forms a scum with hard water, but detergents do not.
Solution: Hard water contains dissolved calcium and magnesium ions. Soap reacts with these ions to form insoluble calcium and magnesium salts — this is the scum. Detergents are synthetic and do not form insoluble salts with calcium and magnesium ions, so they do not form scum. This is why detergents are preferred in hard water areas.
1. What is the functional group in an alkanol?
The hydroxyl group (–OH).
2. Write the general formula for an alkanol and an alkanoic acid.
Alkanol: CₙH₂ₙ₊₁OH. Alkanoic acid: CₙH₂ₙ₊₁COOH.
3. Name the ester formed from ethanol and ethanoic acid.
Ethyl ethanoate.
4. What is the difference between soap and detergent?
Soap is made from natural fats and oils and forms scum with hard water. Detergents are synthetic (from petroleum products) and do not form scum with hard water.
5. Describe the preparation of ethanol by fermentation.
Glucose is converted to ethanol and carbon dioxide by yeast enzymes in the absence of air, at warm temperatures (25–35°C). Equation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂.
6. What reagent is used to oxidise ethanol to ethanoic acid, and what colour change is observed?
Acidified potassium dichromate(VI). The colour changes from orange to green.
7. State two uses of esters.
Any two of: flavourings and fragrances, solvents, plasticisers, making polyesters.
Question 1 [10 marks]
(a) Define an alkanol and give the general formula. [2]
(b) Describe the chemical test to distinguish between ethanol and ethanoic acid. [3]
(c) Ethanol can be oxidised to ethanoic acid. State the reagent used and the colour change observed. [3]
(d) State one use of ethanol and one use of ethanoic acid. [2]
(a) An alkanol is an organic compound containing the hydroxyl group (–OH). General formula: CₙH₂ₙ₊₁OH. (2 marks: 1 for definition, 1 for formula.)
(b) Add a few drops of universal indicator to each. Ethanoic acid (a carboxylic acid) will turn the indicator red/orange (acidic). Ethanol (a neutral alcohol) will not change the colour significantly. Alternatively, add sodium carbonate — ethanoic acid will fizz (CO₂ released); ethanol will not. (3 marks: 1 for method, 2 for observation.)
(c) Acidified potassium dichromate(VI). The colour changes from orange to green. (3 marks: 1 for reagent, 1 for orange, 1 for green.)
(d) Ethanol: alcoholic drinks, hand sanitiser, fuel. Ethanoic acid: vinegar, food flavouring, making esters. (2 marks: 1 for each.)
Question 2 [10 marks]
(a) Describe how an ester is formed from an alkanol and an alkanoic acid, including the name of the reaction. [3]
(b) Name the ester formed from methanol and propanoic acid. [2]
(c) State two uses of esters. [2]
(d) Explain why esters have pleasant smells. [3]
(a) An ester is formed when an alkanoic acid reacts with an alkanol in the presence of a strong acid catalyst (usually concentrated sulphuric acid). The reaction is called esterification. Water is also produced. (3 marks: 1 for reactants, 1 for catalyst, 1 for "esterification".)
(b) Methyl propanoate. (2 marks: 1 for "methyl", 1 for "propanoate".)
(c) Any two of: flavourings and fragrances, solvents, plasticisers, making polyesters. (2 marks: 1 for each.)
(d) Esters have pleasant smells because their molecules have the right shape and functional groups to interact with the olfactory receptors in our noses. Different esters have different smells, which is why they are used to create artificial fruit flavours and perfumes. (3 marks: 1 for "interact with receptors", 1 for "different esters different smells", 1 for "used in flavours/fragrances".)
Question 3 [10 marks]
(a) Explain how soap is able to remove grease from a dirty plate. Use the terms hydrophobic, hydrophilic, and micelle in your answer. [5]
(b) Distinguish between soap and detergent. [3]
(c) State two environmental problems caused by detergents. [2]
(a) Soap molecules have two ends: a long hydrocarbon tail that is hydrophobic (water-hating) and a charged head that is hydrophilic (water-loving). When soap is added to water and a greasy plate, the hydrophobic tails burrow into the grease, while the hydrophilic heads stick out into the water. This forms a ball-like structure called a micelle, with the grease trapped in the centre. The micelles are suspended in the water and can be rinsed away, taking the grease with them. (5 marks: 1 for hydrophobic tail, 1 for hydrophilic head, 1 for micelle, 1 for grease removal, 1 for clarity.)
(b) Soap is made from natural fats and oils and forms scum with hard water. Detergents are synthetic (from petroleum products) and do not form scum with hard water. (3 marks: 1 for source, 1 for hard water behaviour, 1 for comparison.)
(c) Some detergents are not readily biodegradable and can cause foam pollution in rivers. They can also contain phosphates that cause eutrophication. (2 marks: 1 for each.)
Challenge 1: Explain why alkanols have higher boiling points than alkanes of similar molecular mass.
Alkanols have higher boiling points than alkanes of similar molecular mass because of hydrogen bonding. The –OH group in alkanols allows the molecules to form hydrogen bonds with each other — the slightly positive hydrogen of one –OH group is attracted to the slightly negative oxygen of another. These hydrogen bonds are stronger than the weak van der Waals forces between alkane molecules, so more energy is needed to separate the alkanol molecules during boiling. This is why alkanols have higher boiling points than the corresponding alkanes.
Challenge 2: A student says, "Methanol and ethanol are both alcohols, so they must be safe to drink." Is this statement accurate? Explain your reasoning.
The statement is not accurate. While both methanol and ethanol are alkanols, they have very different effects on the human body. Ethanol is the alcohol found in alcoholic drinks and is relatively safe in moderate amounts (though still a drug that can cause harm in excess). Methanol, however, is highly toxic. When methanol is ingested, it is metabolised in the body to formaldehyde and formic acid, which are extremely poisonous. Even small amounts of methanol can cause blindness, organ damage, or death. So while both are alkanols, they are not equally safe — methanol is a dangerous poison, and ethanol is the only alkanol safe for human consumption, and even then only in moderation.
Challenge 3: Explain why the reaction between an alkanol and an alkanoic acid is called "esterification" and why a strong acid catalyst is needed.
The reaction is called esterification because it produces an ester as the main product. It is a condensation reaction — water is also produced. A strong acid catalyst (usually concentrated sulphuric acid) is needed because the reaction between an alkanol and an alkanoic acid is very slow at room temperature. The acid catalyst speeds up the reaction by protonating the carboxylic acid, making it more reactive towards the alcohol. Without the catalyst, the reaction would take a very long time to reach completion. The catalyst also helps drive the equilibrium towards the product, increasing the yield of ester.
"Alkanols and alkanoic acids — the -OH and -COOH families — are the foundation of flavours, fragrances, fuels, and life itself. Now you know the chemistry behind the everyday."
