Alcohols and Carboxylic Acids — Part 1: Ethanol: visual lesson, ICSE Class 10 Chemistry (Science Paper 2)

Lesson

The alcohol we all know

Part 1 — Ethanol (ethyl alcohol), C₂H₅OH, is the best-known alcohol. It is the solvent in hand sanitisers and many medicines, a fuel blended with petrol, and a raw material for perfumes and vinegar. Alcohols contain the hydroxyl group, –OH, joined to a carbon chain.

In this lesson you will

Write the equation for preparing ethanol from bromoethane with aqueous alkali
Describe the nature, solubility, density and boiling point of ethanol
Write equations, with conditions, for the combustion of ethanol and its reactions with sodium, ethanoic acid and concentrated sulphuric acid
Explain why ethanol is denatured and why spurious alcohol is dangerous, and list uses of ethanol

Table of four everyday uses of ethanol and its role in each
Where you meet ethanol	What it does there
Hand sanitiser	Kills germs on the skin
Petrol blended with ethanol (E20)	Burns as a cleaner fuel
Cough syrups and tinctures	Dissolves the medicine
Spirit-filled thermometers	Stays liquid far below 0 °C

Concept

The structure of ethanol

Ethanol, CH₃–CH₂–OH, is an ethyl group joined to a hydroxyl group (–OH). The –OH group is the functional group of alcohols and decides their chemistry. Molecular formula C₂H₆O; molecular mass 46. It belongs to the homologous series CₙH₂ₙ₊₁OH (methanol, ethanol, propan-1-ol…).

Concept

Preparing ethanol: hydrolysis of bromoethane

An alkyl halide is hydrolysed by boiling it with an aqueous solution of sodium hydroxide or potassium hydroxide. The hydroxide ion replaces the halogen atom, so bromoethane gives ethanol. (With alcoholic KOH, bromoethane gives ethene instead — compare Chapter 14.)

\ce{C2H5Br + NaOH ->[{aqueous, boil}] C2H5OH + NaBr}

The OH group takes the place of the Br atom.

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