Alcohols: making, classifying and reacting
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 3 practice questions, 3 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- The breathalyser and the colour change
- Classifying alcohols
- Making alcohols
Read the transcript of the teaching part
Last time
Before we start: last time, in Halogenoalkanes, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
The breathalyser and the colour change
The first breathalysers used orange potassium dichromate crystals. If the driver had been drinking, ethanol in the breath turned the crystals green. The ethanol had been oxidised. Alcohols are among the most versatile organic compounds, and how they react depends on a single feature: how many carbons the OH carbon is attached to.
Classifying alcohols
In a primary alcohol, the carbon bearing the OH is bonded to one other carbon. In a secondary, two. In a tertiary, three. Ethanol is primary. Butan-2-ol is secondary. 2-methylbutan-2-ol, CH three C(OH)(CH three)CH two CH three, is tertiary. The class decides what oxidation can do.
Making alcohols
Hydration of an alkene: steam and a phosphoric acid catalyst. Ethene gives ethanol. Hydrolysis of a halogenoalkane: warm with aqueous sodium hydroxide. This is nucleophilic substitution. Reduction of a carbonyl compound or carboxylic acid: sodium borohydride or lithium aluminium hydride. Fermentation of glucose is a biological route to ethanol.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Dehydration to alkenes · Oxidation of alcohols.
The whole chapter: Hydroxy Compounds, Hydroxy Compounds.
Chapter 16: Hydroxy compounds
- Alcohols: making, classifying and reacting 7 min
Also for A Level Chemistry 9701
Which topics come up most in A Level Chemistry 9701 past papers, counted from every paper since 2004: Paper 2 topic frequency, Paper 4 topic frequency.