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QLDChemistryQuick questions
Unit 4: Structure, synthesis and design
Quick questions on Reactions of alcohols and esterification (QCE Chemistry Unit 4)
14short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is classifying alcohols?Show answer
The oxidation behaviour of an alcohol depends on how many carbons are attached to the carbon bearing the -OH group (the alpha carbon).
What is oxidation of primary alcohols?Show answer
Primary alcohols oxidise in two steps under acidified oxidising conditions (typically acidified potassium dichromate, K2Cr2O7 in dilute H2SO4, or acidified KMnO4).
What is oxidation of secondary alcohols?Show answer
Secondary alcohols oxidise to ketones in a single step. No further oxidation occurs because the next step would require breaking a C-C bond.
What is oxidation of tertiary alcohols?Show answer
Tertiary alcohols are not oxidised by acidified dichromate or permanganate at the conditions used in school laboratories. Oxidation would require breaking a C-C bond, which is unfavourable.
What is the classification test in practice?Show answer
A common IA2 design or EA short response gives three alcohols and asks to identify them by oxidation. The decision tree:
What is esterification?Show answer
A carboxylic acid reacts with an alcohol, with concentrated sulfuric acid as catalyst, to produce an ester and water. The reaction is named after Fischer.
What is hydrolysis of esters (the reverse reaction)?Show answer
Heating an ester with dilute aqueous H2SO4 (or dilute aqueous NaOH) cleaves it back to the carboxylic acid and alcohol.
What is esters in flavour, fragrance and biology?Show answer
Most short-chain esters are volatile and smell of fruit (ethyl butanoate, pineapple; pentyl ethanoate, banana; octyl ethanoate, orange). The QCAA IA3 research investigation on flavour chemistry is a common context. Larger esters are waxes (beeswax: mainly C30 esters) and fats (triglyceride esters of glycerol with fatty acids).
What is common traps?Show answer
Forgetting "[O]" notation. QCAA marking guides accept [O] as shorthand for the oxidant (Cr2O7^2- + H+ / e- or MnO4- + H+ / e-). Show "[O]" on the reactant side of the arrow.
What is forgetting "[O]" notation?Show answer
QCAA marking guides accept [O] as shorthand for the oxidant (Cr2O7^2- + H+ / e- or MnO4- + H+ / e-). Show "[O]" on the reactant side of the arrow.
What is writing tertiary alcohol oxidation equations?Show answer
There is no equation; write "no reaction" explicitly.
What is naming the ester reversed?Show answer
Methyl propanoate is propanoic acid + methanol; propyl methanoate is methanoic acid + propan-1-ol. Different compounds, different smells, different boiling points.
What is using a single arrow for esterification?Show answer
Use a reversible arrow. The equilibrium nature of the reaction is examined in its own right.
What is confusing dehydration with oxidation?Show answer
Concentrated H2SO4 at high temperature dehydrates an alcohol to an alkene (E1 / E2 elimination). Dilute oxidising agents (acidified dichromate) oxidise to aldehyde / ketone. Conditions matter.