Alcohols Flashcards

Active recall practice for classification, production, oxidation, and dehydration of alcohols.

Classification & Production: read all 8 questions and answers

What is a primary alcohol?
An alcohol where the -OH group is attached to a carbon atom that is bonded to only one other carbon atom (or none, e.g. methanol).
What is a secondary alcohol?
An alcohol where the -OH group is attached to a carbon atom that is bonded to two other carbon atoms.
What is a tertiary alcohol?
An alcohol where the -OH group is attached to a carbon atom that is bonded to three other carbon atoms.
State the reagent and conditions for industrial production of ethanol from ethene.
Direct hydration with steam at 300 degrees C, 60-70 atm pressure, using a concentrated phosphoric acid (H₃PO₄) catalyst.
State the conditions required for the fermentation of glucose to produce ethanol.
Yeast, anaerobic conditions (absence of oxygen), and a warm temperature (approx 35-40 degrees C) in aqueous solution.
Write the balanced equation for the fermentation of glucose.
C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
Define biofuel.
A fuel produced from biomass (recently living biological material).
Why is ethanol produced by fermentation not strictly carbon-neutral?
Although plants absorb 6 CO₂ to make glucose, and 6 CO₂ are released overall in fermentation and combustion, energy (releasing CO₂) is required for mechanical farming, transport, distillation, and processing.

Oxidation of Alcohols: read all 7 questions and answers

What oxidizing agent is used to oxidize alcohols?
Acidified potassium dichromate(VI) (K₂Cr₂O₇ / H₂SO₄).
What is the colour change when acidified potassium dichromate(VI) is reduced?
Orange to green (due to Cr₂O₇²⁻ reduced to Cr³⁺).
What products can be formed by the oxidation of a primary alcohol?
An aldehyde (distilled off immediately) or a carboxylic acid (heated under reflux with excess oxidising agent).
What product is formed by the oxidation of a secondary alcohol?
A ketone (heated under reflux).
Why are tertiary alcohols resistant to oxidation by acidified potassium dichromate(VI)?
There is no hydrogen atom attached to the carbon atom that carries the -OH group, meaning a strong C-C bond would have to be broken.
How do you distinguish aldehydes from ketones using Fehling's solution?
Aldehydes reduce Fehling's solution, changing it from a blue solution to a red/brick-red precipitate of copper(I) oxide. Ketones show no reaction (remains blue).
How do you distinguish aldehydes from ketones using Tollens' reagent?
Aldehydes reduce Tollens' reagent ([Ag(NH₃)₂]⁺) to form a silver mirror on the inside of the tube. Ketones show no reaction.

Elimination (Dehydration): read all 4 questions and answers

What is dehydration of an alcohol?
An elimination reaction where an alcohol loses a water molecule to form an alkene.
State the reagents and conditions for the dehydration of alcohols.
Heat with concentrated sulfuric acid (H₂SO₄) or concentrated phosphoric acid (H₃PO₄) at approx 170 degrees C, or pass vapours over a hot alumina catalyst.
Why is the dehydration of alcohols an important industrial process?
It allows the production of alkenes (which can make polymers) from renewable resources (via fermentation of glucose to ethanol) without relying on crude oil.
Write the mechanism for the acid-catalysed dehydration of ethanol.
1) Protonation of the -OH group by H⁺ to form −OH₂⁺; 2) Loss of H₂O to form a carbocation; 3) Loss of H⁺ from an adjacent carbon to reform the catalyst and form the C=C double bond.