CCEA A-Level Chemistry 1110
Formulae, Equations and Amounts of Substance
Atomic Structure
Bonding
Intermolecular Forces and Structure
Shapes of Molecules and Ions
Redox
The Halogens
Acid-Base Titrations
Qualitative Tests
Formulae and Amounts of a Substance
Nomenclature and Isomerism in Organic Chemistry
Alkanes
Alkenes
Halogenoalkanes
Alcohols
Infrared Spectroscopy
Energetics
Kinetics
Equilibrium
Group II Elements and Their Compounds
Lattice Enthalpy, Entropy and Free Energy
Rates of Reaction
Equilibrium and Acid-Base Equilibria
Isomerism
Aldehydes and Ketones
Carboxylic Acids
Derivatives of Carboxylic Acids
Aromatic Chemistry
Spectroscopy and Chromatography
Volumetric Analysis
Transition Metals
Electrode Potentials
Amines
Amides and Polymers
Amino Acids and Proteins
Carboxylic Acids
Preparation from primary alcohols and aldehydes
- 3 things to know
- Unit A2 1
Overview
Why an excess of the oxidising agent is used, purpose of heating under reflux rather than distilling and colour change seen during the oxidation.
What you need to know
Answer each one before you reveal it.
Name the oxidising agent used to prepare a carboxylic acid from a primary alcohol.
Write the equation for the oxidation of ethanol to ethanoic acid using [O] for the oxidising agent.
Questions from this subtopic
Each one with the model answer underneath.
- 1
Name the oxidising agent used to prepare a carboxylic acid from a primary alcohol.
Model answer
Potassium dichromate(VI) acidified with dilute sulfuric acid is used.
- 2
Write the equation for the oxidation of ethanol to ethanoic acid using [O] for the oxidising agent.
Model answer
The equation is CH₃CH₂OH + 2[O] → CH₃COOH + H₂O.
- 3
Write the equation for the oxidation of ethanal to ethanoic acid using [O] for the oxidising agent.
Model answer
The equation is CH₃CHO + [O] → CH₃COOH.
- 4
Describe the conditions used to convert a primary alcohol completely to a carboxylic acid.
Model answer
The alcohol is heated under reflux with an excess of acidified potassium dichromate(VI) for about twenty minutes.
- 5
Explain why an excess of the oxidising agent is used.
Model answer
Two oxidation steps are needed, so enough oxidising agent must be present to take the alcohol past the aldehyde stage to the acid.
- 6
Explain the purpose of heating under reflux rather than distilling.
Model answer
Reflux condenses the vapour and returns it to the flask, so the volatile aldehyde is not lost and remains in contact with the oxidising agent.
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