Eduqas A-Level Chemistry A410QS
Formulae and Equations
Basic Ideas About Atoms
Chemical Calculations
Bonding
Solid Structures
The Periodic Table
Simple Equilibria and Acid-Base Reactions
Thermochemistry
Rates of Reaction
The Wider Impact of Chemistry
Organic Compounds
Hydrocarbons
Halogenoalkanes
Alcohols and Carboxylic Acids
Instrumental Analysis
Redox and Standard Electrode Potential
Redox Reactions
Chemistry of the P-Block
Chemistry of the D-Block Transition Metals
Chemical Kinetics
Enthalpy Changes for Solids and Solutions
Entropy and Feasibility of Reactions
Equilibrium Constants
Acid-Base Equilibria
Stereoisomerism
Aromaticity
Alcohols and Phenols
Aldehydes and Ketones
Carboxylic Acids and Their Derivatives
Amines
Amino Acids, Peptides and Proteins
Organic Synthesis and Analysis
Specified Practical Work
Practical Skills and Techniques
Mathematical Skills in Chemistry
Alcohols and Phenols
Acidity of phenol
- 3 things to know
- Component 2
Overview
Anion produced when phenol loses a proton, why phenol is a far stronger acid than ethanol and acid dissociation constant and pKa of phenol.
What you need to know
Answer each one before you reveal it.
Write the equation for the reaction of phenol with sodium metal, and explain why this reaction does not identify phenol.
Write the equation for the ionisation of phenol in aqueous solution.
Questions from this subtopic
Each one with the model answer underneath.
- 1
Give the formula of phenol and describe its appearance and melting temperature.
Model answer
Phenol is C₆H₅OH, a white crystalline solid melting at 43 °C, only slightly soluble in cold water and with a sharp antiseptic smell.
- 2
Write the equation for the ionisation of phenol in aqueous solution.
Model answer
C₆H₅OH(aq) ⇌ C₆H₅O⁻(aq) + H⁺(aq).
- 3
Name the anion produced when phenol loses a proton.
Model answer
It is the phenoxide ion.
- 4
Explain why phenol is a far stronger acid than ethanol.
Model answer
In the phenoxide ion the lone pair left on the oxygen is drawn into the delocalised π system of the ring, so the negative charge is spread over the whole ion and the anion is stabilised, whereas in the ethoxide ion the charge stays concentrated on one oxygen atom. The more stable anion means the dissociation equilibrium lies much further to the right.
- 5
Explain, in terms of the O—H bond, how attaching the hydroxyl group to a benzene ring increases acidity.
Model answer
The ring draws electron density away from the oxygen towards itself, which weakens the O—H bond and so lets the proton be released more readily.
- 6
State the acid dissociation constant and pKa of phenol.
Model answer
Ka is about 1.0 × 10⁻¹⁰ mol dm⁻³, which corresponds to a pKa of about 10.0.
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