React phenol with aqueous sodium hydroxide
Use phenol's weak acidity to explain formation of sodium phenoxide and water with aqueous NaOH.
A Level; Cambridge International Chemistry 9701, 2028–2030 syllabus, Topic 32. Distinguish phenol (–OH directly on an aromatic ring) from an alcohol (–OH on an aliphatic carbon). Use the specified reagents, temperatures and products; phenol reactions are limited to those listed in the syllabus. Written practice is self-checked
Before you begin
- Recognise alcohols and phenols, aromatic substitution, acids and bases, and diazonium ions from the preceding organic topics.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What salt forms when phenol reacts with aqueous NaOH?
What you will learn
- Describe phenol reacting with NaOH(aq)
- Name sodium phenoxide as the salt product
- Relate the reaction to phenol's acidic hydrogen
Phenol can donate the O–H proton to hydroxide
Phenol is a weak acid. Aqueous sodium hydroxide removes the hydrogen from its –OH group, forming sodium phenoxide and water.
C₆H₅OH + NaOH → C₆H₅ONa + H₂O. The ionic salt contains C₆H₅O⁻ and Na⁺; the aromatic ring remains attached to oxygen.
Do not confuse phenol with an ordinary alcohol
Phenol is acidic enough to react with aqueous NaOH, whereas ethanol does not react appreciably with NaOH under the same ordinary conditions. The phenoxide ion is stabilised by delocalisation, helping explain the difference.
The product is sodium phenoxide, not sodium ethoxide. Check whether –OH is directly on the aromatic ring before choosing the product name.
Pause and explain
What other product appears in the phenol/NaOH equation?
Worked example
Write the equation for phenol reacting with aqueous NaOH.
Show the worked solution
- Remove the proton from phenol's O–H group.
- The phenoxide anion pairs with Na⁺.
- The proton combines with OH⁻ to form water.
Answer C₆H₅OH + NaOH → C₆H₅ONa + H₂O.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Write the ionic equation for phenol reacting with hydroxide ions.
Give me a hint
Show phenol donating H⁺ while preserving the ring–oxygen bond.
Compare my reasoning
- C₆H₅OH loses H⁺.
- OH⁻ gains H⁺ to form H₂O.
- C₆H₅O⁻ remains as phenoxide.
C₆H₅OH + OH⁻ → C₆H₅O⁻ + H₂O.
Look for these in your work
- Acid identified
- Conjugate base correct
- Water formed
Explain why phenol reacts with NaOH but ethanol does not appreciably do so under the same ordinary conditions.
Give me a hint
Compare the stability of phenoxide and ethoxide ions.
Compare my reasoning
- Phenol forms a phenoxide ion whose negative charge is delocalised into the ring.
- Ethanol forms ethoxide with charge localised mainly on oxygen.
- Phenol is sufficiently more acidic to be deprotonated by hydroxide.
Phenol is more acidic because phenoxide is stabilised by delocalisation; ethoxide lacks the same stabilisation, so ethanol is not appreciably deprotonated by NaOH under these conditions.
Look for these in your work
- Phenol acidity stated
- Conjugate bases compared
- Reactivity difference linked
A learner writes C₆H₅OH + NaOH → C₆H₅ONa + H₂. Identify the incorrect product and correct it.
Give me a hint
This is neutralisation with hydroxide, not reaction with sodium metal.
Compare my reasoning
- NaOH supplies OH⁻.
- The proton and hydroxide form water.
- Hydrogen gas is not formed.
Replace H₂ with H₂O: C₆H₅OH + NaOH → C₆H₅ONa + H₂O.
Look for these in your work
- Reagent role identified
- By-product corrected
- Equation restored
Common mistakes
- Writing sodium ethoxide as the product
- Claiming phenol is a strong acid
- Leaving water out of the neutralisation equation
- Breaking the ring–oxygen bond instead of the O–H bond
What can you explain now?
What salt forms when phenol reacts with aqueous NaOH?
Compare with the explanation
Sodium phenoxide
Phenol loses H⁺ and forms the phenoxide anion.
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Make it stick
How does phenol's acidic O–H group lead to sodium phenoxide and water?
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