Hydroxy compounds (A Level)

• The oxygen lone pair is donated into the ring. That single fact makes phenol an acid and makes bromine water enough.

• 32.1.1 I can describe — describe the reaction with acyl chlorides to form esters using ethyl ethanoate
• 32.2.1 I can recall — recall the reactions (reagents and conditions) by which phenol can be produced: (a) reaction of phenylamine with HNO₂ or NaNO₂ and dilute acid below 10 °C to produce the diazonium salt; further warming of the diazonium salt with H₂O to give phenol
• 32.2.2 I can recall — recall the chemistry of phenol, as exemplified by the following reactions: (a) with bases, for example NaOH(aq) to produce sodium phenoxide (b) with Na(s) to produce sodium phenoxide and H₂(g) (c) in NaOH(aq) with diazonium salts, to give azo compounds (d) nitration of the aromatic ring with dilute HNO₃(aq) at room temperature to give a mixture of 2-nitrophenol and 4-nitrophenol (e) bromination of the aromatic ring with Br₂(aq) to form 2,4,6-tribromophenol
• 32.2.3 I can explain — explain the acidity of phenol
• 32.2.4 I can describe — describe and explain the relative acidities of water, phenol and ethanol
• 32.2.5 I can explain — explain why the reagents and conditions for the nitration and bromination of phenol are different from those for benzene
• 32.2.6 I can recall — recall that the hydroxyl group of a phenol directs to the 2-, 4- and 6-positions
• 32.2.7 I can — apply knowledge of the reactions of phenol to those of other phenolic compounds, e.g. naphthol

Units and significant figures are marked. The syllabus states that failure to quote units, the inclusion of units in quantities defined as ratios, and answers given to an inappropriate number of significant figures are all liable to be penalised. Give a calculated answer to the same number of significant figures as the least precise data, or one more; keep full precision in the working and round only at the end. A fifth of the qualification is experimental: Papers 3 and 5 test AO3 only, and their questions may be set in contexts outside the syllabus content, so the practical work in this chapter is set out as procedure, recording and evaluation rather than as theory.

• “Oxygen is electronegative, so it pulls electrons out of the ring and makes phenol reactive.” Correct The oxygen lone pair is donated into the ring. That single fact explains why phenol is an acid and why bromine water is enough. The lone pair sits in a p orbital that overlaps with the ring’s π system. It stabilises the phenoxide ion (acidity) and raises the ring’s electron density (activation). Write “donates into the ring”, never “withdraws”.
• “Ethanol and ethanoyl chloride are heated under reflux with concentrated sulfuric acid.” Correct The acyl chloride route works at room temperature with no catalyst, and the by-product is HCl, not water. Concentrated H₂SO₄ and heat belong to the carboxylic acid route of 16.1.2(f).
• “The diazonium salt is kept cold to speed the reaction up.” Correct It is kept below 10 °C so that it does not decompose to phenol and nitrogen before it is wanted. Warming is step 2, done on purpose once the salt has formed.
• “Phenol is an acid, so it fizzes with sodium carbonate.” Correct Phenol is a weak acid and gives no effervescence with Na₂CO₃(aq) or NaHCO₃(aq). It does react with NaOH(aq). That pair of results is the test that separates it from a carboxylic acid.
• “Phenol is brominated with Br₂ and a halogen carrier, giving bromophenol.” Correct Bromine water alone, at room temperature, with no catalyst, gives 2,4,6-tribromophenol. You see a white precipitate and the orange colour disappears. The activated ring polarises Br₂ itself and is substituted at all three activated positions.
• “Nitration of phenol gives 2-nitrophenol and 6-nitrophenol.” Correct Dilute HNO₃(aq) at room temperature gives a mixture of 2-nitrophenol and 4-nitrophenol. Positions 2 and 6 are equivalent, so a single substituent there always takes the lower locant, 2.
• “Ethanol and ethanoyl chloride are heated under reflux with concentrated sulfuric acid.” Repair Room temperature, no catalyst. Those conditions belong to the carboxylic acid route of 16.1.2(f).
• “The by-product of ethanol with ethanoyl chloride is water.” Repair The by-product is hydrogen chloride, given off as steamy fumes. The H comes from the alcohol’s O–H and the Cl from the acyl chloride.
• “Phenylamine reacts with sodium nitrite to give phenol.” Repair It takes two steps. First, NaNO₂ and dilute HCl below 10 °C give the diazonium salt. Then warming with water gives phenol and nitrogen.
• “The diazonium salt is kept cold to speed up the reaction.” Repair It is kept below 10 °C to stop it decomposing to phenol and N₂ before it is used.
• “Phenol reacts with sodium carbonate to give carbon dioxide.” Repair It does not, because phenol is too weak an acid. You see no effervescence, and that is what distinguishes it from a carboxylic acid.
• “Phenol is acidic because the O–H bond is very polar.” Repair The reason is the anion. The charge on the phenoxide ion is delocalised into the ring, which stabilises it.
• “Ethanol is a weaker acid than water because the ethyl group is bigger.” Repair The ethyl group donates electron density onto the oxygen. That raises the charge density on the ethoxide ion and destabilises it. Size is not the reason.
• “Phenol needs a halogen carrier for bromination, and gives bromophenol.” Repair Bromine water alone, at room temperature, is enough. The –OH lone pair activates the ring, which polarises Br₂ itself, and the product is 2,4,6-tribromophenol.
• “Phenol is more reactive than benzene because the electronegative oxygen pulls electrons.” Repair The oxygen’s lone pair is delocalised into the ring and raises its electron density. That is donation, not withdrawal.
• “The coupling reaction is done in acid.” Repair It is done in NaOH(aq), which turns phenol into the more strongly activating phenoxide ion, and below 10 °C.
• “4-Methylphenol with excess bromine water gives 2,4,6-tribromo-4-methylphenol.” Repair Position 4 is already taken by CH₃, so only 2 and 6 are substituted. The product is 2,6-dibromo-4-methylphenol.

• Read the command word before you decide how much to write. This syllabus has twenty-two of them: analyse, calculate, compare, consider, contrast, deduce, define, demonstrate, describe, determine, discuss, evaluate, examine, explain, give, identify, justify, predict, show (that), sketch, state and suggest. Comment, estimate, name and outline are not among them: where a question wants something named it says identify, which the syllabus glosses as “name/select/recognise”. State and give want a fact and nothing more. Describe wants the points or the features. Explain wants the reasons and the relationships — a describe-level answer to an explain question is incomplete however well written it is. Deduce and determine want a conclusion reached from the information given, with the reasoning visible.
• Answer with three things: the equation, “room temperature” (and nothing about acid or heat), and HCl as the by-product. If a question asks why this route is better, give two reasons: it is not reversible, so it goes to completion, and it is fast with no catalyst or heating.
• Conditions are part of the answer. For (a) write NaOH(aq). For (b) write Na(s) and name H₂(g). For (c) write both “in NaOH(aq)” and “below 10 °C”. Without the alkali or the temperature, the reagents and conditions are incomplete even when the product is right.
• “Describe and explain” wants both halves. Describe is the order. Explain is one reason for each end: the inductive effect for ethanol and delocalisation for phenol, each linked to the stability of the anion. An answer that gives only the order, or explains only phenol, is incomplete.
• “Predict” wants the product and a one-line reason. Name the product with its locants, then say which rule gave it: “the –OH activates 2, 4 and 6, and 4 is occupied.” An unfamiliar phenol in a question is a transfer item, not new chemistry.
• Interleave with the chapters that use this one. Chapter 33 adds carboxylic acids to the acidity series and gives the mechanism of the acyl chloride reaction; when you reach it, re-answer why phenol does not fizz with a carbonate. Chapter 34 makes the diazonium salt from phenylamine and treats azo dyes; re-answer why the coupling needs NaOH(aq) and a cold solution. Chapter 36 puts phenol into routes; re-answer the two steps from phenylamine to phenol, with their conditions. Recalling a topic inside a new context is worth more than another pass over this chapter on its own; at A Level, Paper 4 assumes the whole of the AS content, so nothing here is ever finished with.

• Cambridge International AS & A Level Chemistry 9701 has five components. Topic 32 is A Level content, so it is examined in Papers 4 and 5. A Level content: examined in Paper 4 (A Level structured, which also requires the AS content) and, as practical context, Paper 5. AS Level candidates take Papers 1, 2 and 3; A Level candidates take all five, either staged over two years (Papers 1–3 in year one, Papers 4 and 5 in year two) or together in one series. Examinations are available in the June and November series, and in March in India.
• Across both the AS Level and the A Level the assessment objectives are weighted AO1 40% (knowledge and understanding), AO2 40% (handling, applying and evaluating information) and AO3 20% (experimental skills and investigations). AS candidates are graded a–e; A Level candidates A*–E.
• There is no multiple-choice paper on A Level content, so topic 32 is met in Paper 4 structured questions. They ask you to give the reagents and conditions for making phenol or for one of its five reactions, word for word. They ask you to state an observation, write a balanced equation and explain why phenol is acidic or why it reacts more readily than benzene. They ask you to describe the relative acidities of water, phenol and ethanol, and to predict the products for a phenol you have not met. Topic 36 later puts these reactions into multi-step routes.
• The arithmetic is reacting masses and percentage yield: moles of phenol or phenylamine, the mole ratio from the equation (1 : 1 for most reactions, 1 : 3 for Br₂ and 2 : 1 for H₂), the theoretical mass and the yield, to the significant figures of the data. Relative atomic masses come from the Periodic Table you are given (C 12.0, H 1.0, N 14.0, O 16.0, Na 23.0, Cl 35.5, Br 79.9), and the molar gas volume is 24.0 dm³ mol⁻¹ at room conditions. The topic asks for the order of acidity with reasons, never for numbers, so no acidity constant appears anywhere in this chapter.
• This topic supplies two practical contexts. The first is a qualitative identification of an alcohol, a phenol and a carboxylic acid with sodium, NaOH(aq), a carbonate and bromine water, recording every “no change”. The second is a preparation with a percentage yield: brominating phenol, then filtering, washing, drying and weighing the white 2,4,6-tribromophenol and checking its melting point. A Paper 5 question can ask you to plan it, set out the results table, calculate the yield and its uncertainty, identify the largest error and explain a yield above 100%.
• Read the command word before you decide how much to write. This syllabus has twenty-two of them: analyse, calculate, compare, consider, contrast, deduce, define, demonstrate, describe, determine, discuss, evaluate, examine, explain, give, identify, justify, predict, show (that), sketch, state and suggest. Comment, estimate, name and outline are not among them: where a question wants something named it says identify, which the syllabus glosses as “name/select/recognise”. State and give want a fact and nothing more. Describe wants the points or the features. Explain wants the reasons and the relationships — a describe-level answer to an explain question is incomplete however well written it is. Deduce and determine want a conclusion reached from the information given, with the reasoning visible.