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school. “Paper 42” means Paper 4, variant 2.
Practice questions
Original questions written by HomiLabs in the style of the exam, with answers and mark schemes. They are not
Cambridge past paper questions and have not been reviewed by Cambridge. Try each one before opening the answer.
Q1Phenol: acidity & reactions · Core · Paper 4 style · 5 marks
(a)Write an equation for the reaction of phenol with aqueous sodium hydroxide.[1]
(b)Place ethanol, phenol and water in order of increasing acidity.[1]
(c)Explain why phenol is more acidic than ethanol.[3]
Show answer
(a) C₆H₅OH + NaOH → C₆H₅O⁻Na⁺ + H₂O
B1
(b) ethanol < water < phenol
B1
(c) In the phenoxide ion the negative charge on oxygen is delocalised into the benzene ring (a p-orbital lone pair overlaps with the π system), stabilising the anion; in ethoxide the ethyl group donates electrons, intensifying the charge on O; so phenol ionises more.
B1 phenoxide charge delocalised into ring; B1 ethoxide charge concentrated / alkyl group electron-donating; B1 more stable anion means equilibrium further to the right / more H⁺ released
Q2Phenol: acidity & reactions · Core · Paper 4 style · 5 marks
(a)Describe what is seen when bromine water is added to aqueous phenol at room temperature.[2]
(b)Write an equation for the reaction, naming the organic product.[2]
(c)State the conditions needed for benzene to react with bromine.[1]
Show answer
(a) Orange/brown bromine water is decolourised and a white precipitate forms.
(c) Liquid bromine (not bromine water) with a halogen carrier catalyst such as FeBr₃ / AlBr₃ / iron, at room temperature.
B1
Q3Phenol: acidity & reactions · Core · Paper 1 style · 1 mark
(a)Which reagent reacts with phenol but not with ethanol?[1]
Show answer
(a) B aqueous sodium hydroxide
Phenol is acidic enough to react with NaOH(aq) to form sodium phenoxide; ethanol is not. Both react with sodium metal. Phenol is too weak an acid to release CO₂ from carbonate. Dichromate oxidises ethanol, not phenol.
Q4Phenol: acidity & reactions · Standard · Paper 4 style · 6 marks
(a)Phenol reacts with dilute nitric acid at room temperature. Name the two main organic products.[2]
(b)Benzene needs a mixture of concentrated nitric and sulfuric acids at about 55 °C to be nitrated. Explain why phenol reacts under much milder conditions.[3]
(c)Write an equation for the reaction of phenol with sodium metal.[1]
Show answer
(a) 2-nitrophenol and 4-nitrophenol.
1 mark each
(b) A lone pair on the oxygen of the OH group is delocalised into the ring; this increases the electron density of the ring (especially at the 2, 4 and 6 positions); the ring is attacked more easily by electrophiles.
B1 O lone pair (p-orbital) overlaps / delocalised into π system; B1 higher electron density in ring; B1 more susceptible to electrophilic attack (ring activated)
(c) 2C₆H₅OH + 2Na → 2C₆H₅ONa + H₂
B1
Q5Phenol: acidity & reactions · Standard · Paper 1 style · 1 mark
(a)Which list shows the compounds in order of increasing acidity?[1]
Show answer
(a) B ethanol, water, phenol, ethanoic acid
Ethanol is the weakest acid (alkyl group donates electrons); water next; phenol is stronger because phenoxide is stabilised by delocalisation; ethanoic acid is strongest (carboxylate charge spread over two O atoms). D puts phenol below water.
Q6Phenol: acidity & reactions · Standard · Paper 4 style · 5 marks
(a)Phenol is dissolved in aqueous sodium hydroxide and cooled below 10 °C. A cold solution of benzenediazonium chloride is added. Describe what is seen and name the type of compound formed.[2]
(b)Give the structural formula of the product, showing where the coupling occurs on the phenol ring.[2]
(c)Explain why the reaction is carried out in alkaline solution.[1]
Show answer
(a) An orange/yellow precipitate (dye) forms; it is an azo compound.
B1 orange/yellow precipitate; B1 azo compound/dye
(b) HO–C₆H₄–N=N–C₆H₅ with the N=N joined at the 4-position (para) to the OH group.
B1 –N=N– link between two rings; B1 para to OH
(c) Phenol forms the phenoxide ion, which has a more electron-rich ring and couples more readily (and dissolves).
B1
Q7Phenol: acidity & reactions · Standard · Paper 4 style · 5 marks
(a)Give the reagents and conditions for converting phenylamine into benzenediazonium chloride.[2]
(b)State how benzenediazonium chloride is then converted into phenol and write the equation.[2]
(c)Explain why the first step must be kept below 10 °C.[1]
Show answer
(a) Sodium nitrite (NaNO₂) and dilute HCl (nitrous acid made in situ), below 10 °C.
B1 NaNO₂ + HCl; B1 below 10 °C
(b) Warm the solution with water (above 10 °C): C₆H₅N₂⁺Cl⁻ + H₂O → C₆H₅OH + N₂ + HCl
B1 warm in water; B1 equation
(c) The diazonium salt is unstable and decomposes (to phenol and N₂) at higher temperatures.
B1
Q8Phenol: acidity & reactions · Challenge · Paper 4 style · 6 marks
4.70 g of phenol is dissolved in water and an excess of bromine water is added. The yield of 2,4,6-tribromophenol is 85%.
(a)Calculate the mass of 2,4,6-tribromophenol, in g, obtained. Give your answer to 3 significant figures. (Mr: phenol = 94.0; 2,4,6-tribromophenol = 330.7)[3]
(b)Calculate the minimum mass of bromine, Br₂, in g, needed to react with all of the phenol. (Mr Br₂ = 159.8)[2]
(c)Suggest a simple test to show that the product contains no unreacted phenol.[1]
(c) Its melting point is sharp and matches the data-book value (or it gives a single spot on a chromatogram).
B1 any valid test
Q9Phenol: acidity & reactions · Challenge · Paper 4 style · 6 marks
X, Y and Z are isomers with formula C₇H₈O. Each contains a benzene ring.X reacts with aqueous NaOH and with bromine water at room temperature forming C₇H₅Br₃O.Y does not react with aqueous NaOH but reacts with sodium, giving hydrogen.Z does not react with aqueous NaOH or with sodium.
(a)Identify X, Y and Z, giving their structures and names.[3]
(b)Explain why X gives a tribromo product but 4-methylphenol would give only a dibromo product.[2]
(c)Write an equation for the reaction of Y with sodium.[1]
Show answer
(a) X: 3-methylphenol (CH₃C₆H₄OH, OH and CH₃ at 1,3); Y: phenylmethanol, C₆H₅CH₂OH; Z: methoxybenzene, C₆H₅OCH₃.
1 mark each
(b) Bromine substitutes at the 2, 4 and 6 positions relative to OH; in 3-methylphenol all three positions are free; in 4-methylphenol the 4-position is taken by CH₃, so only 2 and 6 can be substituted.
B1 2,4,6 directing by OH; B1 4-position blocked in 4-methylphenol
(c) 2C₆H₅CH₂OH + 2Na → 2C₆H₅CH₂ONa + H₂
B1
Q10Phenol: acidity & reactions · Challenge · Paper 4 style · 5 marks
Phenol, used in some antiseptics, has Ka = 1.3 × 10⁻¹⁰ mol/dm³ at 298 K.
(a)Calculate the pH of 0.100 mol/dm³ phenol. Give your answer to 2 decimal places.[2]
(b)Calculate the pH of 0.100 mol/dm³ ethanoic acid (Ka = 1.8 × 10⁻⁵ mol/dm³), to 2 decimal places.[1]
(c)Explain why ethanoic acid is a stronger acid than phenol.[2]
(c) In the ethanoate ion the negative charge is delocalised over two electronegative oxygen atoms; in phenoxide it is spread into the ring of carbon atoms (less electronegative), so it is less stabilised.
B1 carboxylate delocalised over two O atoms; B1 phenoxide charge partly on C atoms, less stable anion
Q11Alcohols: oxidation · Core · Paper 2 style · 5 marks
Propan-1-ol is warmed with acidified potassium dichromate(VI).
(a)State the colour change of the dichromate reagent.[1]
(b)Name the product formed when propan-1-ol is heated under reflux with excess acidified dichromate, and write an equation using [O].[2]
(c)Name the product formed if the oxidation is carried out with the alcohol in excess and the product distilled off immediately. Explain why distilling gives this product.[2]
(c) Propanal; it has a lower boiling point (no hydrogen bonding between molecules), so it distils out before it can be oxidised further.
B1 propanal; B1 removed from reaction mixture as formed / low b.p.
Q12Alcohols: oxidation · Core · Paper 1 style · 1 mark
(a)Which alcohol is NOT oxidised when heated under reflux with acidified potassium dichromate(VI)?[1]
Show answer
(a) D 2-methylpropan-2-ol
2-Methylpropan-2-ol is tertiary: the carbon carrying OH has no H atom, so it is not oxidised. Butan-2-ol is secondary (forms butanone); the others are primary.
Q13Alcohols: oxidation · Standard · Paper 2 style · 6 marks
(a)Name the four structural isomers of C₄H₉OH that are alcohols and classify each as primary, secondary or tertiary.[4]
(b)Name the organic product formed when butan-2-ol is heated with acidified potassium dichromate(VI).[1]
(c)State why the product of (b) cannot be oxidised further by this reagent.[1]
(c) Ketones are not oxidised; further oxidation would need a C–C bond to break.
B1
Q14Alcohols: oxidation · Standard · Paper 3 style · 5 marks
A student heats propan-1-ol and drips in acidified sodium dichromate(VI) from a dropping funnel. The flask is fitted with a still-head, thermometer and condenser set for distillation. The receiving flask stands in ice.Boiling points: propanal 49 °C; propan-1-ol 97 °C; propanoic acid 141 °C.
(a)The student wants to collect propanal. State the temperature range on the thermometer at the still-head at which she should collect the distillate.[1]
(b)Explain why the receiving flask is placed in ice.[1]
(c)Describe a test, with the result, to show that the distillate contains an aldehyde.[2]
(d)Suggest why the dichromate solution is added slowly from a dropping funnel to the warm alcohol.[1]
Show answer
(a) About 46–52 °C (around 49 °C).
B1 range including 49 °C and below 97 °C
(b) Propanal is volatile (low b.p.), so cooling reduces loss by evaporation.
B1
(c) Warm with Tollens' reagent: silver mirror forms (or warm with Fehling's solution: brick-red precipitate).
B1 reagent with warming; B1 correct positive result
(d) The alcohol stays in excess, so the aldehyde is not oxidised further (and the exothermic reaction is controlled).
B1
Q15Alcohols: oxidation · Standard · Paper 2 style · 5 marks
6.00 g of propan-2-ol is heated with excess acidified potassium dichromate(VI). 4.35 g of propanone is collected.
(a)Write an equation for the oxidation of propan-2-ol, using [O].[1]
(b)Calculate the percentage yield of propanone. Give your answer to 3 significant figures. (Mr: propan-2-ol = 60.0, propanone = 58.0)[3]
(c)Suggest one reason why the yield is below 100%.[1]
(c) Some propanone evaporates (volatile) / lost on transfer / incomplete reaction.
B1
Q16Alcohols: oxidation · Standard · Paper 1 style · 1 mark
(a)Each alcohol is warmed with acidified potassium dichromate(VI) and the product is distilled off immediately. Which alcohol gives a distillate that forms a silver mirror with Tollens' reagent?[1]
Show answer
(a) C propan-1-ol
Primary propan-1-ol gives propanal, an aldehyde, which reduces Tollens' reagent. A and D are secondary and give ketones (no silver mirror); B is tertiary and is not oxidised.
Q17Alcohols: oxidation · Challenge · Paper 2 style · 6 marks
Older roadside breath-testing devices used the oxidation of ethanol by acidified dichromate(VI).
(a)Write the half-equation for the oxidation of ethanol, C₂H₅OH, to ethanoic acid, CH₃COOH, in acidic solution.[1]
(b)The half-equation for dichromate is Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O. Construct the overall ionic equation.[2]
(c)Calculate the volume, in cm³, of 0.0200 mol/dm³ K₂Cr₂O₇ needed to oxidise 0.115 g of ethanol to ethanoic acid. Give your answer to 3 significant figures. (Mr ethanol = 46.0)[3]
Q18Alcohols: oxidation · Challenge · Paper 2 style · 5 marks
Alcohol A has molecular formula C₅H₁₂O.• A is oxidised by hot acidified dichromate(VI) to a ketone.• A has a chiral carbon atom.• Dehydration of A gives three different alkenes (counting stereoisomers).
(a)Identify A, explaining each piece of evidence.[4]
(b)Explain why 3-methylbutan-2-ol, which is also chiral and secondary, does not fit the evidence.[1]
Show answer
(a) A is pentan-2-ol, CH₃CH(OH)CH₂CH₂CH₃: secondary (oxidised to ketone, pentan-2-one); chiral C2 carries H, OH, CH₃ and C₃H₇; dehydration gives pent-1-ene plus cis- and trans-pent-2-ene (three alkenes).
B1 secondary alcohol from ketone; B1 chiral centre; B1 three alkenes explained (including cis/trans); B1 correct identity
(b) Its dehydration gives only two alkenes (3-methylbut-1-ene and 2-methylbut-2-ene), neither with cis/trans isomers.
B1
Q19Alcohols: substitution & dehydration · Core · Paper 2 style · 4 marks
(a)Give two different reagents that convert ethanol into chloroethane.[2]
(b)Write an equation for the reaction of ethanol with phosphorus(V) chloride.[1]
(c)State what is seen in (b) that makes this a test for an –OH group.[1]
Show answer
(a) Any two of: PCl₅ (room temperature); SOCl₂; PCl₃ with heat; HCl (with ZnCl₂ catalyst).
1 mark each
(b) C₂H₅OH + PCl₅ → C₂H₅Cl + POCl₃ + HCl
B1
(c) Steamy white fumes of HCl.
B1
Q20Alcohols: substitution & dehydration · Core · Paper 2 style · 4 marks
(a)Give reagents and conditions for the dehydration of ethanol.[1]
(b)Write an equation for the reaction.[1]
(c)Describe a test for the organic product, with the result.[2]
Show answer
(a) Pass vapour over heated aluminium oxide (about 350 °C) or heat with excess concentrated H₂SO₄/H₃PO₄ (about 170 °C).
B1
(b) C₂H₅OH → CH₂=CH₂ + H₂O
B1
(c) Add bromine water; orange decolourised.
B1 reagent; B1 result
Q21Alcohols: substitution & dehydration · Standard · Paper 1 style · 1 mark
(a)Butan-2-ol is heated with concentrated phosphoric acid. How many different alkenes, including stereoisomers, can form?[1]
Show answer
(a) C 3
But-1-ene forms, and but-2-ene, which has cis and trans isomers: three alkenes in total. B forgets the stereoisomers of but-2-ene.
Q22Alcohols: substitution & dehydration · Standard · Paper 2 style · 5 marks
9.20 g of ethanol is heated with potassium bromide and concentrated sulfuric acid. 14.2 g of pure bromoethane is obtained.
(a)Write equations for the formation of HBr and for its reaction with ethanol.[2]
(b)Calculate the percentage yield. Give your answer to 3 significant figures. (Mr: ethanol = 46.0, bromoethane = 108.9)[2]
(c)The crude bromoethane is orange-brown. Suggest the cause of the colour.[1]
(c) Some HBr is oxidised by concentrated sulfuric acid to bromine.
B1
Q23Alcohols: substitution & dehydration · Standard · Paper 2 style · 4 marks
(a)Write an equation for the reaction of propan-1-ol with thionyl chloride, SOCl₂.[1]
(b)Suggest one advantage of SOCl₂ over PCl₅ for this conversion.[1]
(c)State the type of reaction occurring.[1]
(d)Suggest why the reaction must be carried out in a fume cupboard.[1]
Show answer
(a) CH₃CH₂CH₂OH + SOCl₂ → CH₃CH₂CH₂Cl + SO₂ + HCl
B1
(b) Both by-products (SO₂ and HCl) are gases, so the chloroalkane is easy to separate.
B1
(c) Substitution (nucleophilic substitution of OH by Cl).
B1
(d) SO₂ and HCl are toxic/corrosive gases.
B1
Q24Alcohols: substitution & dehydration · Challenge · Paper 2 style · 6 marks
W has formula C₃H₈O₂. 0.380 g of W reacts with excess PCl₅ and gives 240 cm³ of HCl gas at room temperature and pressure (1 mol of gas occupies 24.0 dm³).
(a)Show that W contains two –OH groups. (Mr of W = 76.0)[2]
(b)Calculate the volume of hydrogen, in cm³ at r.t.p., formed when the same mass of W reacts with excess sodium.[1]
(c)Give the structures of the two possible diols. Describe a chemical test that would distinguish them, giving the result for each.[3]
Show answer
(a) n(W) = 0.380 ÷ 76.0 = 0.00500 mol; n(HCl) = 0.240 ÷ 24.0 = 0.0100 mol; ratio 1 : 2, so two OH groups (each OH gives one HCl).
(c) Propane-1,2-diol CH₃CH(OH)CH₂OH and propane-1,3-diol HOCH₂CH₂CH₂OH; warm with alkaline aqueous iodine: propane-1,2-diol gives a yellow precipitate (CHI₃) because it contains CH₃CH(OH)–; propane-1,3-diol gives no precipitate.
B1 each structure; B1 test with both results
Q25Alcohols: substitution & dehydration · Challenge · Paper 3 style · 7 marks
2-Methylbutan-2-ol is heated with concentrated phosphoric acid and the products are distilled.
(a)Name the two alkenes formed from 2-methylbutan-2-ol and explain why neither shows cis/trans isomerism.[3]
(b)In a second experiment, 10.0 g of cyclohexanol (Mr 100.0) is dehydrated and 5.74 g of cyclohexene (Mr 82.0) is collected. Calculate the percentage yield to 3 significant figures.[2]
(c)The crude cyclohexene is shaken with sodium carbonate solution and then dried with anhydrous calcium chloride. State the purpose of each step.[2]
Show answer
(a) 2-methylbut-1-ene and 2-methylbut-2-ene; in each, one carbon of the C=C carries two identical groups (two H or two CH₃).
(c) Ethanol is a weaker acid than water: the ethyl group donates electrons, making the O–H bond less polar.
B1
Q27Alcohols: reactions · Core · Paper 1 style · 1 mark
(a)Which alcohol gives a yellow precipitate when warmed with alkaline aqueous iodine?[1]
Show answer
(a) C propan-2-ol
Propan-2-ol contains the CH₃CH(OH)– group, which is oxidised and gives tri-iodomethane (CHI₃), a yellow precipitate. Methanol and propan-1-ol lack this group; 2-methylpropan-2-ol has no H on the carbinol carbon.
Q28Alcohols: reactions · Standard · Paper 2 style · 5 marks
(a)Ethanol and ethanoic acid are warmed with a few drops of concentrated sulfuric acid. Write an equation for the reaction, name the organic product and state the role of the acid.[3]
(b)Give one use of the organic product.[1]
(c)Write an equation for the complete combustion of ethanol.[1]
(b) Solvent (nail-varnish remover, glues) or flavouring.
B1
(c) C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
B1
Q29Alcohols: reactions · Challenge · Paper 2 style · 5 marks
(a)Calculate the volume of hydrogen, in dm³ at r.t.p., formed when 0.92 g of ethanol reacts with excess sodium. (1 mol of gas occupies 24.0 dm³)[2]
(b)1.48 g of an unknown alcohol, ROH, gives 240 cm³ of hydrogen with excess sodium. Calculate the Mr of the alcohol and deduce its molecular formula.[2]
(c)The alcohol gives a yellow precipitate with alkaline aqueous iodine. Identify it.[1]
