2022 May/June · Paper 22 · Q10 (b(i), b(ii))3 marksPreparation of salts & solubility
2022 May/June · Paper 42 · Q3 (a(i))1 markProperties of acids & bases
No questions match this filter.
References only, not question text. Open Official paper ↗ where Cambridge publishes the paper,
or see the official Cambridge past-papers page; for other papers, ask your
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.
Q1Preparation of salts & solubility · Core · Paper 2 style · 4 marks
(b) Warm the acid and add copper(II) oxide a little at a time until some is left over (excess); filter to remove the excess oxide; heat the filtrate to evaporate some water until crystallisation point (crystals form on a cold glass rod); leave to cool and crystallise, then filter/pick out the crystals and dry them between filter papers.
Add excess CuO to (warm) acid B1; filter B1; heat filtrate to crystallisation point / evaporate some water B1; cool, filter and dry crystals (e.g. on filter paper) B1
Q4Preparation of salts & solubility · Core · Paper 2 style · 4 marks
(a)Name the salt formed in each reaction.(i) zinc and dilute hydrochloric acid(ii) potassium hydroxide and dilute nitric acid(iii) magnesium carbonate and dilute sulfuric acid[3]
(b)Name the other two products of reaction (iii).[1]
Show answer
(a) (i) zinc chloride (ii) potassium nitrate (iii) magnesium sulfate
Each B1
(b) water and carbon dioxide
Both B1
Q5Preparation of salts & solubility · Standard · Paper 4 style · 4 marks
Sodium sulfate is made by titrating aqueous sodium hydroxide with dilute sulfuric acid. A few drops of indicator are used in the first titration to find the volume of acid needed.
(a)Explain why a titration is used to make sodium sulfate, instead of adding an excess of the base and filtering.[2]
(b)After finding the volume of acid, the student repeats the titration with the same volumes but without the indicator. Explain why.[1]
(c)Write the balanced equation for the reaction.[1]
Show answer
(a) Sodium hydroxide is soluble, so excess cannot be filtered off; the exact volumes must be used so the product is not contaminated with excess alkali or acid.
NaOH (base) soluble so excess cannot be removed by filtering B1; exact neutralisation needed for a pure salt B1
(b) So that the salt is not contaminated by the indicator.
B1
(c) 2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O
B1
Q6Preparation of salts & solubility · Standard · Paper 2 style · 6 marks
A student wants to make a dry sample of barium sulfate.
(a)Suggest two aqueous solutions she could mix.[2]
(b)Write the ionic equation, with state symbols, for the reaction.[2]
(c)Describe how she should obtain a pure, dry sample of the solid after mixing.[2]
Show answer
(a) e.g. barium chloride (or barium nitrate) and sodium sulfate (or dilute sulfuric acid)
Soluble barium salt B1; soluble sulfate B1
(b) Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)
Equation B1; state symbols B1
(c) Filter; wash the residue with distilled water; dry it in a warm oven or between filter papers.
Filter B1; wash with distilled water and dry B1
Q7Preparation of salts & solubility · Standard · Paper 2 style · 5 marks
Zinc sulfate crystals, ZnSO₄·7H₂O, are made from zinc oxide: ZnO + H₂SO₄ → ZnSO₄ + H₂O. One mole of ZnSO₄ in solution gives one mole of ZnSO₄·7H₂O crystals.[Ar: H, 1; O, 16; S, 32; Zn, 65]
(a)Calculate the relative formula mass of ZnSO₄·7H₂O.[1]
(b)A student reacts 4.05 g of zinc oxide with excess acid. Calculate the maximum mass of crystals that can form.[2]
(c)She obtains 11.5 g of crystals. Calculate the percentage yield to 3 significant figures.[1]
(d)Suggest one reason why the yield is less than 100 %.[1]
Q9Preparation of salts & solubility · Challenge · Paper 2 style · 5 marks
Three salts are needed for a school display: silver chloride, ammonium nitrate and zinc sulfate.
(a)For each salt, name the method of preparation (precipitation, titration, or excess insoluble base/metal/carbonate with acid) and name suitable starting materials.[3]
(b)Explain why your method for ammonium nitrate must be titration.[1]
(c)Write an ionic equation for the formation of silver chloride.[1]
(c) The solid was not completely dry / sodium chloride (soluble impurity) was not washed out.
B1
Q12Preparation of salts & solubility · Challenge · Paper 2 style · 5 marks
(a)A student makes copper(II) sulfate solution correctly but then heats it in an evaporating basin until all the water has gone. He obtains a white powder instead of blue crystals. Explain why.[2]
(b)Describe how he should have heated the solution, and how he could tell when to stop.[2]
(c)Suggest how the student could turn his white powder back into a blue solid.[1]
Show answer
(a) Heating to dryness drove off the water of crystallisation; the white powder is anhydrous copper(II) sulfate.
Water of crystallisation removed B1; anhydrous CuSO₄ is white B1
(b) Heat gently to evaporate only part of the water; stop at the crystallisation point, when a drop on a cold glass rod forms crystals (or crystals appear at the edge); then leave to cool.
Evaporate only some of the water / heat to crystallisation point B1; test with a glass rod or see crystals form, then cool B1
(c) Add water (a few drops).
B1
Q13Strong/weak acids & pH · Core · Paper 2 style · 5 marks
Five solutions are tested with universal indicator.Solution | pHV | 1W | 4X | 7Y | 9Z | 14
(a)Which solution is neutral?[1]
(b)Which solution could be a weak alkali such as aqueous ammonia?[1]
(c)Which solution has the highest concentration of hydrogen ions?[1]
(d)State the colour of universal indicator in solution V and in solution Z.[2]
Show answer
(a) X
B1
(b) Y
B1
(c) V
B1
(d) V red; Z purple (violet)
Each B1
Q14Strong/weak acids & pH · Core · Paper 1 style · 1 mark
(a)Which acid is a weak acid?[1]
Show answer
(a) A ethanoic acid
Ethanoic acid is only partly ionised in water, so it is a weak acid. The other three are strong acids that are fully ionised.
Q15Strong/weak acids & pH · Standard · Paper 2 style · 5 marks
A student compares 1.0 mol/dm³ hydrochloric acid with 1.0 mol/dm³ ethanoic acid.
(a)Predict which acid has the lower pH.[1]
(b)Equal pieces of magnesium ribbon are added to equal volumes of each acid. Describe and explain the difference in what is seen.[3]
(c)Explain why the two acids can have the same concentration but different pH values.[1]
Show answer
(a) hydrochloric acid
B1
(b) Faster fizzing with hydrochloric acid; HCl is fully ionised but ethanoic acid is only partly ionised; so HCl has a higher concentration of H⁺ ions and more frequent collisions.
(c) Concentration is the amount of acid dissolved; pH depends on the concentration of H⁺ ions, which depends on how much the acid ionises.
B1
Q16Strong/weak acids & pH · Standard · Paper 2 style · 4 marks
(a)State what is meant by an acid and a base in terms of proton transfer.[2]
(b)Hydrogen chloride gas reacts with ammonia gas: HCl + NH₃ → NH₄Cl (which contains NH₄⁺ and Cl⁻ ions). Identify the acid and the base in this reaction. Explain your answer.[2]
Show answer
(a) An acid is a proton (H⁺) donor; a base is a proton acceptor.
Each B1
(b) HCl is the acid: it donates a proton (H⁺) to NH₃; NH₃ is the base: it accepts the proton to form NH₄⁺.
HCl acid, donates H⁺ B1; NH₃ base, accepts H⁺ B1
Q17Strong/weak acids & pH · Standard · Paper 2 style · 5 marks
(a)Write an equation to show hydrochloric acid ionising in water and an equation to show ethanoic acid ionising in water.[2]
(b)Explain the difference between the arrows in your two equations.[1]
(c)Explain the difference between a dilute solution of a strong acid and a concentrated solution of a weak acid.[2]
Show answer
(a)HCl → H⁺ + Cl⁻CH₃COOH ⇌ CH₃COO⁻ + H⁺
Each B1 (⇌ needed for ethanoic acid)
(b) The single arrow shows HCl is completely ionised (strong); the reversible arrow shows ethanoic acid is only partly ionised (weak).
B1
(c) Dilute/concentrated refers to how much acid is dissolved per dm³; strong/weak refers to how fully the acid ionises.
Concentration = amount per volume B1; strength = degree of ionisation B1
Q18Strong/weak acids & pH · Challenge · Paper 2 style · 6 marks
Excess magnesium ribbon is added to 50.0 cm³ of 0.500 mol/dm³ hydrochloric acid. In a second flask, excess magnesium is added to 50.0 cm³ of 0.500 mol/dm³ ethanoic acid. Both acids are monobasic.Mg + 2HCl → MgCl₂ + H₂[One mole of gas occupies 24 dm³ at r.t.p.]
(a)Calculate the volume of hydrogen, at r.t.p., produced in the first flask. Give your answer in cm³.[3]
(b)Predict the final volume of hydrogen from the ethanoic acid, and how the time taken compares. Explain.[3]
(b) Also 300 cm³, but it takes longer; the same number of moles of acid is present, and as H⁺ ions react the ethanoic acid keeps ionising until all of it has reacted; but the H⁺ concentration at any time is lower, so the reaction is slower.
Same volume, 300 cm³ B1; takes longer B1; same moles of acid / all eventually ionises, but lower H⁺ concentration so slower B1
Q19Strong/weak acids & pH · Challenge · Paper 4 style · 6 marks
A student adds 0.10 mol/dm³ sodium hydroxide from a burette to 20.0 cm³ of dilute hydrochloric acid and measures the pH with a pH meter.Volume of NaOH / cm³ | 0 | 5.0 | 10.0 | 15.0 | 19.0 | 20.0 | 21.0 | 25.0pH | 1.0 | 1.2 | 1.5 | 1.8 | 2.6 | 7.0 | 11.4 | 12.0
(a)State the volume of sodium hydroxide needed to neutralise the acid.[1]
(b)Describe how the pH changes as the alkali is added.[2]
(c)Calculate the concentration of the hydrochloric acid in mol/dm³.[2]
(d)Write the ionic equation for the neutralisation.[1]
Show answer
(a) 20.0 cm³
B1
(b) pH rises slowly at first, then rises very sharply (from about 2.6 to 11.4) close to the neutral point, then rises slowly again.
Slow rise at first B1; sudden large rise around 20 cm³ then levelling off B1
Q23Properties of acids & bases · Standard · Paper 2 style · 4 marks
(a)Solid ammonium sulfate is warmed with aqueous sodium hydroxide. A gas is given off. Name the gas and give a test for it.[2]
(b)Write the word equation for the reaction.[1]
(c)Use this reaction to explain why a farmer should not spread slaked lime (calcium hydroxide) on a field at the same time as an ammonium fertiliser.[1]
(c) The base reacts with the ammonium salt and nitrogen is lost as ammonia gas.
B1
Q24Properties of acids & bases · Challenge · Paper 2 style · 4 marks
Rain and decomposing plant matter have made the soil in a field acidic. A farmer neutralises the acidity with calcium hydroxide. Treat the acidity as equivalent to 4.9 kg of sulfuric acid.Ca(OH)₂ + H₂SO₄ → CaSO₄ + 2H₂O[Ar: H, 1; O, 16; S, 32; Ca, 40]
(a)Calculate the number of moles of sulfuric acid in 4.9 kg.[1]
(b)Calculate the mass of calcium hydroxide needed, in kg.[2]
(c)Suggest why the farmer uses calcium hydroxide instead of sodium hydroxide.[1]
Show answer
(a) 50 mol
4900 ÷ 98 = 50 B1
(b) 3.7 kg
50 mol Ca(OH)₂ M1; 50 × 74 = 3700 g = 3.7 kg A1
(c) Calcium hydroxide is cheaper and only slightly soluble, so it is less likely to make the soil too alkaline / it is less corrosive.
B1
Q25Properties of acids & bases · Challenge · Paper 2 style · 4 marks
An antacid tablet contains 0.29 g of magnesium hydroxide, which neutralises excess stomach acid.Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O[Ar: H, 1; O, 16; Mg, 24]
(a)Calculate the number of moles of magnesium hydroxide in one tablet.[1]
(b)Calculate the volume of 0.10 mol/dm³ hydrochloric acid that one tablet can neutralise, in cm³.[2]
(c)Magnesium hydroxide is a base but not an alkali. Explain why.[1]
All six correct B3; four or five B2; two or three B1
(b) (i) non-metals (ii) metals
Both B1
Q27Types of oxide · Core · Paper 1 style · 1 mark
(a)Which oxide reacts with both dilute hydrochloric acid and aqueous sodium hydroxide?[1]
Show answer
(a) D zinc oxide
Zinc oxide is amphoteric, so it reacts with both acids and alkalis. Copper(II) oxide is basic and reacts only with acids.
Q28Types of oxide · Standard · Paper 2 style · 5 marks
(a)Aluminium oxide is an amphoteric oxide. Explain what this means.[1]
(b)Write a balanced equation for the reaction of aluminium oxide with dilute hydrochloric acid.[2]
(c)Describe a simple experiment to show that aluminium oxide is amphoteric.[2]
Show answer
(a) It reacts with both acids and bases (alkalis) to form salts.
B1
(b) Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O
Formulae B1; balancing B1
(c) Add some aluminium oxide powder to warm dilute hydrochloric acid and some to warm aqueous sodium hydroxide; it dissolves (reacts) in both.
Add to an acid and to an alkali B1; dissolves in both B1
Q29Types of oxide · Standard · Paper 3 style · 5 marks
A student burns small samples of magnesium, sulfur and carbon separately in jars of oxygen. Water and a few drops of universal indicator are then shaken in each jar.
(a)Predict the colour of the indicator in each jar and explain.[3]
(b)Write a balanced equation for the burning of magnesium.[1]
(c)State one safety precaution when burning sulfur.[1]
Show answer
(a) Magnesium: blue/purple — magnesium oxide is basic (forms an alkaline solution). Sulfur: red — sulfur dioxide is acidic. Carbon: yellow/orange — carbon dioxide forms a weakly acidic solution.
Each correct colour with reason B1
(b) 2Mg + O₂ → 2MgO
B1
(c) Use a fume cupboard (sulfur dioxide is toxic).
B1
Q30Types of oxide · Challenge · Paper 2 style · 5 marks
Four oxides, W, X, Y and Z, are tested.Oxide | effect of water | reacts with dilute HCl? | reacts with aqueous NaOH?W | dissolves, pH 13 | yes | noX | insoluble | yes | yesY | dissolves, pH 2 | no | yesZ | insoluble | no | no
(a)Classify each oxide as acidic, basic, amphoteric or neutral.[2]
(b)Suggest a possible identity for each of W, X, Y and Z from: aluminium oxide, carbon monoxide, sodium oxide, sulfur trioxide.[2]
(c)Write an equation for the reaction of oxide W with water.[1]
Show answer
(a) W basic; X amphoteric; Y acidic; Z neutral
All four B2; two or three B1
(b) W sodium oxide; X aluminium oxide; Y sulfur trioxide; Z carbon monoxide
All four B2; two or three B1
(c) Na₂O + H₂O → 2NaOH
B1
Similar questions
Questions that test the same subtopic in different years, grouped so you can work on one skill at a time.
References only: find each question in its paper (official link where available, otherwise through your school).
Preparation of salts & solubilityBanker36 questions · 9/9 sessions
