Skip to content
Cambridge IGCSE0620

The characteristic properties of acids and bases

Chemistry 0620 Chapter Notes

What this chapter covers

The characteristic properties of acids and basesOxidesPreparation of salts
ShareWhatsAppPost
The characteristic properties of acids and bases notes

Read online free. Download a watermarked copy with a free account.

Read the notes

The full The characteristic properties of acids and bases notes as text: skim, search, and jump between subtopics.

~21 min read

In this chapter

  1. 1Reactions of acids
  2. 2Bases and alkalis
  3. 3Indicators in acids and alkalis
  4. 4Hydrogen and hydroxide ions
  5. 5pH and universal indicator
  6. 6Acids and bases as proton transfer
  7. 7Strong and weak acids
  8. 8Acidic oxides: non-metal oxides
  9. 9Basic oxides: metal oxides
  10. 10Amphoteric oxides
  11. 11Aluminium oxide and zinc oxide
  12. 12Which salts dissolve
  13. 13Soluble salt from an alkali: titration
  14. 14Soluble salt from an excess of solid
  15. 15Obtaining pure crystals
  16. 16Hydrated and anhydrous
  17. 17Insoluble salts by precipitation
  18. 18Water of crystallisation

1. Reactions of acids

An acid reacts with a metal to make a salt and hydrogen. It reacts with a base to make a salt and water. It reacts with a carbonate to make a salt, carbon dioxide and water.

Sulfuric acid makes sulfates. Magnesium and sulfuric acid make magnesium sulfate. Hydrochloric acid makes chlorides. Calcium carbonate and hydrochloric acid make calcium chloride.

Mg(s) + H₂SO₄(aq) → MgSO₄(aq) + H₂(g)

CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + CO₂(g) + H₂O(l)

Examiner insight

“Common errors included: carbon dioxide, hydrogen or hydroxide being formed when calcium oxide reacts with hydrochloric acid; water being formed when magnesium reacts with hydrochloric acid; red litmus being used as an indicator.”

Worked example 11 mark

Which products are formed when magnesium carbonate reacts with dilute hydrochloric acid?

A carbon dioxide, hydrogen and magnesium chloride · B carbon dioxide and magnesium chloride only · C carbon dioxide, water and magnesium chloride · D water and magnesium chloride only

  1. 1

    A carbonate and an acid make a salt, carbon dioxide and water. No hydrogen is made.

  2. 2

    C: carbon dioxide, water and magnesium chloride. [1]

2. Bases and alkalis

Bases are oxides or hydroxides of metals. Alkalis are soluble bases.

A base reacts with an acid to make a salt and water. A base reacts with an ammonium salt to release ammonia gas.

acid + base → salt + water

CH₃COOH(aq) + NaOH(aq) → CH₃COONa(aq) + H₂O(l)

Examiner insight

“The term alkali was less well known.” “Few candidates knew that ammonia is released when sodium hydroxide reacts with an ammonium salt.”

Worked example 11 mark

Sodium hydroxide is an alkali. State the meaning of the term alkali.

  1. 1

    An alkali is a soluble base. [1]

3. Indicators in acids and alkalis

In dilute acid, thymolphthalein is colourless and methyl orange is red.

In alkali, thymolphthalein turns blue and methyl orange turns yellow. Litmus is red in acid and turns blue in alkali.

Examiner insight

“Most did not heed the important words in the stem of the question ‘acidified solution’ and suggested that the initial colour of the methyl orange was orange rather than red.” “Some candidates confused the colours and got them the other way around.”

Worked example 12 marks

State the colour change observed when excess aqueous potassium hydroxide is added to a solution of dilute hydrochloric acid with methyl orange indicator.

  1. 1

    from red [1]

  2. 2

    to yellow [1]

4. Hydrogen and hydroxide ions

Aqueous solutions of acids contain hydrogen ions, H⁺. Aqueous solutions of alkalis contain hydroxide ions, OH⁻.

In neutralisation, an acid reacts with an alkali to make water. The H⁺ ions from the acid react with the OH⁻ ions from the alkali.

H⁺(aq) + OH⁻(aq) → H₂O(l)

Examiner insight

“In (c)(ii) few candidates knew that the H+ ion is present in all acids.” “Many candidates confused the formula and also gave equations.”

Worked example 11 mark

Give the formula of the ion that is present in all aqueous alkalis.

  1. 1

    OH⁻ [1]

5. pH and universal indicator

Universal indicator paper gives a colour for each pH. A strong acid turns it red, at about pH 1. An alkali turns it blue.

The lower the pH, the higher the hydrogen ion concentration and the more acidic the solution. pH 7 is neutral. The higher the pH above 7, the more alkaline the solution.

Examiner insight

“Better answers related the range of colours to the pH, rather than just referring to a pH scale 1 to 14 and writing about colour matching.” “Many thought that the question was about the colour of the indicator in acid rather than finding the exact pH and gave answers referring to the indicator turning red.”

Worked example 11 mark

Dilute acid HA has a pH of 2 and dilute acid HX has a pH of 4. Both acids have the same concentration.

Which statement is correct?

A HA is more acidic than HX and the hydrogen ion concentration of HA is greater than that of HX. · B HA is less acidic than HX and the hydrogen ion concentration of HA is greater than that of HX. · C HA is less acidic than HX and the hydrogen ion concentration of HA is less than that of HX. · D HA is more acidic than HX and the hydrogen ion concentration of HA is less than that of HX.

  1. 1

    HA has the lower pH, so it is more acidic and has the greater hydrogen ion concentration.

  2. 2

    A [1]

6. Acids and bases as proton transfer

An acid is a proton donor. A base is a proton acceptor.

A proton is an H⁺ ion. In an equation, the species that loses H⁺ is the acid. The species that gains H⁺ is the base. A species such as HSO₄⁻ can do both.

H₂SO₄ ⇌ H⁺ + HSO₄⁻

HSO₄⁻ ⇌ H⁺ + SO₄²⁻

Examiner insight

“Candidates should be aware that an acid is a proton donor. No other term adequately applies to all acids.” “In option C, candidates identified H2SO4 as a proton donor but did not use the equations to identify which species were gaining or losing protons, H+.”

Worked example 11 mark

Sulfuric acid dissociates in water in two stages.

H₂SO₄ ⇌ H⁺ + HSO₄⁻ and HSO₄⁻ ⇌ H⁺ + SO₄²⁻

Which statements about these equations are correct?

1 HSO₄⁻ can donate and accept protons. · 2 H₂SO₄ is a proton donor. · 3 SO₄²⁻ is the only base.

A 1 and 2 · B 1 only · C 2 and 3 · D 3 only

  1. 1

    H₂SO₄ loses H⁺, so it is a proton donor. Statement 2 is correct.

  2. 2

    HSO₄⁻ loses H⁺ in the second equation and gains it in the reverse of the first. Statement 1 is correct.

  3. 3

    HSO₄⁻ is also a base, so statement 3 is wrong.

  4. 4

    A: 1 and 2. [1]

7. Strong and weak acids

A strong acid is completely dissociated in aqueous solution. A weak acid is partially dissociated in aqueous solution.

Hydrochloric acid is a strong acid. Ethanoic acid is a weak acid, so its equation uses the equilibrium arrow.

Weak does not mean dilute. Strength is about dissociation. Concentration is about how much acid is dissolved.

HCl(aq) → H⁺(aq) + Cl⁻(aq)

CH₃COOH(aq) ⇌ H⁺(aq) + CH₃COO⁻(aq)

Examiner insight

“There is a considerable amount of confusion concerning the terms weak and dilute.” “Fewer candidates knew that as CH3COOH is a weak acid, it only partially dissociates so an equilibrium arrow should be used, as described in section 7.1.12 of the syllabus.”

Worked example 11 mark

A known mass of magnesium is added to excess dilute hydrochloric acid. The total volume of hydrogen produced is 70 cm³.

The experiment is repeated using dilute ethanoic acid in place of dilute hydrochloric acid.

All other conditions are the same.

Which row gives the relative rate of the reaction and the total volume of hydrogen produced in the second experiment?

relative rate of reactiontotal volume of hydrogen / cm³
Afaster35
Bfaster70
Cslower35
Dslower70
  1. 1

    Ethanoic acid is a weak acid. It is only partially dissociated, so it has a lower concentration of H⁺ ions and the reaction is slower.

  2. 2

    The same mass of magnesium is used with excess acid, so the same volume of hydrogen is made: 70 cm³.

  3. 3

    D: slower, 70 cm³. [1]

Recap

  • Acid + metal makes a salt and hydrogen. Acid + base makes a salt and water. Acid + carbonate makes a salt, carbon dioxide and water.
  • Bases are oxides or hydroxides of metals. Alkalis are soluble bases. A base releases ammonia from an ammonium salt.
  • Thymolphthalein: colourless in acid, blue in alkali. Methyl orange: red in acid, yellow in alkali. Litmus: red in acid, blue in alkali.
  • Acids contain H⁺ ions. Alkalis contain OH⁻ ions. Neutralisation: H⁺(aq) + OH⁻(aq) → H₂O(l).
  • Lower pH means higher hydrogen ion concentration and a more acidic solution. pH 7 is neutral.
  • Extended: an acid is a proton donor and a base is a proton acceptor.
  • Extended: a strong acid is completely dissociated, a weak acid is partially dissociated. Weak does not mean dilute.

8. Acidic oxides: non-metal oxides

An acidic oxide is the oxide of a non-metal. Sulfur dioxide, SO₂, and carbon dioxide, CO₂, are acidic oxides.

To explain the class, name the element and say it is a non-metal. The oxygen does not decide it. Carbon dioxide dissolved in water gives a solution with a pH below 7.

Examiner insight

“The best answers referred to nitrogen dioxide being an acidic oxide because the nitrogen is a non-metal and non-metal oxides are acidic.” “Many candidates, who recognised that nitrogen dioxide is an acidic oxide, gave vague explanations unrelated to its non-metallic nature such as ‘it has an acidic substance present in it’ or ‘it has an acidic pH’.”

Worked example 12 marks

Copper(II) oxide is basic. Classify the oxides in Table 4.2 as acidic or basic.

oxideacidic or basic
calcium oxide
carbon dioxide
manganese(IV) oxide
sulfur dioxide
  1. 1

    calcium oxide: basic; manganese(IV) oxide: basic (metal oxides) [1]

  2. 2

    carbon dioxide: acidic; sulfur dioxide: acidic (non-metal oxides) [1]

  3. 3

    The mark scheme gives 2 marks for all four correct and 1 mark for two or three correct.

9. Basic oxides: metal oxides

A basic oxide is the oxide of a metal. Copper(II) oxide, CuO, and calcium oxide, CaO, are basic oxides.

To explain the class, write that the element is a metal and that metal oxides are basic. Sodium oxide forms a basic solution in water. Copper(II) oxide reacts with dilute hydrochloric acid to make copper(II) chloride.

Examiner insight

“The best answers referred to sodium oxide being a basic oxide because sodium is a metal and metal oxides are basic.” “The commonest incorrect answers were ‘metal oxide’ or ‘Group II oxide’.”

Worked example 11 mark

Which oxide forms a basic solution in water?

A carbon dioxide · B nitrogen dioxide · C sodium oxide · D sulfur dioxide

  1. 1

    C: sodium oxide, the only metal oxide in the list. The other three are non-metal oxides. [1]

10. Amphoteric oxides

An amphoteric oxide is an oxide that reacts with acids and with bases to produce a salt and water.

It shows both acidic and basic behaviour. It is not the same as a neutral oxide.

Examiner insight

“Some candidates suggested that amphoteric meant a substance that reacted with neither acids or bases.” “Some candidates confused the terms neutral and amphoteric.”

Worked example 11 mark

Tin(II) oxide, SnO, is amphoteric.

Which reactions show that tin(II) oxide is amphoteric?

1 4SnO → 2SnO₂ + 2Sn 2 SnO + 2HCl → SnCl₂ + H₂O 3 2SnO + O₂ → 2SnO₂ 4 SnO + 2NaOH → Na₂SnO₂ + H₂O

A 1 and 2 · B 1 and 3 · C 2 and 3 · D 2 and 4

  1. 1

    Reaction 2 is with an acid and reaction 4 is with a base. Each gives a salt and water. Answer D. [1]

11. Aluminium oxide and zinc oxide

Al₂O₃ and ZnO are the amphoteric oxides to know. With an acid each makes a salt and water: aluminium oxide with dilute hydrochloric acid makes aluminium chloride.

With aqueous sodium hydroxide, aluminium oxide forms sodium aluminate, NaAlO₂, and zinc oxide forms sodium zincate, Na₂ZnO₂, which contains ZnO₂²⁻ ions. In the acid and in the alkali, solid zinc oxide dissolves.

Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O

Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O

ZnO + H₂SO₄ → ZnSO₄ + H₂O

Examiner insight

“Many who did try and give observations incorrectly stated there would be fizzing.”

Worked example 12 marks

Complete the equation for the reaction of aluminium oxide with aqueous sodium hydroxide by inserting the missing formula and balancing the equation.

Al₂O₃ + NaOH → NaAlO₂ +

  1. 1

    missing product is water, H₂O [1]

  2. 2

    balanced: Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O [1]

Recap

  • Acidic oxides are non-metal oxides, such as SO₂ and CO₂.
  • Basic oxides are metal oxides, such as CuO and CaO.
  • Explain the class by naming the element: it is a metal, or it is a non-metal.
  • Extended: an amphoteric oxide reacts with acids and with bases to produce a salt and water.
  • Extended: Al₂O₃ and ZnO are amphoteric oxides.

12. Which salts dissolve

Use the solubility rules to decide how a salt can be made. Sodium, potassium and ammonium salts are soluble. Nitrates are soluble.

Chlorides are soluble, except lead and silver. Sulfates are soluble, except barium, calcium and lead.

Carbonates are insoluble, except sodium, potassium and ammonium. Hydroxides are insoluble, except sodium, potassium, ammonium and calcium (partially).

Examiner insight

“Lack of knowledge of the rules of solubility made this question challenging for many candidates, and very few could name silver chloride as an insoluble chloride.” “Candidates did not recall that insoluble salts are prepared by precipitation using two soluble salts.”

Worked example 11 mark

Which two compounds react together to form the insoluble salt lead(II) chloride?

A 1 and 3 · B 1 and 4 · C 2 and 3 · D 2 and 4

compoundsolubility in water
1lead(II) nitrateyes
2lead(II) sulfateno
3silver chlorideno
4sodium chlorideyes
  1. 1

    B: 1 and 4. Both are soluble, and together they give PbCl₂. [1]

13. Soluble salt from an alkali: titration

A soluble salt can be made by reacting an acid with an alkali by titration. The acid is added to a known volume of the alkali, with an indicator, until a neutral solution is formed.

Methyl orange and thymolphthalein are suitable indicators. Universal indicator is not suitable, as it does not have a sharp single colour change at the end-point.

HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)

H⁺ + OH⁻ → H₂O

Examiner insight

“Some candidates named universal indicator.” “Some candidates thought the method was neutralisation.”

Worked example 13 marks

Dilute hydrochloric acid is added to a known volume of aqueous sodium hydroxide in the presence of an indicator until a neutral solution is formed.

(i) Write the ionic equation which represents the neutralisation reaction that takes place.

(ii) Name a suitable indicator to use.

(iii) Name the experimental technique used.

  1. 1

    H⁺ + OH⁻ → H₂O [1]

  2. 2

    methyl orange / thymolphthalein [1]

  3. 3

    titration [1]

14. Soluble salt from an excess of solid

To use an excess of metal, insoluble base or insoluble carbonate, add the solid in excess to the acid. Add it until no more dissolves, so that all the acid has reacted.

Then filter off the unreacted solid. The filtrate is the salt solution. A titration is not used, because the solid is insoluble.

CuO(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l)

ZnCO₃(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂O(l) + CO₂(g)

Examiner insight

“It was important to ensure that the copper(II) carbonate was in excess, by adding it to the nitric acid until it stopped dissolving and no more bubbles of gas were seen.” “Since copper(II) carbonate is insoluble in water, it was inappropriate to carry out a titration which many candidates did.”

Worked example 12 marks

A student makes aqueous copper(II) sulfate by reacting copper(II) carbonate with dilute sulfuric acid.

step 2 Add copper(II) carbonate to the dilute sulfuric acid in the beaker until the copper(II) carbonate is in excess.

(i) In step 2, the student observes effervescence as the copper(II) carbonate reacts with the dilute sulfuric acid. Describe one other observation that is made in step 2 before the copper(II) carbonate is in excess.

(ii) Explain why the copper(II) carbonate must be added in excess.

  1. 1

    blue solution forms / solid disappears [1]

  2. 2

    so all of the acid reacts / no acid left [1]

15. Obtaining pure crystals

After filtering, heat the filtrate to the point of crystallisation, when it is saturated. Do not heat to dryness.

Leave the hot solution to cool. Filter off the crystals and dry them between filter papers.

Examiner insight

“Ideally, this would have been evaporation until the point of crystallisation, followed by cooling, filtration, rinsing and drying.” “Evaporation to dryness would not give pure crystals.”

Worked example 16 marks

Hydrated chromium(III) nitrate is a salt which is soluble in water. Hydrated chromium(III) nitrate is made by reacting the insoluble base chromium(III) oxide with dilute nitric acid. Chromium(III) oxide reacts very slowly with dilute nitric acid at room temperature.

Describe how to make pure, dry crystals of hydrated chromium(III) nitrate. You are provided with chromium(III) oxide, dilute nitric acid and common laboratory apparatus.

  1. 1

    add chromium(III) oxide to dilute nitric acid in a named container, e.g. a beaker [1]

  2. 2

    chromium(III) oxide is in excess [1]

  3. 3

    the mixture is stirred [1]

  4. 4

    the mixture is heated / warmed to speed up the reaction [1]

  5. 5

    filter the reaction mixture [1]

  6. 6

    heat / warm the solution to remove water [1]

  7. 7

    also credited: dry the crystals, or cool and filter out the crystals (the six marks are the best six of seven points)

16. Hydrated and anhydrous

A hydrated substance is a substance that is chemically combined with water. An anhydrous substance is a substance containing no water.

Crystals of hydrated copper(II) sulfate are blue. Heating aqueous copper(II) sulfate until all the water has evaporated leaves a white solid, anhydrous copper(II) sulfate.

Examiner insight

“Many candidates wrote vague statements when defining the term ‘hydrated’.” “The commonest errors were to suggest ‘water is present’, dissolved in water’, ‘liquid’ or absorbs water’.”

Worked example 12 marks

Define the terms hydrated and anhydrous.

  1. 1

    hydrated: a substance that is chemically combined with water [1]

  2. 2

    anhydrous: a substance containing no water [1]

17. Insoluble salts by precipitation

An insoluble salt is made by precipitation. Mix aqueous solutions of two soluble salts, one with each ion needed.

The solid forms in the mixture. Filter it off, wash the residue with water, then dry it between filter papers or in a warm place.

The ionic equation has the two ions as reactants and the solid as the one product. The state symbols are (aq) for each ion and(s) for the product.

Pb²⁺(aq) + SO₄²⁻(aq) → PbSO₄(s)

Examiner insight

“Some candidates did not add water to form solutions at the start of the process, and many candidates omitted the important step of washing the precipitate after filtration.” “Candidates should be advised to identify the solid product and ‘split’ this up into its constituent ions.”

Worked example 18 marks

Lead(II) sulfate, PbSO₄, is an insoluble salt which forms when an aqueous lead(II) salt reacts with an aqueous sulfate salt.

(i) Name a lead(II) salt and a sulfate salt that will form lead(II) sulfate.

(ii) Name this technique of insoluble salt preparation.

(iii) Describe how pure lead(II) sulfate can be obtained from the reaction mixture.

(iv) Write the ionic equation for this reaction. Include state symbols.

  1. 1

    lead(II) salt, e.g. lead(II) nitrate [1]

  2. 2

    sulfate salt, e.g. sodium sulfate [1]

  3. 3

    precipitation [1]

  4. 4

    filter [1]

  5. 5

    wash the residue using water [1]

  6. 6

    dry the residue between filter papers / in a warm place [1]

  7. 7

    Pb²⁺ + SO₄²⁻ → PbSO₄ [1]

  8. 8

    state symbols: Pb²⁺(aq) + SO₄²⁻(aq) → PbSO₄(s) [1]

18. Water of crystallisation

Water of crystallisation is the water molecules present in hydrated crystals. Hydrated copper(II) sulfate crystals are CuSO₄.5H₂O and hydrated cobalt(II) chloride crystals are CoCl₂.6H₂O.

Heating to dryness drives this water off and leaves the anhydrous solid. To keep the water, heat only to the point of crystallisation and then leave to cool.

CuSO₄.5H₂O(s) →(heat) CuSO₄(s) + 5H₂O(g)

Examiner insight

“Some candidates heated the chromium(III) nitrate to dryness and so obtained anhydrous chromium(III) nitrate which they then tried to rehydrate.”

Worked example 13 marks

Crystals of hydrated copper(II) sulfate, CuSO₄.5H₂O, are blue. A student heats aqueous copper(II) sulfate until all the water has evaporated. The student obtains a white solid instead of blue hydrated copper(II) sulfate.

(i) Name the white solid the student obtains.

(ii) Describe what the student should do to get crystals of hydrated copper(II) sulfate from the aqueous copper(II) sulfate.

  1. 1

    anhydrous copper(II) sulfate [1]

  2. 2

    heat until half evaporated / until saturated / to the point of crystallisation [1]

  3. 3

    leave the heated solution to cool [1]

Recap

  • Soluble: sodium, potassium and ammonium salts, and all nitrates.
  • Chlorides are soluble except lead and silver. Sulfates are soluble except barium, calcium and lead.
  • Carbonates are insoluble except sodium, potassium and ammonium.
  • Alkali and acid: titration with an indicator. Metal, base or carbonate: add the solid in excess, then filter.
  • Pure crystals: evaporate to the point of crystallisation, cool, filter, dry. Never heat to dryness.
  • Hydrated = chemically combined with water. Anhydrous = containing no water.
  • Extended: insoluble salts by precipitation. Mix two soluble salts, filter, wash, dry.
  • Extended: water of crystallisation is the water in hydrated crystals, as in CuSO₄.5H₂O and CoCl₂.6H₂O.

End-of-chapter exercise

Test yourself on the whole chapter. Work through these before moving on.

  1. Copper(II) carbonate reacts with dilute sulfuric acid. Name the three products.3 marks
  2. State the colour of each indicator in dilute hydrochloric acid. (a) thymolphthalein (b) methyl orange2 marks
  3. Copper(II) oxide and sodium hydroxide are both bases. Only sodium hydroxide is an alkali. Explain why.2 marks
  4. Ammonium chloride is warmed with aqueous sodium hydroxide. Name the gas released and state what happens to damp red litmus paper held in the gas.2 marks
  5. (a) Give the formula of the ion present in all aqueous solutions of acids. (b) Give the formula of the ion present in all aqueous solutions of alkalis. (c) Write the ionic equation, with state symbols, for the neutralisation of an acid by an alkali.3 marks
  6. Solution P has a pH of 3. Solution Q has a pH of 6. Solution R has a pH of 12. (a) State which of P and Q is more acidic. (b) State which of P and Q has the higher hydrogen ion concentration. (c) State whether R is acidic, neutral or alkaline.3 marks
  7. Calcium oxide reacts with dilute hydrochloric acid. Write the balanced symbol equation, with state symbols.3 marks
  8. Hydrazine, N₂H₄, acts as a base when it reacts with an acid. (a) State what is meant by a base. (b) Give the formula of the ion formed when one molecule of hydrazine accepts one proton.2 marks
  9. A student tests two acid solutions with universal indicator paper. Hydrochloric acid of concentration 0.0001 mol / dm³ has pH 4. Ethanoic acid of concentration 0.1 mol / dm³ has pH 3. The student concludes: ‘Ethanoic acid has the lower pH, so it is the stronger acid.’ (a) State which solution has the higher hydrogen ion concentration. Use the pH values to give a reason. (b) Explain why the student’s conclusion is wrong. Use ideas about dissociation and the two concentrations.5 marks
  10. Methanoic acid, HCOOH, is a weak acid. It dissociates in the same way as ethanoic acid and forms the methanoate ion, HCOO⁻. (a) Write the symbol equation, with state symbols, for methanoic acid dissociating in aqueous solution. (b) Methanoate ions react with water: HCOO⁻ + H₂O ⇌ HCOOH + OH⁻ Identify the acid in the forward reaction. Give a reason in terms of protons. (c) The same mass of magnesium is added to excess dilute hydrochloric acid and to excess dilute methanoic acid of the same concentration. Compare the rate of reaction and the total volume of hydrogen produced. Explain each answer.7 marks
  11. State whether sulfur dioxide is an acidic oxide or a basic oxide.1 mark
  12. Classify copper(II) oxide, CuO, and carbon dioxide, CO₂, as acidic or basic.2 marks
  13. Calcium is in Group II of the Periodic Table. State the type of oxide that calcium oxide, CaO, is. Explain your answer.2 marks
  14. Nitrogen dioxide is an acidic oxide. Explain why.2 marks
  15. Carbon dioxide dissolves in water. State whether the pH of the solution is above 7, equal to 7 or below 7. Give the class of oxide that explains this.2 marks
  16. State what is meant by an amphoteric oxide.1 mark
  17. Four oxides are sodium oxide, aluminium oxide, sulfur dioxide and zinc oxide. Name the two that are amphoteric.1 mark
  18. Solid zinc oxide is added to dilute hydrochloric acid. Separately, solid zinc oxide is added to aqueous sodium hydroxide. State what you see in each case.2 marks
  19. Aluminium oxide reacts with aqueous potassium hydroxide. The products are water and potassium aluminate, which contains K⁺ and AlO₂⁻ ions. Zinc oxide reacts with aqueous potassium hydroxide in the same way. The products are water and potassium zincate, which contains K⁺ and ZnO₂²⁻ ions. (a) Write the formula of each salt. (b) Write the balanced equation for each reaction. (c) A student says these two reactions prove that both oxides are amphoteric. Explain what else the student must find out.5 marks
  20. A student adds four solid oxides, P, Q, R and S, to dilute hydrochloric acid and, separately, to aqueous sodium hydroxide. The table gives the results. (a) Classify each of P, Q and R as acidic, basic or amphoteric. (b) One of P, Q and R is the oxide of a non-metal. Identify it and give a reason. (c) The student says that S is amphoteric. Explain why the student is wrong. (d) One of the four oxides is zinc oxide. Identify it and write the balanced equation for its reaction with dilute hydrochloric acid. | oxide | with dilute hydrochloric acid | with aqueous sodium hydroxide | | --- | --- | --- | | P | dissolves to form a salt and water | no reaction | | Q | no reaction | dissolves to form a salt and water | | R | dissolves to form a salt and water | dissolves to form a salt and water | | S | no reaction | no reaction |7 marks
  21. Define a hydrated substance.1 mark
  22. Which one of these salts is insoluble in water: sodium carbonate, silver nitrate, lead(II) chloride or calcium chloride?1 mark
  23. A student adds zinc oxide to warm dilute sulfuric acid until no more dissolves. (a) Explain why the zinc oxide is added in excess. (b) State how the excess is removed.2 marks
  24. Potassium chloride is made from dilute hydrochloric acid and aqueous potassium hydroxide. (a) Name the technique. (b) Name a suitable indicator. (c) Explain why universal indicator is not suitable.3 marks
  25. Copper(II) carbonate is added to dilute nitric acid until it is in excess. State two observations that show the copper(II) carbonate is in excess.2 marks
  26. Copper(II) sulfate crystals are made from copper(II) oxide and warm dilute sulfuric acid. These steps are in the wrong order. A leave the hot solution to cool B filter the mixture C heat the filtrate to the point of crystallisation D add copper(II) oxide in excess E dry the crystals between filter papers F filter off the crystals Give the correct order.3 marks
  27. A student wants to make copper(II) sulfate by mixing aqueous copper(II) nitrate with aqueous sodium sulfate. Explain why this does not work.2 marks
  28. Name two aqueous compounds that react to form a precipitate of barium sulfate.2 marks
  29. Hydrated cobalt(II) chloride, CoCl₂.6H₂O, is a soluble salt. A student tries to make crystals of it from solid cobalt(II) carbonate, CoCO₃, and dilute hydrochloric acid. step 1 Add a little cobalt(II) carbonate to a large excess of dilute hydrochloric acid. step 2 Heat the solution until all the water has evaporated. (a) Write the equation for the reaction in step 1. Include state symbols. (b) Explain why step 1 does not give a pure solution of cobalt(II) chloride. State what the student should do instead. (c) Explain why step 2 does not give hydrated crystals. State what the student should do instead.6 marks
  30. Lead(II) chloride, PbCl₂, is an insoluble salt. A student has only solid lead(II) carbonate, dilute nitric acid, aqueous sodium chloride and water. Describe how to make a pure, dry sample of lead(II) chloride. Include the ionic equation, with state symbols, for the reaction that forms lead(II) chloride.7 marks

Go deeper

Practise and revise with member-only material for this chapter.

Workbook

Exam-style practice questions with full worked solutions.

Unlock with a plan

Chapter at a Glance

A single-page summary of every key idea for fast revision.

Unlock with a plan

Free notes are just the start.

Unlock every Workbook and Chapter at a Glance, and generate your own worksheets and predicted papers.

Explore plans

Related chapters

Solids, liquids and gasesElements, compounds and mixturesFormulaeElectrolysisExothermic and endothermic reactionsPhysical and chemical changes