Chemical changes
50 exam-style questions with answers for 4.4 Chemical changes in AQA GCSE Chemistry (spec 8462). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below. Not official AQA material.
All 50 questions and answers
Question 1 · Spec 4.4.1.1 · Metal oxides
What is oxidation in terms of oxygen? [1 mark]
Answer:The gain of oxygen.Question 2 · Spec 4.4.1.1 · Metal oxides
What is reduction in terms of oxygen? [1 mark]
Answer:The loss of oxygen.Question 3 · Spec 4.4.1.2 · Reactivity series
Place these in order of reactivity, most reactive first: copper, potassium, zinc, magnesium. [1 mark]
Answer:Potassium, magnesium, zinc, copper.Question 4 · Spec 4.4.1.2 · Reactivity series
Why are carbon and hydrogen included in the reactivity series? [1 mark]
Answer:They are non-metals used to compare reactivity, for example carbon can reduce metals below it.Question 5 · Spec 4.4.1.2 · Reactivity series
Explain the reactivity of a metal in terms of ions. [1 mark]
Answer:More reactive metals lose electrons more easily to form positive ions.Question 6 · Spec 4.4.1.2 · Displacement
What happens when zinc is added to copper sulfate solution? [2 marks]
Answer:Zinc displaces copper, as zinc is more reactive (1); the blue solution fades and a brown/pink coating of copper forms (1).Question 7 · Spec 4.4.1.3 · Extraction
How are metals less reactive than carbon extracted? [1 mark]
Answer:By reduction with carbon.Question 8 · Spec 4.4.1.3 · Extraction
Why is gold found as the metal itself? [1 mark]
Answer:It is very unreactive.Question 9 · Spec 4.4.1.3 · Extraction
Write the word equation for extracting iron from iron oxide using carbon. [1 mark]
Answer:Iron oxide + carbon → iron + carbon dioxide.Question 10 · Spec 4.4.1.4 · Redox · Higher only
What are oxidation and reduction in terms of electrons? [2 marks]
Answer:Oxidation is the loss of electrons (1); reduction is the gain of electrons (1).Question 11 · Spec 4.4.1.4 · Ionic equations · Higher only
Write the ionic equation for zinc displacing copper ions. [1 mark]
Answer:Zn + Cu²⁺ → Zn²⁺ + Cu.Question 12 · Spec 4.4.1.4 · Redox · Higher only
In Zn + Cu²⁺ → Zn²⁺ + Cu, which species is oxidised? [1 mark]
Answer:Zinc (it loses electrons).Question 13 · Spec 4.4.2.1 · Acids and metals
Write the word equation for magnesium reacting with hydrochloric acid. [1 mark]
Answer:Magnesium + hydrochloric acid → magnesium chloride + hydrogen.Question 14 · Spec 4.4.2.1 · Acids and metals · Higher only
Explain why the reaction of a metal with acid is a redox reaction. [2 marks]
Answer:The metal atoms lose electrons and are oxidised (1); the hydrogen ions gain electrons and are reduced (1).Question 15 · Spec 4.4.2.2 · Neutralisation
Write the word equation for copper oxide reacting with sulfuric acid. [1 mark]
Answer:Copper oxide + sulfuric acid → copper sulfate + water.Question 16 · Spec 4.4.2.2 · Neutralisation
What are the products when an acid reacts with a metal carbonate? [1 mark]
Answer:A salt, water and carbon dioxide.Question 17 · Spec 4.4.2.2 · Salts
Which acid produces chlorides, sulfates and nitrates? [3 marks]
Answer:Hydrochloric acid gives chlorides (1); sulfuric acid gives sulfates (1); nitric acid gives nitrates (1).Question 18 · Spec 4.4.2.2 · Salts
Write the formula of calcium nitrate. [1 mark]
Answer:Ca(NO₃)₂.Question 19 · Spec 4.4.2.3 · Required practical 1
Describe how to make pure dry copper sulfate crystals from copper oxide. [3 marks]
Answer:Add excess copper oxide to warm sulfuric acid and stir (1); filter to remove the excess copper oxide (1); heat the solution to evaporate some water, then leave to crystallise and pat the crystals dry (1).Question 20 · Spec 4.4.2.3 · Required practical 1
Why is the metal oxide added in excess? [1 mark]
Answer:To make sure all the acid has reacted.Question 21 · Spec 4.4.2.4 · pH
What range of pH values shows a strong acid and a strong alkali? [2 marks]
Answer:Acids: pH less than 7 (strong around 0–2) (1); alkalis: pH greater than 7 (strong around 12–14) (1).Question 22 · Spec 4.4.2.4 · Acids and alkalis
What ions do acids and alkalis produce in aqueous solution? [2 marks]
Answer:Acids produce hydrogen ions, H⁺ (1); alkalis produce hydroxide ions, OH⁻ (1).Question 23 · Spec 4.4.2.4 · Neutralisation
Write the ionic equation for neutralisation. [1 mark]
Answer:H⁺(aq) + OH⁻(aq) → H₂O(l).Question 24 · Spec 4.4.2.4 · pH
How can the pH of a solution be measured? [1 mark]
Answer:Using universal indicator or a pH probe.Question 25 · Spec 4.4.2.5 · Required practical 2
Describe how to carry out a titration. [3 marks]
Answer:Measure 25.0 cm³ of alkali into a conical flask with a pipette and add indicator (1); add acid from a burette until the indicator just changes colour (1); record the volume and repeat to get concordant results (1).Question 26 · Spec 4.4.2.6 · Strong and weak acids · Higher only
What is the difference between a strong and a weak acid? [2 marks]
Answer:A strong acid is completely ionised in aqueous solution (1); a weak acid is only partially ionised (1).Question 27 · Spec 4.4.2.6 · Strong and weak acids · Higher only
Give an example of a strong acid and a weak acid. [2 marks]
Answer:Strong: hydrochloric, nitric or sulfuric acid (1); weak: ethanoic, citric or carbonic acid (1).Question 28 · Spec 4.4.2.6 · pH · Higher only
How does the H⁺ concentration change when pH decreases by 1? [1 mark]
Answer:It increases by a factor of 10.Question 29 · Spec 4.4.2.6 · Concentrated and strong · Higher only
What is the difference between a concentrated acid and a strong acid? [2 marks]
Answer:Concentration is the amount of acid in a given volume of water (1); strength is how fully the acid ionises (1).Question 30 · Spec 4.4.3.1 · Electrolysis
What is electrolysis? [2 marks]
Answer:The breakdown of an ionic compound using electricity (1); when it is melted or dissolved, so the ions can move to the electrodes (1).Question 31 · Spec 4.4.3.1 · Electrolysis
Which ions move to the cathode and which to the anode? [2 marks]
Answer:Positive ions move to the negative cathode (1); negative ions move to the positive anode (1).Question 32 · Spec 4.4.3.2 · Molten compounds
Name the products of the electrolysis of molten lead bromide. [2 marks]
Answer:Lead at the cathode (1); bromine at the anode (1).Question 33 · Spec 4.4.3.3 · Aluminium extraction
Why is aluminium extracted by electrolysis? [1 mark]
Answer:It is more reactive than carbon, so it cannot be reduced by carbon.Question 34 · Spec 4.4.3.3 · Aluminium extraction
Why is aluminium oxide mixed with cryolite? [1 mark]
Answer:To lower the melting point, saving energy.Question 35 · Spec 4.4.3.3 · Aluminium extraction
Why must the carbon anodes be replaced regularly? [1 mark]
Answer:Oxygen produced at the anode reacts with the carbon, making carbon dioxide, so the anodes burn away.Question 36 · Spec 4.4.3.4 · Aqueous solutions
What is produced at the cathode in the electrolysis of aqueous solutions? [2 marks]
Answer:The metal, if it is less reactive than hydrogen (1); otherwise hydrogen gas (1).Question 37 · Spec 4.4.3.4 · Aqueous solutions
What is produced at the anode in the electrolysis of aqueous solutions? [2 marks]
Answer:The halogen, if halide ions are present (1); otherwise oxygen (1).Question 38 · Spec 4.4.3.4 · Brine
Name the three products of the electrolysis of sodium chloride solution. [3 marks]
Answer:Hydrogen at the cathode (1); chlorine at the anode (1); sodium hydroxide left in solution (1).Question 39 · Spec 4.4.3.4 · Required practical 3
Describe how to test the gases produced in the electrolysis of an aqueous solution. [2 marks]
Answer:Hydrogen gives a squeaky pop with a lighted splint (1); chlorine bleaches damp litmus paper (oxygen relights a glowing splint) (1).Question 40 · Spec 4.4.3.5 · Half equations · Higher only
Write the half equation at the cathode for the electrolysis of molten aluminium oxide. [1 mark]
Answer:Al³⁺ + 3e⁻ → Al.Question 41 · Spec 4.4.3.5 · Half equations · Higher only
Write the half equation for chloride ions at the anode. [1 mark]
Answer:2Cl⁻ → Cl₂ + 2e⁻.Question 42 · Spec 4.4.3.5 · Half equations · Higher only
Is the reaction at the cathode oxidation or reduction? [1 mark]
Answer:Reduction, because ions gain electrons.Question 43 · Spec 4.4.2.1 · Acids and metals
Why do metals like copper not react with dilute acids? [1 mark]
Answer:Copper is less reactive than hydrogen.Question 44 · Spec 4.4.2.2 · Neutralisation
Write the balanced equation for sodium hydroxide reacting with hydrochloric acid. [1 mark]
Answer:NaOH + HCl → NaCl + H₂O.Question 45 · Spec 4.4.1.2 · Reactivity series
Describe the reaction of potassium with water. [2 marks]
Answer:It reacts very vigorously, catching fire with a lilac flame (1); producing potassium hydroxide and hydrogen (1).Question 46 · Spec 4.4.2.5 · Titration
Why is a pipette used to measure the alkali in a titration? [1 mark]
Answer:It measures a fixed volume very accurately.Question 47 · Spec 4.4.3.2 · Molten compounds
Why must ionic compounds be molten or dissolved for electrolysis? [1 mark]
Answer:The ions must be free to move to the electrodes.Question 48 · Spec 4.4.3.4 · Aqueous solutions
Predict the product at the cathode when copper sulfate solution is electrolysed. [1 mark]
Answer:Copper, because it is less reactive than hydrogen.Question 49 · Spec 4.4.2.4 · Indicators
What colour is universal indicator in a neutral solution? [1 mark]
Answer:Green.Question 50 · Spec 4.4.3.3 · Aluminium extraction
Why is extracting aluminium expensive? [1 mark]
Answer:It uses large amounts of electricity to melt the ore and to carry out electrolysis.