Pearson Edexcel GCSE Combined Science · C3

Chemical change

Revision questions with answers for C3 Chemical change in Pearson Edexcel GCSE Combined Science (spec 1SC0). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below.

All questions and answers

Question 1 · Spec C3.1
Which ions do acids and alkalis provide in water?
Answer:
Acids provide H⁺ ions; alkalis provide OH⁻ ions.
Question 2 · Spec C3.2
How does pH classify an aqueous solution?
Answer:
Below 7 is acidic; 7 is neutral; above 7 is alkaline.
Question 3 · Spec C3.3
How does litmus behave in acids and alkalis?
Answer:
It is red in acid and blue in alkali.
Question 4 · Spec C3.3
What colours does methyl orange show in acid and alkali?
Answer:
Red in acid and yellow in alkali.
Question 5 · Spec C3.3
What colours does phenolphthalein show in acid and alkali?
Answer:
Colourless in acid and pink in alkali.
Question 6 · Spec C3.4 · Higher only
How does increasing hydrogen ion concentration affect pH?
Answer:
It lowers pH; increasing hydroxide ion concentration in an alkaline solution raises pH.
Question 7 · Spec C3.5 · Higher only
How much higher is hydrogen ion concentration at pH 2 than pH 4?
Answer:
100 times higher: a tenfold increase for each one-unit fall.
Question 8 · Spec C3.7 · Higher only
What do dilute and concentrated describe?
Answer:
The amount of dissolved substance per volume of solution, not its degree of ionisation.
Question 9 · Spec C3.8 · Higher only
How do strong and weak acids differ?
Answer:
Strong acids dissociate essentially completely in water; weak acids dissociate only partly.
Question 10 · Spec C3.9
How do a base and an alkali differ?
Answer:
A base reacts with acid to form salt and water only; an alkali is a soluble base.
Question 11 · Spec C3.13
What is neutralisation?
Answer:
Reaction of an acid with a base to form a salt and water.
Question 12 · Spec C3.14
What occurs between H⁺ and OH⁻ during neutralisation?
Answer:
They react to form water: H⁺ + OH⁻ → H₂O.
Question 13 · Spec C3.11
What are the general products of a reactive metal and dilute acid?
Answer:
A salt and hydrogen gas.
Question 14 · Spec C3.11
What are the general products of a metal carbonate and acid?
Answer:
A salt, water and carbon dioxide.
Question 15 · Spec C3.11
Which salts are formed by hydrochloric, sulfuric and nitric acids?
Answer:
Chlorides, sulfates and nitrates, respectively.
Question 16 · Spec C3.12
How is hydrogen identified?
Answer:
A lighted splint gives a squeaky pop.
Question 17 · Spec C3.12
How is carbon dioxide identified using limewater?
Answer:
Bubble the gas through it; limewater becomes milky or cloudy.
Question 18 · Spec C3.15
Outline preparing a soluble salt using an insoluble base.
Answer:
React excess base with acid, filter off unreacted solid, then concentrate and crystallise the salt solution.
Question 19 · Spec C3.6 · Core practical
What should be controlled when investigating pH change as calcium oxide or hydroxide is added?
Answer:
Use a fixed acid volume and concentration, consistent powder additions and mixing, and the same calibrated pH measurement method.
Question 20 · Spec C3.6 · Core practical
Outline investigating pH while adding calcium oxide or hydroxide to hydrochloric acid.
Answer:
Measure initial acid pH, add small measured amounts of powder, stir, allow reaction and record pH after each addition.
Question 21 · Spec C3.17 · Core practical
Why warm sulfuric acid in a water bath before adding copper oxide?
Answer:
Gentle controlled warming speeds the reaction without direct strong heating of the acid.
Question 22 · Spec C3.17 · Core practical
How are pure dry hydrated copper sulfate crystals obtained after filtration?
Answer:
Concentrate gently, cool to crystallise, filter the crystals and dry them without strong heating.
Question 23 · Spec C3.16
Why is titration needed when both salt-making reactants are soluble?
Answer:
Excess acid or alkali cannot be removed by filtration, so correct reacting proportions must be measured.
Question 24 · Spec C3.18
Describe an acid-alkali titration.
Answer:
Pipette a measured solution volume into a flask; add indicator; deliver the other solution from a burette to the endpoint and record volume.
Question 25 · Spec C3.18
How can a titration be used to prepare a pure salt without indicator contamination?
Answer:
Find the reacting volumes, then repeat with those volumes without indicator and crystallise the resulting solution.
Question 26 · Spec C3.19
Which sodium, potassium and ammonium salts are soluble?
Answer:
All common salts of these ions.
Question 27 · Spec C3.19
Which nitrates are soluble?
Answer:
All common nitrates.
Question 28 · Spec C3.19
What are the main exceptions to chloride solubility?
Answer:
Silver chloride and lead chloride are insoluble in the GCSE rules.
Question 29 · Spec C3.19
What are the main exceptions to sulfate solubility?
Answer:
Lead, barium and calcium sulfates.
Question 30 · Spec C3.19
What is the general rule for carbonates and hydroxides?
Answer:
They are generally insoluble except the common sodium, potassium and ammonium compounds in the specified rules.
Question 31 · Spec C3.20
What precipitate forms when silver nitrate and sodium chloride solutions mix?
Answer:
Silver chloride; sodium nitrate remains dissolved.
Question 32 · Spec C3.21
How is a pure dry insoluble salt prepared?
Answer:
Mix suitable soluble reactants, filter the precipitate, wash with pure water and dry it.
Question 33 · Spec C3.22
What is an electrolyte?
Answer:
An ionic compound molten or dissolved in water, with ions free to move.
Question 34 · Spec C3.23
What happens during electrolysis?
Answer:
Electrical energy from a direct-current supply decomposes an electrolyte at its electrodes.
Question 35 · Spec C3.24
Where do cations and anions move during electrolysis?
Answer:
Positive cations move to the negative cathode; negative anions move to the positive anode.
Question 36 · Spec C3.25
What forms from copper chloride solution with inert electrodes?
Answer:
Copper at the cathode and chlorine at the anode.
Question 37 · Spec C3.25
What forms when concentrated sodium chloride solution is electrolysed with inert electrodes?
Answer:
Hydrogen at the cathode and chlorine at the anode.
Question 38 · Spec C3.25
What forms from sodium sulfate solution with inert electrodes?
Answer:
Hydrogen at the cathode and oxygen at the anode.
Question 39 · Spec C3.25
What forms from water acidified with sulfuric acid during electrolysis?
Answer:
Hydrogen at the cathode and oxygen at the anode, with about twice the hydrogen volume.
Question 40 · Spec C3.26
Predict products from molten lead bromide.
Answer:
Lead at the cathode and bromine at the anode.
Question 41 · Spec C3.27 · Higher only
Write the half equation for copper deposition.
Answer:
Cu²⁺ + 2e- → Cu.
Question 42 · Spec C3.27 · Higher only
Write the half equation for chloride forming chlorine.
Answer:
2Cl⁻ → Cl₂ + 2e-.
Question 43 · Spec C3.29 · Higher only
Which electrode reactions are oxidation and reduction?
Answer:
Reduction, electron gain, occurs at the cathode; oxidation, electron loss, occurs at the anode.
Question 44 · Spec C3.30
How can copper-electrode electrolysis purify copper?
Answer:
Impure copper is the anode and pure copper the cathode; copper dissolves from the anode and is deposited at the cathode.
Question 45 · Spec C3.31 · Core practical
What forms at inert electrodes in copper sulfate solution?
Answer:
Copper at the cathode and oxygen at the anode.
Question 46 · Spec C3.31 · Core practical
How do copper electrodes change copper sulfate electrolysis?
Answer:
The copper anode dissolves instead of producing oxygen; copper deposits on the cathode.
Question 47 · Spec C3.31 · Core practical
How can mass changes of copper electrodes be measured?
Answer:
Clean, dry and weigh them before and after a controlled electrolysis period.
Question 48 · Spec C3.31 · Core practical
Which variables should be controlled when comparing electrodes?
Answer:
Current or supply setting, time, electrode area and solution volume and concentration.
Question 49 · Spec C3.6 · Core practical
How should pH change as calcium oxide or hydroxide is added to dilute hydrochloric acid?
Answer:
It rises from acidic towards neutral; sufficient excess base makes the solution alkaline.
Question 50 · Spec C3.25
Why can aqueous and molten electrolytes give different products?
Answer:
Aqueous solutions also contain ions from water, which can be discharged instead of the compound's ions.

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Chemical change

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