Chemical ChangesOxford AQA IGCSE Chemistry: Topic test

20 questions, 54 marks

Oxford AQA IGCSE Chemistry

Chemical Changes topic test

Total 54 marks

Name

Class

Date

1
An engineer tests three metal samples, magnesium, zinc and copper, by adding a piece of each to separate test tubes of dilute hydrochloric acid of the same concentration, and timing how vigorously each one reacts.
(a)
Which metal is expected to react most vigorously with the dilute hydrochloric acid?
[1 mark]
AMagnesium
BZinc
CCopper
DNone of the metals will react
(b)
Which metal is expected to show no visible reaction at all with the acid?
[1 mark]
AMagnesium
BCopper
CZinc
DAll three metals react equally
(c)
Explain, in terms of electron loss, why magnesium reacts more vigorously with the acid than zinc, and why copper does not react at all.
[2 marks]
Total for question 1: 4 marks
2
A student places a coil of iron wire into a colourless solution of silver nitrate. Over several minutes, silvery crystals form on the iron wire, and the solution slowly turns pale green.
(a)
What type of reaction is taking place between the iron wire and the silver nitrate solution?
[1 mark]
ANeutralisation
BThermal decomposition
CDisplacement
DElectrolysis
(b)
Which species gains electrons (is reduced) in this reaction?
[1 mark]
AIron atoms
BNitrate ions
CIron ions
DSilver ions
(c)
Write the ionic equation for this reaction, and state which species is oxidised.
[2 marks]
Total for question 2: 4 marks
3
A technician heats separate samples of lithium carbonate and potassium carbonate, both to the same high temperature reached by a Bunsen burner, and observes the results.
(a)
Predict what happens when each sample is heated strongly with a Bunsen burner, and explain the difference between them.
[3 marks]
(b)
The potassium carbonate sample, which does not decompose on heating, is instead reacted with dilute nitric acid. Describe what would be observed, and write a word equation for the reaction.
[4 marks]
Total for question 3: 7 marks
4
A geology student is comparing three metals found in different states in the Earth's crust: silver, which is found as the uncombined metal in some ore deposits; zinc, which is found combined as zinc oxide and can be reduced using carbon; and aluminium, which is found combined as aluminium oxide but cannot be extracted using carbon.
(a)
Explain, using ideas about reactivity, why silver, zinc and aluminium each require a different method of extraction (or, for silver, no chemical extraction at all).
[6 marks]
(b)
Explain why extracting aluminium by electrolysis is much more expensive than extracting zinc by reduction with carbon, and describe how the extraction process for aluminium is designed to reduce this cost.
[6 marks]
Total for question 4: 12 marks
5
An orthodontist selects a nickel-titanium alloy wire, rather than a wire of pure titanium, for a dental brace, because the alloy wire is more flexible and can be bent into shape while still gently pulling teeth back into their correct position over time.
(a)
What makes the nickel-titanium wire an alloy?
[1 mark]
AIt is a mixture of at least two elements, nickel and titanium, both of which are metals
BIt contains only nickel atoms
CIt is a compound formed from nickel and titanium in a fixed chemical ratio
DIt does not contain any metal atoms
(b)
Why might the alloy have different properties from pure titanium?
[1 mark]
AMixing different-sized metal atoms disrupts the regular layers of a pure metal, changing how the layers slide over each other and altering its properties
BAlloys are always weaker than the pure metals they are made from
CAlloys cannot conduct electricity, unlike pure metals
DAlloys have no metallic bonding at all
(c)
Explain, in general terms, why alloys often have different, more useful properties than the pure metals they are made from.
[2 marks]
Total for question 5: 4 marks
6
A clothing manufacturer wants to electroplate brass buttons, used on a range of jeans, with a thin, decorative layer of gold, to improve their appearance without using expensive solid gold.
(a)
In the electroplating cell, what should the brass button be connected to?
[1 mark]
AThe positive electrode (anode)
BNeither electrode; it is placed in the solution unconnected
CThe negative electrode (cathode)
DBoth electrodes at once
(b)
What should the electrolyte solution in the cell contain?
[1 mark]
AA solution containing gold ions
BPure water with no dissolved ions
CA solution containing brass ions only
DConcentrated hydrochloric acid
(c)
Explain why electroplating is used on the brass buttons rather than making them from solid gold.
[2 marks]
Total for question 6: 4 marks
7
A recycling company compares the amount of electrical energy needed to produce 1 tonne of aluminium from bauxite ore by electrolysis, with the energy needed to produce 1 tonne of aluminium from recycled aluminium scrap by simply melting it down and reshaping it.
(a)
Explain why producing aluminium from recycled scrap requires far less energy than producing it from bauxite ore by electrolysis.
[3 marks]
(b)
Explain, using ideas about reactivity, why aluminium cannot be extracted from its ore by heating aluminium oxide with carbon, unlike some other metals, and explain the wider benefit of recycling aluminium instead of extracting it from ore each time.
[4 marks]
Total for question 7: 7 marks
8
A chemical plant operates two separate electrolysis cells at the same time. Cell 1 contains copper(II) sulfate solution with copper electrodes, used to purify copper. Cell 2 contains concentrated sodium chloride solution (brine) with inert electrodes, used to produce industrial chemicals.
(a)
Describe the products formed at each electrode in Cell 1 and in Cell 2, explaining why the products differ between the two cells.
[6 marks]
(b)
State the industrial importance of the products formed in Cell 2, and explain why copper electrodes in Cell 1 behave so differently from the inert electrodes used in Cell 2.
[6 marks]
Total for question 8: 12 marks

End of questions