Redox, Metals and ElectrolysisIB MYP Chemistry: Topic test

20 questions, 54 marks

IB MYP Chemistry

Redox, Metals and Electrolysis topic test

Total 54 marks

Name

Class

Date

1
In a demonstration in Toronto, a teacher lowers a piece of hot sodium into a gas jar of chlorine. The sodium burns with a bright yellow flame and white smoke of sodium chloride forms. The teacher writes the equation 2Na + Cl₂ → 2NaCl and explains that each sodium atom becomes a Na⁺ ion.
(a)
What happens to each sodium atom in this reaction?
[1 mark]
AIt gains one electron and is oxidised
BIt loses one electron and is oxidised
CIt gains one electron and is reduced
DIt loses one electron and is reduced
(b)
Which substance is the oxidising agent in this reaction?
[1 mark]
AChlorine, because it gains electrons from the sodium
BChlorine, because it loses electrons to the sodium
CSodium, because it loses electrons
DSodium chloride, because it is the product
(c)
Write the half-equation for the change that happens to the sodium, and explain why this change is oxidation.
[2 marks]
Total for question 1: 4 marks
2
A jeweller in Istanbul places a clean copper wire in a colourless solution of silver nitrate. Over an hour, grey-silver crystals grow on the wire and the solution slowly turns blue.
(a)
Which statement explains why the solution turns blue?
[1 mark]
ASilver is more reactive than copper, so silver atoms form blue ions
BCopper atoms gain electrons and form blue copper(II) ions
CCopper atoms lose electrons and form blue copper(II) ions in the solution
DSilver ions lose electrons and form blue silver atoms
(b)
Which metal could NOT displace silver from silver nitrate solution?
[1 mark]
AMagnesium
BZinc
CIron
DGold
(c)
Copper forms copper(II) nitrate, Cu(NO₃)₂, in this reaction and the silver crystals are Ag. Write a balanced symbol equation for the reaction.
[2 marks]
Total for question 2: 4 marks
3
Students at a school in Colombo, which is near the sea, want to find out whether salt affects how quickly iron rusts. They clean four identical iron nails with sandpaper and put each nail in its own beaker. Each beaker holds 100 cm³ of tap water, with 0 g, 1 g, 2 g or 4 g of salt dissolved in it. The beakers are left in the same room for one week and the nails are then examined for rust.
(a)
State a hypothesis for this investigation, with a scientific reason, and identify the independent variable.
[3 marks]
(b)
Describe the dependent variable and one way to measure it, name two control variables, and give one safety precaution.
[4 marks]
Total for question 3: 7 marks
4
A metals company in Lima produces two metals. Zinc is made by heating zinc oxide, ZnO, with carbon in a furnace. Aluminium is made by passing electricity through molten aluminium oxide, Al₂O₃, dissolved in cryolite. The company also plans to build a plant that recycles scrap zinc and aluminium from old products.
(a)
Explain, using the reactivity series and ideas of oxidation and reduction, why zinc oxide can be reduced by heating with carbon but aluminium oxide has to be electrolysed.
[6 marks]
(b)
Discuss the benefits and drawbacks of recycling scrap zinc and aluminium instead of extracting the metals from their ores, and reach a justified conclusion.
[6 marks]
Total for question 4: 12 marks
5
In a laboratory in Perth, students electrolyse water that contains a little dilute sulfuric acid, using inert platinum electrodes. Gas bubbles form at both electrodes and are collected in separate tubes. One tube collects twice as much gas as the other.
(a)
Which gas collects in the larger volume, and at which electrode?
[1 mark]
AHydrogen at the cathode
BHydrogen at the anode
COxygen at the cathode
DOxygen at the anode
(b)
Why is dilute sulfuric acid added to the water?
[1 mark]
AIt is the substance that is split into hydrogen and oxygen
BIt is used to make the electrodes inert
CIt provides ions so that the liquid conducts electricity
DIt cools the electrodes during the experiment
(c)
Write the half-equation for the reaction at the cathode and state why it is a reduction.
[2 marks]
Total for question 5: 4 marks
6
A student in Lisbon builds three cells. Each cell has two different metal strips dipped in the same beaker of sodium sulfate solution and joined to a voltmeter by wires. Cell 1 uses magnesium and zinc, Cell 2 uses zinc and iron, and Cell 3 uses magnesium and iron. The voltmeter reads about 1.5 V for Cell 1, 0.3 V for Cell 2 and 1.8 V for Cell 3.
(a)
In Cell 3, which is the correct direction of electron flow?
[1 mark]
AFrom the iron to the magnesium through the wires
BFrom the magnesium to the iron through the solution
CFrom the iron to the magnesium through the solution
DFrom the magnesium to the iron through the wires
(b)
The student then makes Cell 4 using magnesium and copper in the same solution. Which prediction is best?
[1 mark]
AA voltage lower than 1.8 V, because copper is less reactive than iron
BA voltage higher than 1.8 V, because copper is further below magnesium in the reactivity series than iron
CA voltage of exactly 1.8 V, because both iron and copper are less reactive than magnesium
DNo voltage, because copper does not react with the solution
(c)
Explain why a cell made from two strips of the same metal gives no voltage.
[2 marks]
Total for question 6: 4 marks
7
Students in Hanoi copper-plate identical steel keys. Each key is the cathode in a copper(II) sulfate solution with a copper anode, and the current is kept at 0.50 A. A key is weighed before and after plating for different times. The mass of copper gained is 0.05 g after 5 minutes, 0.10 g after 10 minutes, 0.15 g after 15 minutes, 0.20 g after 20 minutes and 0.31 g after 25 minutes. The students' hypothesis is that the mass of copper deposited is proportional to the time.
(a)
Describe the relationship between time and mass of copper for the first four results, and calculate the mass of copper deposited per minute using the 20-minute result.
[3 marks]
(b)
Evaluate the investigation: identify the anomalous result and explain why it is anomalous, suggest one cause, suggest one improvement, and state whether the results support the students' hypothesis.
[4 marks]
Total for question 7: 7 marks
8
Wind turbines in the North Sea off Denmark stand on steel foundations that are partly underwater, where seawater supplies salts, oxygen and water. Engineers bolt large blocks of zinc to each steel foundation. Divers replace the blocks every few years. The wind company has asked a panel to explain how the blocks work and to evaluate the design.
(a)
Explain how the zinc blocks stop the steel foundations from rusting, using ideas of reactivity, oxidation and electron flow.
[6 marks]
(b)
Discuss the benefits and drawbacks of protecting the foundations with zinc blocks, and reach a justified conclusion.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).