R3.2 Electron transfer reactions
Practice exam-style IB Chemistry questions for Electron transfer reactions, aligned with the syllabus and grouped by topic.
Question 1
What describes oxidation in terms of electron transfer?
A.
Decrease in oxidation state of a species
B.
Loss of electrons by a species
C.
Gain of electrons by a species
D.
Gain of hydrogen by a species
Question 2
What is the oxidation state of sulfur in SO4^2-?
A.
+4
B.
+2
C.
+8
D.
+6
Question 3
In the reaction Zn
A.
Cu2+(aq)
B.
Zn(s)
C.
Cu(s)
D.
Zn2+(aq)
Question 4
Molten lead(II) bromide is electrolysed using inert electrodes. What forms at the cathode and anode?
A.
Cathode: Pb; anode: Br2
B.
Cathode: Pb; anode: O2
C.
Cathode: Br2; anode: Pb
D.
Cathode: H2; anode: Br2
Question 5
But-2-yne reacts with one mole of hydrogen. What type of product is formed?
A.
A ketone
B.
An alkene
C.
An alkane
D.
An alcohol
Question 6
What is the standard electrode potential assigned to the standard hydrogen electrode?
A.
+0.34 V
B.
0.00 V
C.
-1.00 V
D.
+1.00 V
Question 7
A steel key is to be copper-plated. What role must the key have in the electrolytic cell?
A.
Electrolyte, where electrons are conducted
B.
Salt bridge, where ions migrate
C.
Cathode, where copper ions are reduced
D.
Anode, where copper is oxidized
Question 8
Magnesium reacts with dilute sulfuric acid.
Write the balanced equation.
[1]
State the test and positive result for the gas produced.
[1]
Question 9
A voltaic cell has oxidation occurring at the zinc electrode and reduction at the silver electrode. What are the signs of the electrodes?
A.
Zinc positive; silver negative
B.
Both electrodes negative
C.
Both electrodes positive
D.
Zinc negative; silver positive
Question 10
In a Zn
A.
From zinc to copper
B.
From copper to zinc
C.
From copper ions to zinc ions
D.
From the salt bridge to zinc
Question 11
Propan-1-ol is heated under reflux with excess oxidizing agent. What is the main organic product?
A.
Propane
B.
Propanone
C.
Propanoic acid
D.
Propanal
Question 12
The standard reduction potentials are Ag+(aq)/Ag
A.
-0.36 V
B.
+1.24 V
C.
+0.36 V
D.
-1.24 V
Question 13
A proposed reaction has E standard cell = -0.27 V. What is correct under standard conditions?
A.
The forward reaction is spontaneous.
B.
No redox reaction can occur in either direction.
C.
The reaction is at equilibrium.
D.
The reverse reaction is spontaneous.
Question 14
Concentrated aqueous sodium chloride is electrolysed using inert electrodes. What are the main products at the cathode and anode?
A.
Cathode: hydrogen; anode: chlorine
B.
Cathode: sodium; anode: chlorine
C.
Cathode: sodium; anode: oxygen
D.
Cathode: hydrogen; anode: oxygen
Question 15
Aqueous copper(II) sulfate is electrolysed using inert platinum electrodes. What forms at the anode?
A.
Copper metal
B.
Sulfur dioxide gas
C.
Hydrogen gas
D.
Oxygen gas
Question 16
What does a more positive standard reduction potential indicate for the species on the left of a reduction half-equation?
A.
It is more easily reduced and is a stronger oxidizing agent.
B.
It has a lower concentration at equilibrium.
C.
It transfers fewer electrons in the half-equation.
D.
It is more easily oxidized and is a stronger reducing agent.
Question 17
Consider the reaction: 2FeCl2(aq) + Cl2(aq) -> 2FeCl3(aq).
State the oxidation state of iron in FeCl2 and FeCl3.
[1]
Identify the oxidizing agent.
[1]
Question 18
A strip of metal X is placed in a solution of Y2+(aq). A coating of metal Y forms on X.
State which metal, X or Y, is more easily oxidized.
[1]
Explain your answer using electron transfer.
[1]
Question 19
During discharge of a simplified secondary cell, the cathode reaction is M3+(aq) + e- -> M2+(aq).
State the type of reaction at the cathode during discharge.
[1]
Deduce the corresponding half-equation during charging.
[1]
Question 20
Molten calcium chloride is electrolysed using inert electrodes.
Write the cathode half-equation.
[1]
Explain why solid calcium chloride does not conduct electricity.
[1]
Question 21
The standard hydrogen electrode is used to measure standard electrode potentials.
State two standard conditions used for the electrode.
[1]
State the role of platinum.
[1]
Question 22
Concentrated and dilute aqueous sodium chloride are electrolysed using inert electrodes.
State the main anode product for concentrated sodium chloride solution.
[1]
Explain why the anode product may differ for dilute sodium chloride solution.
[1]
Question 23
A spoon is silver-plated using a silver anode and a solution containing Ag+(aq).
Identify the electrode to which the spoon is connected.
[1]
Write the half-equation at the spoon.
[1]
State the mass change of the silver anode.
[1]
Question 24
A student placed strips of metals A, B and C into solutions containing A2+, B2+ and C2+ ions. A tick in the table shows that a visible metal coating formed.
| Metal strip | Ion solution | Coating formed |
|---|---|---|
| A | B2+(aq) | ✓ |
| A | C2+(aq) | ✓ |
| B | A2+(aq) | ✗ |
| B | C2+(aq) | ✓ |
| C | A2+(aq) | ✗ |
| C | B2+(aq) | ✗ |
State which metal is most easily oxidized.
[1]
Deduce the order of ease of oxidation of A, B and C, from greatest to least.
[1]
Explain why a coating forms when metal B is placed in C2+(aq).
[1]
Question 25
The diagram shows a voltaic cell made from aluminium and nickel half-cells. The overall reaction is 2Al
- 3Ni2+(aq) -> 2Al3+(aq) + 3Ni(s).
[1]
Identify the anode.
[1]
Draw or state the direction of electron flow in the external circuit.
[1]
State the direction of anion movement in the salt bridge and explain why.
[1]
Question 26
The graph shows the masses of the products collected during electrolysis of a molten binary salt, QBr2, using inert electrodes.
Identify the electrode at which Q forms.
[1]
Write the half-equation for formation of bromine.
[1]
Explain why the electrolyte must be molten.
[1]
Question 27
For a redox reaction, n = 2 and E standard cell = +1.10 V. Using F = 9.65 x 10^4 C mol^-1, what is Delta G standard?
A.
+212 kJ mol^-1
B.
-106 kJ mol^-1
C.
-212 kJ mol^-1
D.
+106 kJ mol^-1
Question 28
In acidic solution, MnO4-(aq) is reduced to Mn2+(aq).
State where electrons appear in a reduction half-equation.
[1]
Deduce the balanced half-equation.
[1]
Question 29
A voltaic cell is made from Mg
(s)|Mg2+(aq) and Cu2+(aq)|Cu(s). Magnesium is oxidized.
[1]
Identify the anode.
[1]
State the direction of electron flow.
[1]
Explain one role of the salt bridge.
[1]
Question 30
Butan-2-ol is oxidized using an appropriate oxidizing agent. Ethanal is reduced using a reducing agent represented by [H].
Give the organic product from butan-2-ol.
[1]
Write the equation for the reduction of ethanal.
[1]
Question 31
Use the standard reduction potentials: Cu2+(aq) + 2e- ⇌ Cu
(s), E standard = +0.34 V; Sn2+(aq) + 2e- ⇌ Sn(s), E standard = -0.14 V.
[1]
Identify the cathode in the spontaneous cell.
[1]
Calculate E standard cell.
[1]
Question 32
For a reaction with E standard cell = +0.52 V, two moles of electrons are transferred per mole of reaction. Use F = 9.65 x 10^4 C mol^-1.
Calculate Delta G standard in kJ mol^-1.
[1]
State whether the reaction is spontaneous under standard conditions.
[1]
Question 33
Aqueous copper(II) sulfate is electrolysed using inert graphite electrodes.
Write the cathode half-equation.
[1]
Write the anode half-equation.
[1]
State the visible change in the blue solution during electrolysis.
[1]
Question 34
Aqueous copper(II) sulfate is electrolysed first with inert electrodes and then with copper electrodes.
Compare the anode reactions.
[1]
Compare the change in Cu2+(aq) concentration.
[1]
Question 35
A solution containing Fe2+(aq) was titrated with acidified MnO4-(aq). The graph shows the volume of MnO4-(aq) added against colour intensity of the solution.
Identify the endpoint from the graph.
[1]
Explain why no separate indicator is needed.
[1]
Write the oxidation half-equation for Fe2+(aq).
[1]
Question 36
A primary alcohol was oxidized using two apparatus arrangements shown in the figure. The table gives the main organic product collected in each arrangement.
Identify which arrangement is reflux.
[1]
Deduce the product expected under reflux.
[1]
Explain why distillation can give an aldehyde as the main product.
[1]
Suggest one reason for using excess oxidizing agent in reflux.
[1]
Question 37
The table gives standard reduction potentials for three half-cells.
| Reduction half-equation | E° / V |
|---|---|
| X²⁺(aq) + 2e⁻ → X(s) | −0.44 |
| Y⁺(aq) + e⁻ → Y(s) | +0.16 |
| Z²⁺(aq) + 2e⁻ → Z(s) | +0.68 |
Identify the strongest oxidizing agent.
[1]
Calculate E standard cell for the spontaneous cell using X2+/X and Z2+/Z.
[1]
Write the overall equation for this cell.
[1]
Question 38
A copper electroplating experiment used a copper anode and a steel object as the cathode in copper(II) sulfate solution. The graph shows the masses of both electrodes during electrolysis.
Identify the curve for the cathode.
[1]
Write the anode half-equation.
[1]
Explain why the Cu2+(aq) concentration remains nearly constant.
[1]
Question 39
The standard reduction potentials of two half-cells are: A2+(aq) + 2e- ⇌ A
(s), E standard = -1.66 V; B2+(aq) + 2e- ⇌ B(s), E standard = +0.76 V.
[1]
Identify the stronger oxidizing agent.
[1]
Identify the stronger reducing agent.
[1]
Explain one choice.
[1]
Question 40
The graph shows Delta G standard calculated for several electrochemical reactions plotted against E standard cell. All reactions transfer two moles of electrons.
Describe the relationship shown.
[1]
Calculate the gradient expected using F = 9.65 x 10^4 C mol^-1.
[1]
Explain the significance of the sign of Delta G standard for a reaction with positive E standard cell.
[1]
Question 41
Aqueous solutions were electrolysed using inert electrodes. The table lists the ions present and selected standard reduction potentials.
| Solution | Aqueous ions | Electrodes | Reduction half-equation | E° / V |
|---|---|---|---|---|
| I | Na+(aq), Cl−(aq) | inert | Na+(aq) + e− → Na(s) | −2.71 |
| I | Na+(aq), Cl−(aq) | inert | 2H2O(l) + 2e− → H2(g) + 2OH−(aq) | −0.83 |
| II | Cu2+(aq), SO4^2−(aq) | inert | Cu2+(aq) + 2e− → Cu(s) | +0.34 |
| II | Cu2+(aq), SO4^2−(aq) | inert | 2H2O(l) + 2e− → H2(g) + 2OH−(aq) | −0.83 |
Deduce the cathode product for solution I containing NaCl(aq).
[1]
Deduce the cathode product for solution II containing CuSO4(aq).
[1]
Explain the different cathode products using the data.
[1]
Question 42
Iron reacts with acidified dichromate(VI) ions as follows: Cr2O7^2-(aq) + Fe2+(aq) + H+(aq) -> Cr3+(aq) + Fe3+(aq) + H2O
(l).
[1]
Determine the oxidation states of chromium in Cr2O7^2- and Cr3+.
[1]
Explain, using half-equations, how the overall redox equation is balanced in acidic solution.
[1]
Question 43
Alcohols may undergo oxidation depending on their structure and the conditions used.
State the oxidation products of a primary alcohol under distillation and under reflux.
[1]
Compare the oxidation of primary, secondary and tertiary alcohols, including equations using [O] where appropriate.
[1]
Question 44
Electrochemical cells include primary cells, secondary cells and fuel cells.
Define a secondary cell and a fuel cell.
[1]
Discuss advantages and disadvantages of primary cells, secondary cells and hydrogen fuel cells.
[1]
Question 45
A student measured the standard electrode potential of a metal M2+(aq)/M
| Trial | Voltmeter reading / V |
|---|---|
| 1 | 0.74 |
| 2 | 0.75 |
| 3 | 0.76 |
| 4 | 0.75 |
| 5 | 0.74 |
half-cell against the standard hydrogen electrode. The voltmeter readings for repeated trials are shown in the table. The metal electrode was negative relative to the hydrogen electrode.
[1]
Determine E standard for M2+(aq)/M(s).
[1]
State the electrode at which oxidation occurs.
[1]
Evaluate whether the data support M
[1]
being a stronger reducing agent than H2(g).
[1]
Question 46
A primary cell is constructed from Zn
(s)|Zn2+(aq) and Ag+(aq)|Ag(s). Zinc is oxidized and silver ions are reduced.
[1]
Write the two half-equations and the overall equation.
[1]
Explain how this cell produces an electric current, including electrode signs, electron flow and salt bridge ion movement.
[1]
Question 47
The standard reduction potentials are: Br2(aq) + 2e- ⇌ 2Br-(aq), E standard = +1.07 V; Fe3+(aq) + e- ⇌ Fe2+(aq), E standard = +0.77 V; I2(aq) + 2e- ⇌ 2I-(aq), E standard = +0.54 V.
Identify the strongest oxidizing agent and strongest reducing agent in the data.
[1]
Evaluate whether Fe3+(aq) can oxidize I-(aq) and whether Br-(aq) can reduce Fe3+(aq), using E standard cell values.
[1]
Question 48
Aqueous sodium chloride and molten sodium chloride are each electrolysed using inert electrodes.
Deduce the products of electrolysis of molten sodium chloride and give the half-equations.
[1]
Explain why the products differ for concentrated aqueous sodium chloride and write the overall equation for the aqueous process.
[1]
Question 49
A manufacturer wants to nickel-plate a steel component using an electrolytic cell with a nickel anode and Ni2+(aq) electrolyte.
Draw or describe the essential arrangement for nickel electroplating.
[1]
Evaluate how the electrode reactions affect the masses of the electrodes and the concentration of Ni2+(aq), and suggest one practical factor needed for an even coating.
[1]
Question 50
A voltaic cell is based on the reaction Zn
- Cu2+(aq) -> Zn2+(aq) + Cu(s). Standard reduction potentials are Zn2+(aq)/Zn
[1]
= -0.76 V and Cu2+(aq)/Cu
[1]
= +0.34 V.
[1]
Calculate E standard cell and Delta G standard for the reaction, using F = 9.65 x 10^4 C mol^-1.
[1]
Discuss what the signs of E standard cell and Delta G standard indicate, and explain why E standard values are not multiplied when the half-equations are balanced.
[1]
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