IBDP Official Exam Material
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Topic 19: Redox Processes
For HL students only
1. [1 mark]
The standard electrode potentials for three half-cells involving chromium are shown.
Cr3+ (aq) + e− ⇌ Cr2+ (aq) E⦵ = −0.407 V
Cr3+ (aq) + 3e− ⇌ Cr (s) E⦵ = −0.744 V
Cr2+ (aq) + 2e− ⇌ Cr (s) E⦵ = −0.914 V
Which statement is correct?
A. Cr3+ (aq) can oxidize Cr2+ (aq) but not Cr (s).
A. Cr3+ (aq) can oxidize Cr2+ (aq) but not Cr (s).
B. Cr3+ (aq) can oxidize Cr (s) but not Cr2+ (aq).
C. Cr3+ (aq) can oxidize both Cr2+ (aq) and Cr (s).
D. Cr3+ (aq) can oxidize Cr (s) and reduce Cr2+ (aq).
2. [1 mark]
Which factors affect the amount, in mol, of product formed during electrolysis?
I. The charge on the ion
II. The molar mass of the ion
III. The duration of the electrolysis
A. I and II only
II. The molar mass of the ion
III. The duration of the electrolysis
A. I and II only
B. I and III only
C. II and III only
D. I, II and III
3a. [1 mark]
Consider the following reaction:
Cu2+ (aq) + Fe (s) → Fe2+ (aq) + Cu (s)
State the ground-state electron configuration for Fe2+.
3b. [2 marks]
The diagram shows an unlabelled voltaic cell for the reaction:
Cu2+ (aq) + Fe (s) → Fe2+ (aq) + Cu (s)
3c. [1 mark]
Write the half-equation for the reaction occurring at the anode (negative electrode).
3d. [1 mark]
The diagram includes a salt bridge that is filled with a saturated solution of KNO3. Outline the function of the salt bridge.
3h. [2 marks]
Predict the movement of all ionic species through the salt bridge.
3i. [1 mark]
Calculate the standard cell potential, in V, for this cell. Use section 24 of the data booklet.
3j. [1 mark]
Calculate the standard free energy change, in kJ, for the cell. Use your answer in (f)(v) and sections 1 and 2 of the data booklet.
If you did not obtain an answer in (f)(v), use 0.68 V, although this is not the correct answer.
4. [1 mark]
What are the products when dilute aqueous copper (II) nitrate is electrolysed using platinum electrodes?
E⦵ (Cu | Cu2+) = –0.34 V.
5. [1 mark]
In the electrolysis apparatus shown, 0.59 g of Ni is deposited on the cathode of the first cell.
What is the mass of Ag deposited on the cathode of the second cell?
A. 0.54 g
B. 0.59 g
C. 1.08 g
D. 2.16 g
6. [1 mark]
Which E⦵ value, in V, for the reaction Mn (s) + Zn2+ (aq) → Mn2+ (aq) + Zn (s) can be deduced from the following equations?
Mn (s) + 2Ag+ (aq) → Mn2+ (aq) + 2Ag (s) E⦵ = 1.98 V
Zn (s) + Cu2+ (aq) → Zn2+ (aq) + Cu (s) E⦵ = 1.10 V
Cu (s) + 2Ag+ (aq) → Cu2+ (aq) + 2Ag (s) E⦵ = 0.46 V
A. 0.42
B. 1.34
C. 2.62
D. 3.54
7. [1 mark]
What is the order of increasing mass deposited by this electrolytic cell?
Ar Ag = 108, Cu = 64, Sb = 122
A. Ag < Cu < Sb
B. Sb < Ag < Cu
C. Cu < Ag < Sb
D. Cu < Sb < Ag
8a. [2 marks]
Magnesium is a reactive metal often found in alloys.
Suggest an experiment that shows that magnesium is more reactive than zinc, giving the observation that would confirm this.
8b. [1 mark]
Magnesium is sometimes used as a sacrificial anode to protect steel from corrosion.
Calculate the standard potential, in V, of a cell formed by magnesium and steel half-cells. Use section 24 of the data booklet and assume steel has the standard electrode potential of iron.
8c. [2 marks]
Calculate the free energy change, ΔG⦵, in kJ, of the cell reaction. Use sections 1 and 2 of the data booklet.
8d. [1 mark]
This cell causes the electrolytic reduction of water on the steel. State the half-equation for this reduction.
9a. [3 marks]
Oxidation and reduction reactions can have a variety of commercial uses.
A student decides to build a voltaic cell consisting of an aluminium electrode, Al (s), a tin electrode, Sn (s), and solutions of aluminium nitrate, Al(NO3)3 (aq) and tin(II) nitrate, Sn(NO3)2 (aq).
Electron flow is represented on the diagram.
Label each line in the diagram using section 25 of the data booklet.
9b. [1 mark]
Write the equation for the expected overall chemical reaction in (a).
9c. [1 mark]
Calculate the cell potential using section 24 of the data booklet.
9d. [2 marks]
Calculate the Gibbs free energy change, ΔG⦵, in kJ, for the cell, using section 1 of the data booklet.
If you need the markscheme, including the examiners' reports for each question, and more exam and teaching materials on this topic, contact me through the contact page