IBDP Official Exam Material
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Unit 2: Energetics, Group Chemistry, Halogenoalkanes and Alcohols
Topic 9: Redox processes
For both SL and HL students
1. [1 mark]
What occurs during the operation of a voltaic cell based on the given reaction?
2Cr (s) + 3Fe2+ (aq) → 2Cr3+ (aq) + 3Fe (s)
2. [1 mark]
Which substance is the reducing agent in the given reaction?
H+ (aq) + 2H2O (l) + 2MnO4− (aq) + 5SO2 (g) → 2Mn2+ (aq) + 5HSO4− (aq)
A. H+
B. H2O
C. MnO4−
D. SO2
3. [1 mark]
Which combination is correct regarding the anode and electron flow in an electrolytic cell?
4a. [2 marks]
The diagram shows an unlabelled voltaic cell for the reaction:
Cu2+ (aq) + Fe (s) → Fe2+ (aq) + Cu (s)
Label the diagram with the species from the equation and the direction of electron flow.
4b. [1 mark]
Write the half-equation for the reaction occurring at the anode (negative electrode).
4c. [1 mark]
The diagram includes a salt bridge that is filled with a saturated solution of KNO3. Outline the function of the salt bridge.
4d. [2 marks]
Predict the movement of all ionic species through the salt bridge.
5. [1 mark]
In which of the following species would sulfur be reduced if converted to SCl2?
A. S2O32–
B. H2S
C. S
D. SO2
6. [1 mark]
Which statement is correct for both voltaic and electrolytic cells?
A. The oxidation reaction releases electrons.
B. The oxidation reaction occurs at the positive electrode.
C. The cathode is negative.
D. Electrons flow through the electrolyte.
7. [1 mark]
How many electrons are needed when the following half-equation is balanced using the lowest possible whole numbers?
__ NO3– (aq) + __ H+ (aq) + __ e– → __ NO (g) + __ H2O (l)
A. 1
B. 2
C. 3
D. 5
8. [1 mark]
What is the name of the compound with formula Ti3(PO4)2?
A. Titanium phosphate
B. Titanium(II) phosphate
C. Titanium(III) phosphate
D. Titanium(IV) phosphate
9. [1 mark]
Which species could be reduced to form NO2?
A. N2
B. NO3−
C. HNO2
D. NO
10. [1 mark]
Which combination best describes what is happening to chloromethane, CH3Cl, in the equation below?
CH3Cl (g) + H2 (g) ⇌ CH4 (g) + HCl (g)
A. Oxidation and addition
B. Oxidation and substitution
C. Reduction and addition
D. Reduction and substitution
11. [1 mark]
The arrows represent electron flow in the diagram. What does terminal X on the battery represent?
A. Anode and positive terminal
B. Anode and negative terminal
C. Cathode and positive terminal
D. Cathode and negative terminal
12. [2 marks]
Molten zinc chloride undergoes electrolysis in an electrolytic cell at 450 °C.
Deduce the half-equations for the reaction at each electrode.
Deduce the half-equations for the reaction at each electrode.
15b. [2 marks]
Deduce the overall cell reaction including state symbols. Use section 7 of the data booklet.
16. [1 mark]
What is the change in the oxidation state of oxygen?
2Fe2+ (aq) + H2O2 (aq) + 2H+ (aq) → 2H2O (l) + 2Fe3+ (aq)
A. +1
B. 0
C. −1
D. −2
17. [1 mark]
Which statement is correct about the electrolysis of molten lead(II) bromide, PbBr2?
A. Br− ions accept electrons at the cathode (negative electrode).
B. Pb2+ ions accept electrons at the anode (positive electrode).
C. Br− ions lose electrons at the anode (positive electrode).
D. Pb2+ ions lose electrons at the cathode (negative electrode).
18. [1 mark]
Consider this voltaic cell, where Cu is a more reactive metal than Ag:
19a. [1 mark]
Biochemical oxygen demand (BOD) can be determined by the Winkler Method.
Outline what is measured by BOD.
19b. [2 marks]
A student dissolved 0.1240 ± 0.0001 g of Na2S2O3 to make 1000.0 ± 0.4 cm3 of solution to use in the Winkler Method.
Determine the percentage uncertainty in the molar concentration.
19c. [1 mark]
A 25.00 cm3 sample of water was treated according to the Winkler Method.
Step I: 2Mn2+ (aq) + O2 (g) + 4OH− (aq) → 2MnO2 (s) + 2H2O (l)
Step II: MnO2 (s) + 2I− (aq) + 4H+ (aq) → Mn2+ (aq) + I2 (aq) + 2H2O (l)
Step III: 2S2O32− (aq) + I2 (aq) → 2I− (aq) + S4O62− (aq)
The iodine produced was titrated with 37.50 cm3 of 5.000 × 10−4 mol dm−3 Na2S2O3.
Calculate the amount, in moles of Na2S2O3 used in the titration.
19d. [1 mark]
Deduce the mole ratio of O2 consumed in step I to S2O32− used in step III.
19e. [2 marks]
Calculate the concentration of dissolved oxygen, in mol dm−3, in the sample.
19f. [1 mark]
The three steps of the Winkler Method are redox reactions.
Deduce the reduction half-equation for step II.
20. [1 mark]
A student performed displacement reactions using metals W and X and solutions of salts of metals W, X, Y and Z. The results are summarized in the table.
Which of the four metals is most reactive?
A. W
B. X
C. Y
D. Z
21. [1 mark]
What is correct for this redox reaction?
MnO2 (s) + 2I− (aq) + 4H+ (aq) → Mn2+ (aq) + I2 (aq) + 2H2O (l)
22. [1 mark]
Which statements are correct for electrolysis?
I. An exothermic reaction occurs.
II. Oxidation occurs at the anode (positive electrode).
III. The reaction is non-spontaneous.
II. Oxidation occurs at the anode (positive electrode).
III. The reaction is non-spontaneous.
A. I and II only
B. I and III only
C. II and III only
D. I, II and III
23. [1 mark]
What is the oxidation state of oxygen in H2O2?
A. −2
B. −1
C. +1
D. +2
24. [1 mark]
What are the products of the electrolysis of molten potassium chloride, KCl (l)?
25. [1 mark]
What are the oxidation states of oxygen?
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