PART B: WRITTEN-RESPONSE QUESTIONS

For questions involving calculation, full marks will NOT be given for

providing only an answer.

1. Written below is a skeleton oxidation-reduction reaction:

MnO4- + SeO —> Mn2O3 + SeO32-

Assign oxidation numbers to Mn and Se in each species. Identify the oxidizing agent and state why

you chose it. (4 marks)

Oxidation Number:

of Mn in MnO4- = __________

of Se in SeO = __________

of Mn in Mn2O3 = __________

of Se in SeO32- = __________

Oxidizing agent: _____________________________________________________________

Reason: ____________________________________________________________________

2. Balance the following redox reaction occurring in an acidic solution. (4 marks)

As + ClO3- —> H3AsO3 + HClO

3. Balance the equation for the following redox reaction taking place in a basic solution: (4 marks)

MnO4- + C2O42- —> CO32- + MnO2

4. The data below were obtained in a redox titration of a 25.00 mL sample containing Sn2+ ions

using 0.125 M KMnO4 according to the following reaction:

2MnO4- + 16H+ + 5Sn2+ —> 2Mn2+ + 8H2O + 5Sn4+

Calculate the [Sn2+] in the original sample. (4 marks)

Use the following diagram of a cell at 25 °C to answer question 5.

5. The electrochemical cell above produces an initial voltage of 0.93 volts.

(a) Identify the metal "X". (1 mark)

(b) Identify a suitable electrolyte "Y". (1 mark)

(c) Identify a suitable electrolyte "Z". (1 mark)

(d) Indicate, on the diagram, the direction of electron flow. (1 mark)

6. Cathodic protection is one method used to inhibit the corrosion of iron.

(a) Explain the principle of cathodic protection. (2 marks)

(b) Identify two methods, other than cathodic protection, that could be used to

inhibit the corrosion of iron. (2 marks)

7. Consider the following diagram:

Students are asked to produce hydrogen and oxygen gas by the electrolysis of

water. They are given three substances (CuSO4, K2SO4 and NaI) to choose from

to prepare an electrolytic solution that will only produce hydrogen and oxygen.

(a) Which substance should be selected? Explain why. (3 marks)

Substance:

Explanation:

(b) Write the equation for the half–reaction that occurs at the anode in the

electrolytic cell. (1 mark)

(c) Explain why it would not be acceptable to use a copper anode in this cell. (1 mark)

8. a) Sketch and label an electrolytic cell which could be used to plate a strip of Fe with Ni.

Identify the positive and negative terminals and the materials used for the anode and the

electrolyte. (2 marks)

b) Write the cathode half-reaction. (1 mark)