Oxidising and Reducing Agents

1. Write a half equation for each of the changes shown below and state whether they are oxidation or reduction half-equations.

a) Hg  ®  Hg²⁺

b) Cr³⁺ ®  Cr

c) I₂  ®  I^–

d) F^–  ®  F

e) Fe²⁺  ®  Fe³⁺

f) Sn²⁺  ®  Sn⁴⁺

g) Fe₂O₄   -®  Fe³⁺

h) Cl₂  ®  ClO₃^–

i) O₂   ®  H₂O₂

j) I₂ ® IO₃^–

2. In each of the following examples write:

i) the ion-electron half equation for the oxidation and reduction process

ii) the overall REDOX equation for the reaction

iii) the names of the oxidising and reducing agent

a) A displacement reaction between zinc and silver (II) nitrate

b) A reaction where calcium is added to dilute hydrochloric acid  

c) The reaction of acidified potassium permanganate solution with sodium bromide solution

3. Which of the following is a redox reaction?

A          NaOH   +   HCl   ®   NaCl   +   H₂O

B          Zn   +   2HCl       ®   ZnCl₂   +   H₂

C           NiO   +   2HCl     ®   NiCl₂   +   H₂O

D          CuCO₃  +  2HCl  ®   CuCl₂  +  H₂O + CO₂

4. During a redox process in acid solution, iodate ions, IO₃^– _(aq) , are converted into iodine, I_{2 (aq).}

            IO₃^– _(aq)    ®   I_{2 (aq)}

The numbers of H⁺ _(aq) and H₂O_(l) required to balance the ion-electron equation for the formation of 1 mol of I_2(aq) are, respectively

A         6 and 3

B          3 and 6

C          12 and 6

D         6 and 12

5. Iodide ions can be oxidised using acidified potassium permanganate solution. The equations are:

            2I^–_(aq)  ®  I_2(aq)  +  2e^–

            MnO₄^–_(aq)  +  8H⁺(aq)  +  5e^–  ®Mn²⁺_(aq)  +  4H₂O_(l)

How many moles of iodide ions are oxidised by one mole of permanganate ions?

A         1.0

B         2.0

C         2.5

D         5.0

6. Stanic chloride (SnCl₄) was used in World War 1 as a chemical weapon due to its corrosive and toxic properties. It can be produced by the reaction shown.

What ion is oxidized in the above reaction?

7. In which of the following reactions is hydrogen acting as an oxidising agent?

8. During a redox process, chlorate ions are converted into chlorine.

The reaction is carried out in acidic conditions to provide H+ ions. How many H+ ions would be required to balance this ion-electron equation?

A 12

B 10

C 8

D 6

9. The ion electron equations for the oxidation and reduction reactions that take place in a methanol fuel cell are:

Combine the two ion-electron equations to give the equation for the overall redox reaction.

10. Acrylonitrile can be reduced to form CH₃CH₂CN. Complete and balance the ion-electron equation for the reduction reaction.

The ion electron equation for the oxidation of copper by nitric acid are shown

How many moles of copper ions are oxidised by 1 mole of nitrate ions?

A 0.33

B 0.67

C 1.50

D 3.00

11. What is the significance of the acronym ‘OILRIG’ when explaining a redox process.

12.      What is meant by a spectator ion?

13.      For the following displacement reactions write down the relevant ion-electron equations and use them to work out the redox equation.  Do not include the spectator ions.

(a) copper metal reacts with silver(I) nitrate solution to form copper (II) nitrate solution and silver.

(b) chromium metal reacts with nickel (II) sulphate solution to form chromium (III) sulphate solution and nickel.

(c) magnesium metal displaces aluminium from aluminium (III) oxide.

(d) copper is displaced from a solution of copper (II) sulphate by sodium metal.

14.  Give the names of two strong oxidising agents and give two uses of each.

15.   The ion-electron equations below represent the reduction and oxidation reactions which take         place when an acidified solution of dichromate ions react with sulphite ions.

          Cr₂O₇^2-(aq)  +  14H⁺(aq)  +  6e^–                  2Cr³⁺(aq)  +  7H₂O(l)

          SO₃^2-(aq) +  H₂O(l)                SO₄^2-(aq) +  2H⁺(aq) +  2e^–

             Write the REDOX equation for this reaction.

16. Sulphur dioxide is added to wine as a preservative.   A mass of 20 to 40 mg of sulphur dioxide             per litre of wine will safeguard the wine without affecting its taste.

(a) Describe clearly, with full experimental detail, how 0.05 mol l^-1 iodine solution would be diluted to give 250 cm³ of 0.005 mol l^-1 solution.

(b) The equation for the reaction which takes place is:

                                    SO_2(aq)  +  I_2(aq)  +  2H₂O_(l)   ®   4H⁺(aq)  +  SO₄^2-_(aq)  +  2I^–_(aq)

(i) The indicator used in this reaction causes a change from blue to colourless at the end point. Name a substance which could be used as this indicator.

(ii) Write the ion-electron equation for the reduction reaction taking place.