4.2.3 Oxidation-Reduction Reactions

Question 1

Oxidation-Reduction Reactions

Answer 1

• In an oxidation-reduction reaction, electrons are transferred between a pair of reacting species.
• An oxidation-reduction reaction involves two half-reactions.
• Oxygen is a powerful oxidizing agent(oxidant) as can be seen in the formation of rust during which iron loses electrons to oxygen.

Question 2

oxidation-reduction

Answer 2

• In an oxidation-reduction reaction, electrons are transferred between a pair of reacting species.
• The oxidizing agent (oxidant), in this case the silver ion, gains electrons. The reducing agent(reductant), in this case copper, donates electrons.
• Oxidation involves a loss of electrons and reduction involves a gain of electrons.
• An oxidation-reduction reaction involves two half-reactions.
• Magnesium metal reacts, in an oxidation-reduction reaction, with hydrochloric acid to produce hydrogen gas. In the first half-reaction, oxidation involves the loss of two electrons from the magnesium atom. In the second half-reaction, reduction involves the gain of an electron each by two hydrogen ions.
• The two half-reactions can be combined, by summing, to produce the full reaction. The transferred electrons cancel on either side.
• The oxidation reaction gets its name from oxygen, which is a powerful oxidizing agent (oxidant).
• A common oxidation-reduction reaction is the rusting of iron. In this reaction, iron undergoes oxidation involving a loss of electrons and oxygen undergoes reduction involving a gain of electrons.
• Iron(III) oxide (rust) forms in a later reaction with water.

Question 3

A piece of aluminum metal is dropped into a solution of hydrochloric acid (HCl). Which of these equations best represents the oxidation-reduction reaction that will take place?

Answer 3

2Al(s) + 6H + (aq) + 6Cl − (aq) → 2Al 3+ (aq) + 6Cl − (aq) + 3H2 (g)

Question 4

What is the oxidizing agent in the following reaction?

Cl2(g) + 2Na+ (aq) + 2Br− (aq) → 2Na+ (aq) + 2Cl − (aq) + Br2(l)

Answer 4

Cl2(g)

Question 5

What is the oxidation half-reaction of the following redox reaction?

2Fe(s) + 6H + (aq) + 6Cl − (aq) → 2Fe3+ (aq) + 6Cl − (aq) + 3H2(g)

Answer 5

2Fe (s) → 2Fe3+ (aq) + 6e−

Question 6

When you place a sample of an unknown metal in a solution of Cu(NO3 )2, the metal becomes coated with a layer of copper. When you place a sample of the metal in a solution of HCl, bubbles of hydrogen gas are formed. What can you conclude about the unknown metal based on this information?

Answer 6

It reduces both Cu2+ and H +.

Question 7

What is the reducing agent in the following reaction?

Zn (s) + 2H + (aq) + SO42− (aq) → Zn2+ (aq) + SO42− (aq) + H2 (g)

Answer 7

Zn (s)

Question 8

What is the total number of electrons transferred in the following oxidation-reduction reaction?
2Al(s) + 3Cu2+ (aq) + 6Cl − (aq) →
2Al 3+ (aq) + 6Cl − (aq) + 3Cu (s)

Answer 8

6

Question 9

Which of the following shows a correctly balanced reaction in which cerium is reduced?

Answer 9

Ce4+ (aq) + Fe2+ (aq) →

Ce3+ (aq) + Fe3+ (aq)

Question 10

What is the reduction half-reaction of the following equation?

2K(s) + 2H2O(l) -> 2K+(aq) + 2OH-(aq) + H2(g)

Answer 10

2H2O(l) + 2e- -> 2OH-(aq) + H2(g)

Question 11

Suppose a 5.64 g strip of aluminum metal is placed in a solution of Pb(NO3 )2. What is the maximum mass of lead (Pb) that will precipitate out of the solution as a result of the redox reaction that takes place between Al and Pb(NO3 )2? (Assume that there is an excess of Pb(NO3 )2 in the solution. The unbalanced redox reaction is shown below.)

Al (s) + Pb2+ (aq) + NO3− (aq) → Al 3+ (aq) + NO3− (aq) + Pb (s)

Answer 11

65.1 g