Oxidation-Reduction Reactions

Oxidation-Reduction Reactions

​What is Oxidation-Reduction?

​A chemical reaction in which electrons are transferred from one atom or ion to another is called an oxidation-reduction reaction, commonly known as a redox reaction.

A common oxidation reaction occurs when iron metal loses electrons to oxygen. Metals are painted to stop this corrosive reaction.

​Oxidation

​Oxidation is the loss of electrons by the atoms or ions of a substance. The element that loses the electrons is oxidized and becomes more positively charged; that is, its oxidation number increases.

→ [Zn]²⁺ + 2e^- (loss of electrons)

​Reduction

​Reduction is the gain of electrons by the atoms or ions of a substance. The element that acquires the electrons becomes more negatively charged.

+ 2e^- → (gain of electrons)

​Combining Half-Reactions

​The balanced overall equation for the reaction can be written as shown below.

2Zn⁰ + O₂⁰ → 2Zn²⁺ + 2O^2-

​Each atom of zinc atom donates two electrons to each oxygen atom.

Each zinc atom loses electrons and is oxidized.

Each oxygen atom gains and is therefore reduced.

Multiple Choice

Identify which reactant is oxidized and which is reduced in the following reaction.

2Al_(s) + 3Cu²⁺_(aq) →2Al³⁺_(aq) + 3Cu_(s)

• Al is oxidized and Cu²⁺ is reduced.

• Cu²⁺ is oxidized and Al is reduced.

• Both Al and Cu²⁺ are oxidized.

• Both Al and Cu²⁺ are reduced.

Multiple Choice

Identify which reactant is oxidized and which is reduced in the following reaction.

2Cr³⁺_(aq) + 3Zn_(s) →2Cr_(s) + Zn²⁺_(aq)

• Cr³⁺ is oxidized and Zn is reduced.

• Cr³⁺ is reduced and Zn is oxidized.

• Both Cr³⁺ and Zn are oxidized.

• Both Cr³⁺ and Zn are reduced.

Multiple Choice

Identify which reactant is oxidized and which is reduced in the following reaction.

2Au³⁺_(aq) + 3Cd_(s) →2Au_(s) + 3Cd²⁺_(aq)

• Au³⁺ is oxidized and Cd is reduced.

• Au³⁺ is reduced and Cd is oxidized

• Both Au³⁺ and Cd are reduced.

• Both Au³⁺ and Cd are oxidzed.

​Identifying a Redox Reaction

​Redox reactions always involve the the exchange of electrons and many of them involve ionic compounds. Oxygen is not required for an oxidation-reduction reaction.

2Na_(s) + Cl_2(g) → 2NaCl_(s)

​Identifying a Redox Reaction

​An oxidation-reduction does not require oxygen to be present. Oxidation-reduction reaction involve the exchange of electrons and involve ionic compounds.

​Oxidizing and Reducing Agents

• ​ An oxidizing agent is the substance that gains electrons in a redox reaction.

• A reducing agent is the substance that loses electrons in a redox reaction.

Multiple Choice

In which direction do electrons move during a redox reaction?

• from oxidizing agent to the reducing agent

• from the reducing agent to the oxidizing agent

Multiple Choice

What is the oxidizing agent when iron rusts? The oxidizing agent gains electrons.

2Fe_(s) + O_2(g) →FeO_(s)

_{0 0 +2 -2}

• Fe is the oxidizing agent

• O is the oxidizing agent

Multiple Choice

What is the reducing agent when iron rusts? The reducing agent loses electrons.

2Fe_(s) + O_2(g) →FeO_(s)

_{0 0 +2 -2}

• Fe is the reducing agent.

• O is the reducing agent.

Multiple Choice

Which change indicates oxidation?

• Cu becomes Cu²⁺

• Sn⁴⁺ becomes Sn²⁺

• Fe²⁺ becomes Fe

Multiple Choice

Which change indicates oxidation?

• Sn⁴⁺ becomes Sn²⁺

• Cr³⁺ becomes Cr⁶⁺

• Fe³⁺ becomes Fe

Multiple Choice

Which change indicates reduction?

• Cu becomes Cu²⁺

• Sn⁴⁺ becomes Sn²⁺

• Ag becomes Ag⁺

Multiple Choice

Which change indicates reduction?

• Fe becomes Fe²⁺

• Fe²⁺ becomes Fe

• Ag becomes Ag⁺

Multiple Choice

Identify the following reaction as an oxidation reaction or a reduction reaction.

Fe²⁺ → Fe³⁺ + e^-

• Oxidation Reaction

• Reduction Reaction

• Neither a Reduction or an Oxidation Reaction

Multiple Choice

Identify the following reaction as an oxidation reaction or a reduction reaction.

Fe³⁺ + e^- → Fe²⁺

• Oxidation Reaction

• Reduction Reaction

• Neither an Oxidation Reaction or a Reduction Reaction