Redox Reaction Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Redox Reaction.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

A chemical reaction in which electrons are transferred from one substance (the reducing agent, which is oxidized) to another (the oxidizing agent, which is reduced).

One thing loses electrons (oxidized), another gains them (reduced).

Read the full concept explanation →

How to Use These Examples

Read the first worked example with the solution open so the structure is clear.
Try the practice problems before revealing each solution.
Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Redox Reaction starts by assigning oxidation and reduction, then traces electrons through the wire and ions through solution.

Common stuck point: Students often know a formula related to redox reaction but skip the recognition step: Am I tracking oxidation, reduction, electron flow, ions, electrodes, and whether the cell is spontaneous or driven? That leads to a correct-looking substitution attached to the wrong chemical model.

Sense of Study hint: Ask: Am I tracking oxidation, reduction, electron flow, ions, electrodes, and whether the cell is spontaneous or driven?

Worked Examples

Example 1

easy

Define a redox reaction and explain the relationship between oxidation and reduction.

Answer

\text{Redox: electron transfer. Oxidation = loss, Reduction = gain.}

First step

A redox (reduction-oxidation) reaction involves the transfer of electrons between species.

Full solution

2
Oxidation is the loss of electrons (increase in oxidation number). Reduction is the gain of electrons (decrease in oxidation number).
3
Oxidation and reduction always occur together — one species cannot lose electrons unless another gains them. Remember: OIL RIG (Oxidation Is Loss, Reduction Is Gain).

Redox reactions are one of the most important classes of chemical reactions. They include combustion, corrosion, photosynthesis, respiration, and all electrochemical processes (batteries, electrolysis).

Example 2

medium

In the reaction

\text{Zn(s)} + \text{CuSO}_4\text{(aq)} \rightarrow \text{ZnSO}_4\text{(aq)} + \text{Cu(s)}

, identify the oxidizing agent and the reducing agent.

Example 3

medium

Determine if

\text{AgNO}_3 + \text{NaCl} \rightarrow \text{AgCl} + \text{NaNO}_3

is a redox reaction.

Example 4

medium

In a galvanic cell with Zn(s)/Zn

^{2+}

and Ag

^+

/Ag(s), write the overall balanced redox equation.

Example 5

medium

Balance in acidic solution:

\text{Cr}_2\text{O}_7^{2-} + \text{Fe}^{2+} \rightarrow \text{Cr}^{3+} + \text{Fe}^{3+}

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

medium

Determine whether the following reaction is a redox reaction:

\text{HCl(aq)} + \text{NaOH(aq)} \rightarrow \text{NaCl(aq)} + \text{H}_2\text{O(l)}

. Justify your answer.

Example 2

hard

Balance the following redox reaction in acidic solution using the half-reaction method:

\text{MnO}_4^- + \text{Fe}^{2+} \rightarrow \text{Mn}^{2+} + \text{Fe}^{3+}

Example 3

easy

In the reaction

Zn + Cu^{2+} \rightarrow Zn^{2+} + Cu

, which species is oxidized?

Example 4

easy

What is the oxidation number of oxygen in most compounds such as

H_2O

Example 5

easy

2H_2 + O_2 \rightarrow 2H_2O

, is this a redox reaction?

Example 6

easy

Define a reducing agent.

Example 7

easy

Cu^{2+} + 2e^- \rightarrow Cu

, is copper oxidized or reduced?

Example 8

easy

What is the oxidation number of a free element such as

Na

metal?

Example 9

easy

In a redox reaction, the oxidizing agent is the species that does what to electrons?

Example 10

easy

Find the oxidation number of

S

SO_4^{2-}

Example 11

medium

Balance the oxidation half-reaction for iron going from

Fe^{2+}

Fe^{3+}

Example 12

medium

How many electrons are transferred when

Al \rightarrow Al^{3+}

is balanced with

Cl_2 \rightarrow 2Cl^-

to form

AlCl_3

Example 13

medium

MnO_4^- \rightarrow Mn^{2+}

, what is the change in oxidation number of Mn?

Example 14

medium

Identify the oxidizing agent in

Zn + 2HCl \rightarrow ZnCl_2 + H_2

Example 15

medium

Balance the reduction half-reaction

O_2 \rightarrow O^{2-}

for the oxide ion.

Example 16

medium

2Fe^{3+} + Sn^{2+} \rightarrow 2Fe^{2+} + Sn^{4+}

, how many electrons does tin lose?

Example 17

medium

Is the disproportionation

Cl_2 \rightarrow Cl^- + ClO^-

a redox reaction?

Example 18

medium

What is the oxidation number of nitrogen in

HNO_3

Example 19

medium

Assign the oxidation number of carbon in

CH_4

(methane).

Example 20

challenge

Balance the redox equation in acidic solution:

MnO_4^- + Fe^{2+} \rightarrow Mn^{2+} + Fe^{3+}

Example 21

challenge

A galvanic cell uses

Zn|Zn^{2+}

and

Cu^{2+}|Cu

. Write the balanced overall redox and name the species reduced.

Example 22

challenge

3Cu + 8HNO_3 \rightarrow 3Cu(NO_3)_2 + 2NO + 4H_2O

, how many electrons are transferred total?

Example 23

easy

2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}

, which element is oxidized?

Example 24

easy

What is the oxidation number of H in HCl?

Example 25

easy

2\text{Na} + \text{Cl}_2 \rightarrow 2\text{NaCl}

, which species is the reducing agent?

Example 26

easy

\text{Cl}_2 + 2e^- \rightarrow 2\text{Cl}^-

, is chlorine oxidized or reduced?

Example 27

medium

Find the oxidation number of Cr in

\text{Cr}_2\text{O}_7^{2-}

Example 28

medium

\text{Sn}^{2+} \rightarrow \text{Sn}^{4+} + 2e^-

, is this oxidation or reduction?

Example 29

medium

\text{CuO} + \text{H}_2 \rightarrow \text{Cu} + \text{H}_2\text{O}

, what is the reducing agent?

Example 30

medium

Find the oxidation number of N in

\text{NH}_4^+

Example 31

medium

\text{Cu} + 2\text{Ag}^+ \rightarrow \text{Cu}^{2+} + 2\text{Ag}

, how many electrons are transferred per Cu atom?

Example 32

medium

In the combustion of methane

\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}

, what is the oxidation state change of carbon?

Example 33

medium

At which electrode does oxidation occur in a galvanic cell?

Example 34

medium

\text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2

a redox reaction?

Example 35

medium

Find the oxidation state of Mn in

\text{KMnO}_4

Example 36

hard

Balance in basic solution:

\text{MnO}_4^- + \text{I}^- \rightarrow \text{MnO}_2 + \text{I}_2

Example 37

hard

In the disproportionation

2\text{H}_2\text{O}_2 \rightarrow 2\text{H}_2\text{O} + \text{O}_2

, what oxidation states does O take on each side?

Example 38

hard

How many moles of electrons are transferred when

1

mol Al is oxidized to Al

^{3+}

Example 39

hard

\text{NaH}

, what is the oxidation state of hydrogen?

Example 40

hard

3\text{NO}_2 + \text{H}_2\text{O} \rightarrow 2\text{HNO}_3 + \text{NO}

, identify N's oxidation states and label the disproportionation.

Example 41

hard

In a galvanic cell with overall reaction

\text{Zn} + \text{Cu}^{2+} \rightarrow \text{Zn}^{2+} + \text{Cu}

, identify the species reduced and the cathode material.

Example 42

challenge

For

5\text{H}_2\text{O}_2 + 2\text{MnO}_4^- + 6\text{H}^+ \rightarrow 2\text{Mn}^{2+} + 5\text{O}_2 + 8\text{H}_2\text{O}

, how many electrons are transferred per formula unit of MnO

_4^-

reduced?

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Related Concepts

Oxidation Reduction Electrochemistry Electrochemical Cell

Background Knowledge

These ideas may be useful before you work through the harder examples.

oxidationreduction