Oxidation Examples in Chemistry

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

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

Concept Recap

The loss of electrons by an atom, ion, or molecule during a chemical reaction, resulting in an increase in its oxidation state.

Giving away electrons. Originally meant 'gaining oxygen' but it's broader.

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: Oxidation 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 oxidation 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
In the reaction 2Mg+O2→2MgO2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}, identify which species is oxidized.

Answer

Mg is oxidized (0 → +2)\text{Mg is oxidized (0 → +2)}

First step

1
Mg goes from oxidation state 00 (element) to +2+2 (in MgO).

Full solution

  1. 2
    An increase in oxidation number means the species has lost electrons.
  2. 3
    Therefore, Mg is oxidized: Mg→Mg2++2e−\text{Mg} \rightarrow \text{Mg}^{2+} + 2e^-.
Oxidation is the loss of electrons (OIL RIG: Oxidation Is Loss). The substance that is oxidized serves as the reducing agent because it provides electrons to the other reactant.

Example 2

medium
In the reaction Zn+Cu2+→Zn2++Cu\text{Zn} + \text{Cu}^{2+} \rightarrow \text{Zn}^{2+} + \text{Cu}, write the oxidation and reduction half-reactions.

Example 3

medium
In Fe+CuSO4→FeSO4+Cu\text{Fe} + \text{CuSO}_4 \rightarrow \text{FeSO}_4 + \text{Cu}, write the oxidation half-reaction.

Example 4

medium
Show how a galvanic cell with Zn anode and Cu cathode uses oxidation.

Example 5

hard
Balance the oxidation of I−\text{I}^- to IO3−\text{IO}_3^- in acidic solution.

Practice Problems

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

Example 1

easy
Is iron rusting an example of oxidation? Explain.

Example 2

medium
In the reaction CuO+H2→Cu+H2O\text{CuO} + \text{H}_2 \rightarrow \text{Cu} + \text{H}_2\text{O}, which substance is oxidized?

Example 3

easy
Define oxidation in terms of electrons.

Example 4

easy
Does oxidation increase or decrease the oxidation state of a species?

Example 5

easy
In Zn→Zn2++2e−\text{Zn}\rightarrow\text{Zn}^{2+}+2e^-, is zinc oxidized or reduced?

Example 6

easy
Is oxidation always accompanied by reduction in a chemical reaction?

Example 7

easy
The species that gets oxidized acts as the oxidizing agent or the reducing agent?

Example 8

easy
What is the oxidation state of an element in its pure form, like Fe\text{Fe} metal?

Example 9

easy
Originally 'oxidation' meant gaining oxygen. Is the modern definition broader or narrower?

Example 10

easy
When magnesium burns to form MgO\text{MgO}, Mg goes from 0 to +2+2. Is it oxidized?

Example 11

medium
In 2Na+Cl2→2NaCl2\text{Na}+\text{Cl}_2\rightarrow2\text{NaCl}, identify which element is oxidized.

Example 12

medium
In Zn+Cu2+→Zn2++Cu\text{Zn}+\text{Cu}^{2+}\rightarrow\text{Zn}^{2+}+\text{Cu}, which species is oxidized and is it the reducing agent?

Example 13

medium
Write the oxidation half-reaction for iron forming Fe3+\text{Fe}^{3+}.

Example 14

medium
Carbon in CH4\text{CH}_4 (−4-4) becomes CO2\text{CO}_2 (+4+4). How many electrons does each carbon lose?

Example 15

medium
Why is burning hydrogen (2H2+O2→2H2O2\text{H}_2+\text{O}_2\rightarrow2\text{H}_2\text{O}) an oxidation of hydrogen?

Example 16

medium
In 2Mg+O2→2MgO2\text{Mg}+\text{O}_2\rightarrow2\text{MgO}, write Mg's oxidation half-reaction.

Example 17

medium
In Cl2+2Br−→2Cl−+Br2\text{Cl}_2+2\text{Br}^-\rightarrow2\text{Cl}^-+\text{Br}_2, which species is oxidized?

Example 18

medium
In Fe2+→Fe3++e−\text{Fe}^{2+}\rightarrow\text{Fe}^{3+}+e^-, is iron oxidized, and how many electrons are lost?

Example 19

medium
In 2Al+3Cl2→2AlCl32\text{Al}+3\text{Cl}_2\rightarrow2\text{AlCl}_3, which element is oxidized and what is its oxidation-state change?

Example 20

challenge
In MnO4−→Mn2+\text{MnO}_4^-\rightarrow\text{Mn}^{2+}, Mn changes oxidation state. Determine whether Mn is oxidized or reduced and the electrons involved.

Example 21

challenge
Balance the electrons: Al→Al3++3e−\text{Al}\rightarrow\text{Al}^{3+}+3e^- and Cu2++2e−→Cu\text{Cu}^{2+}+2e^-\rightarrow\text{Cu} are combined. Find the whole-number coefficients.

Example 22

challenge
In the combustion C+O2→CO2\text{C}+\text{O}_2\rightarrow\text{CO}_2, identify the oxidized element, the reduced element, and the oxidizing agent.

Example 23

easy
When Mg\text{Mg} becomes Mg2+\text{Mg}^{2+}, how many electrons does each magnesium atom lose?

Example 24

easy
Iron rusting: 4Fe+3O2→2Fe2O34\text{Fe} + 3\text{O}_2 \rightarrow 2\text{Fe}_2\text{O}_3. What is iron's change in oxidation number?

Example 25

easy
True or false: oxidation must always involve oxygen gas.

Example 26

easy
Write the oxidation half-reaction for K\text{K} becoming K+\text{K}^+.

Example 27

easy
Ca→Ca2++2e−\text{Ca} \rightarrow \text{Ca}^{2+} + 2e^-. Is this oxidation or reduction?

Example 28

medium
In Sn+2HCl→SnCl2+H2\text{Sn} + 2\text{HCl} \rightarrow \text{SnCl}_2 + \text{H}_2, identify the oxidized species.

Example 29

medium
In CH4+2O2→CO2+2H2O\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}, identify the element that is oxidized.

Example 30

medium
Cu→Cu2++2e−\text{Cu} \rightarrow \text{Cu}^{2+} + 2e^- has E∘=−0.34E^\circ = -0.34 V. What does the negative value mean for spontaneity as written?

Example 31

medium
Write the oxidation half-reaction for sulfide ion forming elemental sulfur.

Example 32

medium
In 2H2S+O2→2S+2H2O2\text{H}_2\text{S} + \text{O}_2 \rightarrow 2\text{S} + 2\text{H}_2\text{O}, which atoms are oxidized?

Example 33

medium
In ethanol combustion C2H5OH+3O2→2CO2+3H2O\text{C}_2\text{H}_5\text{OH} + 3\text{O}_2 \rightarrow 2\text{CO}_2 + 3\text{H}_2\text{O}, is carbon oxidized? Justify with oxidation numbers.

Example 34

medium
Which is the stronger reducing agent under standard conditions, Zn or Cu? Why?

Example 35

medium
In 2Ag++Cu→2Ag+Cu2+2\text{Ag}^+ + \text{Cu} \rightarrow 2\text{Ag} + \text{Cu}^{2+}, write the oxidation half-reaction and the number of electrons transferred per formula unit.

Example 36

medium
Is the bleaching of a stain by hydrogen peroxide a kind of oxidation?

Example 37

medium
In Sn2+→Sn4++2e−\text{Sn}^{2+} \rightarrow \text{Sn}^{4+} + 2e^-, identify oxidation and the change in oxidation number.

Example 38

hard
Balance the oxidation half-reaction Mn2+→MnO4−\text{Mn}^{2+} \rightarrow \text{MnO}_4^- in acidic solution.

Example 39

hard
In 5C2O42−+2MnO4−+16H+→10CO2+2Mn2++8H2O5\text{C}_2\text{O}_4^{2-} + 2\text{MnO}_4^- + 16\text{H}^+ \rightarrow 10\text{CO}_2 + 2\text{Mn}^{2+} + 8\text{H}_2\text{O}, identify the species oxidized and the electrons lost per oxalate.

Example 40

hard
Combine Al→Al3++3e−\text{Al} \rightarrow \text{Al}^{3+} + 3e^- with Fe3++3e−→Fe\text{Fe}^{3+} + 3e^- \rightarrow \text{Fe} to balance the redox.

Example 41

hard
Combine Mg→Mg2++2e−\text{Mg} \rightarrow \text{Mg}^{2+} + 2e^- and Al3++3e−→Al\text{Al}^{3+} + 3e^- \rightarrow \text{Al} into a balanced overall equation.

Example 42

challenge
Balance the oxidation of ethanol to acetic acid in acidic solution: C2H5OH→CH3COOH\text{C}_2\text{H}_5\text{OH} \rightarrow \text{CH}_3\text{COOH}.
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Background Knowledge

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

electronion