Oxidation and reduction by electrons

Oxidation without oxygen

1. Properties of iron

2. Oxidation without oxygen?

In Chapter 1,

Fe²⁺ Fe X^{2 +}

changes to

Fe³⁺ Fe X^{3 +}

. No oxygen is gained, yet the book calls it oxidation.

Pick the right answer

Predict: what happened to the iron ion?

A. It lost one electron
B. It gained one electron
C. Nothing: without oxygen it cannot be oxidation

Explanation

Going from

Fe²⁺ Fe X^{2 +}

Fe³⁺ Fe X^{3 +}

, the ion loses one electron. Oxidation is loss of electrons, so this is oxidation even without oxygen.

3. Oxidation: loss of electrons

Remember: you met oxidation as gain of oxygen. Here is a wider meaning.

Oxidation

A process in which an atom or ion loses electrons, so its oxidation state increases.

Fe²⁺ \to Fe³⁺ + e- Fe X^{2 +} Fe X^{3 +} + e X^{-}

Loses one electron: +2 → +3

Gaining oxygen is one case of this. In MgO, Mg has lost two electrons to oxygen: 0 → +2.

4. Reduction: gain of electrons

Reduction

A process in which an atom or ion gains electrons, so its oxidation state decreases.

Cu²⁺ + 2e- \to Cu Cu X^{2 +} + 2 e X^{-} Cu

Gains two electrons: +2 → 0

The two happen together. Electrons lost by one substance are gained by another.

5. Worked: zinc in copper sulphate

gatheredZn + CuSO4 →\\ ZnSO4 + Cugathered

Step 1: Oxidation states

Zn: 0 → +2. Cu: +2 → 0. The

SO4 SO X_{4}

group stays −2.

Step 2: Who lost, who gained?

Zn lost 2 electrons: it is oxidized.

Cu²⁺ Cu X^{2 +}

gained 2 electrons: it is reduced.

Step 3: The agents

Zn is the reducing agent: it is itself oxidized.

CuSO4 CuSO X_{4}

is the oxidizing agent: it is itself reduced.

6. Your turn

Sort into groups

Sort each change.

$Na \to Na+ + e- Na Na X^{+} + e X^{-}$ $Cl2 + 2e- \to 2Cl- Cl X_{2} + 2 e X^{-} 2 Cl X^{-}$ $Sn²⁺ \to Sn⁴⁺ + 2e- Sn X^{2 +} Sn X^{4 +} + 2 e X^{-}$ $Fe³⁺ + e- \to Fe²⁺ Fe X^{3 +} + e X^{-} Fe X^{2 +}$

Pick the right answer

2Na + Cl2 \to 2NaCl 2 Na + Cl X_{2} 2 NaCl

, which is the oxidizing agent?

A. $Cl2 Cl X_{2}$
B. Na
C. None: no oxygen is involved
D. NaCl

Explanation

Na: 0 → +1 (oxidized, reducing agent). Cl: 0 → −1 (reduced, oxidizing agent).

7. Summary

Oxidation: loss of electrons; the oxidation state increases.
Reduction: gain of electrons; the oxidation state decreases.
The oxidizing agent gains electrons (it is reduced). The reducing agent loses electrons (it is oxidized).

Back to the hook:

Fe²⁺ \to Fe³⁺ + e- Fe X^{2 +} Fe X^{3 +} + e X^{-}

is oxidation. Next lesson: why it happens so easily.

Can you explain why

Cl2 Cl X_{2}

is an oxidizing agent, though no oxygen is involved?

Reveal

2Na + Cl2 \to 2NaCl 2 Na + Cl X_{2} 2 NaCl

, chlorine gains electrons (0 → −1), so it is reduced. The substance that gains electrons is the oxidizing agent, with or without oxygen.

Concepts in this lesson