Pupils can confuse oxidation and reduction when involving electrons. They often mistake a positive charge on an ion as meaning electrons have been added and vice versa for negative ions.

It is very important to teach from first principles what causes the charges and then work up to half equations where the pupils can see the electrons in the equations, finally combining these to form ionic equations.

Keywords

Oxidation - A type of reaction in which a substance gains oxygen or loses electrons.
Half equation - A chemical equation used to show the electrons lost in oxidation or the electrons gained in reduction.
Reduction - A type of reaction in which a substance loses oxygen or gains electrons.
Redox - A redox reaction is one in which a substance is oxidised and another is reduced.
Ionic equation - A chemical equation in which reacting ions are shown; unreacting ions (spectator ions) are not included.

Pupils need much practise so many half equation examples of species being both oxidised and reduced helps.

Teacher tip

Equipment

None required.

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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6 Questions

Q1.

Match the keyword to the correct statement.

Correct Answer:displacement ,when an element replaces a less reactive element in a compound

when an element replaces a less reactive element in a compound

Correct Answer:halide,name of the salts formed from halogens

name of the salts formed from halogens

Correct Answer:halogen,non-metallic elements in Group 7 that react with metals to form salt

non-metallic elements in Group 7 that react with metals to form salt

Correct Answer:salts,ionic compounds made of positive and negative ions

ionic compounds made of positive and negative ions

Q2.

What happens when Group 2 elements react with a halogen?

Each Group 2 atom transfers an outer electron to a Group 7 atom.

Each Group 2 atom transfers two outer electrons to a Group 7 atom.

Correct answer: Each Group 2 atom transfers two outer electrons to two separate Group 7 atoms.

Correct answer: Group 2 atoms form positively charged ions.

Group 2 atoms form negatively charged ions.

Q3.

Which is the correct symbol equation for a reaction between magnesium and chlorine?

magnesium + chlorine → magnesium chloride

Mg(s) + Cl (g) → MgCl (s)

Mg(s) + 2Cl(g) →MgCl₂(s)

Correct answer: Mg(s) + Cl₂ (g) → MgCl₂ (s)

Q4.

Which is the correct formula for barium bromide?

BaBr

BBr₂

Ba₂Br₂

Correct answer: BaBr₂

Q5.

Which of the following experiments will result in a displacement reaction?

iodine + potassium bromide

iodine + potassium chloride

bromine + potassium chloride

Correct answer: chlorine + potassium iodide

Q6.

+ F₂ → 2CsF

Correct Answer: 2Cs

Exit quiz

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6 Questions

Q1.

What does a negative charge on an ion mean?

An atom has lost an electron from its outer shell.

Correct answer: An atom has gained an electron.

Correct answer: There are more electrons than protons present in the ion

There are more protons than electrons present in the ion.

Q2.

What type of reaction occurs when a metal atom loses an outer electron to become a positive stable ion?

reduction

neutralisation

decomposition

Correct answer: oxidation

Q3.

Choose the correct half equation.

Correct answer: Na → Na⁺ + e⁻

Na → Na²⁺ + 2e⁺

Na → Na⁻ + e⁺

2Na → 2Na⁻ + e⁺

Q4.

Which one of the following half equations is correct?

Correct answer: Cl₂ + 2e⁻ → 2Cl⁻

Cl₂ + 2e⁻ → Cl₂⁻

Cl₂ + 2e⁻ → Cl₂²⁻

Cl₂ + 2e⁻ → Cl⁻

Q5.

Which half equations show a reduction reaction?

Mg → Mg²⁺ + 2e⁻

Correct answer: Br₂ + 2e⁻ → 2Br⁻

Na → Na⁺ + e⁻

Correct answer: O₂ + 4e⁻ → 2O²⁻

Q6.

Look at this displacement reaction: F₂ (aq) + 2 KI (aq) → I₂ (aq) + 2KF (aq). Identify a spectator ion.

Correct answer: K⁺

F₂

K⁺ I⁻

I⁻