Reactivity of metals study guide

Reactivity of Metals

1. The Reactivity Series

The reactivity series is a list of metals arranged from most to least reactive. It is a practical tool for predicting how a metal will behave in common reactions such as with water, steam, dilute acids and other metal salts.

| Rank | Metal | Typical Reaction | Key Observation | |------|-------|------------------|-----------------| | 1 | Potassium | K + H₂O → KOH + H₂ | vigorous, sparks | | 2 | Sodium | Na + H₂O → NaOH + H₂ | vigorous, flame | | 3 | Lithium | Li + H₂O → LiOH + H₂ | moderate | | 4 | Calcium | Ca + H₂O → Ca(OH)₂ + H₂ | moderate | | 5 | Magnesium | Mg + H₂O (steam) → MgO + H₂ | slow at room temp | | 6 | Carbon | C + H₂O (steam) → CO + H₂ | gas evolution | | 7 | Zinc | Zn + H₂O (steam) → ZnO + H₂ | slow | | 8 | Iron | Fe + H₂O (steam) → FeO + H₂ | slow | | 9 | Hydrogen | H₂ + O₂ → H₂O | combustion | |10 | Copper | Cu + H₂O (steam) → CuO + H₂ | very slow | |11 | Gold | Au + H₂O (steam) → AuO₂ + H₂ | negligible |

> Why the order matters – A metal higher in the series will displace a metal lower in the series from its salt. For example, zinc displaces iron from iron(II) chloride: > > > Word equation: Zinc + iron(II) chloride → iron + zinc(II) chloride > > Symbol equation: Zn + FeCl₂ → Fe + ZnCl₂

1.1 Reactions with Water, Steam and Dilute Acids

| Metal | Water | Steam | Dilute Acid | Observation | |-------|-------|-------|-------------|-------------| | Potassium | reacts violently, sparks | reacts violently | reacts violently | vigorous gas evolution | | Sodium | reacts violently | reacts violently | reacts violently | vigorous gas evolution | | Lithium | reacts slowly | reacts slowly | reacts slowly | gas evolution | | Calcium | reacts slowly | reacts slowly | reacts slowly | gas evolution | | Magnesium | no reaction | reacts slowly | reacts slowly | gas evolution | | Zinc | no reaction | reacts slowly | reacts slowly | gas evolution | | Iron | no reaction | reacts slowly | reacts slowly | gas evolution | | Copper | no reaction | no reaction | no reaction | no gas | | Gold | no reaction | no reaction | no reaction | no gas |

> Rule of thumb – If a metal reacts with water or steam, it is higher in the reactivity series than hydrogen. If it reacts with a dilute acid, it is higher than the metal in the acid’s salt.

2. Metal Oxides

2.1 Basic vs Acidic Oxides

| Oxide | Element | Acidic or Basic | Solubility in Water | |-------|---------|-----------------|---------------------| | Na₂O | Sodium | Basic (alkali) | Soluble | | CaO | Calcium | Basic (alkali) | Soluble | | Al₂O₃ | Aluminium | Amphoteric (acts as base) | Insoluble | | CO₂ | Carbon | Acidic | Soluble | | SO₃ | Sulphur | Acidic | Soluble | | NO₂ | Nitrogen | Acidic | Soluble |

> Key point – Metal oxides that contain a metal are usually basic. Non‑metal oxides are acidic. Some oxides, like Al₂O₃, are amphoteric and can behave as either.

2.2 Dissolution and Neutralisation

When a basic metal oxide dissolves in water it forms an alkaline solution. For example:

Na₂O + H₂O → 2 NaOH

The hydroxide ions (OH⁻) give the solution a high pH. If this solution reacts with an acid, neutralisation occurs, producing water and a salt:

NaOH + HCl → NaCl + H₂O

> Remember – The salt formed contains the cation of the metal and the anion of the acid.

2.3 Insoluble Bases vs Soluble Alkalis

• Soluble alkalis (e.g., NaOH, KOH) dissolve readily in water and give a clear, strongly alkaline solution.
• Insoluble bases (e.g., Al₂O₃) do not dissolve in water and therefore do not produce an alkaline solution.

3. Extraction of Metals

3.1 Unreactive Metals

Metals that are very low in the reactivity series, such as gold, are found in the Earth as the pure metal because they do not react with oxygen or other elements to form compounds.

3.2 Extraction by Reduction

Most metals are found as oxides or silicates and must be extracted by removing the oxygen. Two common methods are:

| Method | Reaction | When Used | |--------|----------|-----------| | Carbon reduction | M₂O₃ + 3C → 2M + 3CO | For metals less reactive than carbon (e.g., iron, aluminium) | | Electrolysis | M⁺ + e⁻ → M | For metals more reactive than carbon (e.g., sodium, potassium) |

> Why carbon works – Carbon is more reactive than metals like iron and aluminium, so it can remove oxygen from their oxides. > > Why electrolysis is needed – Metals such as sodium are more reactive than carbon; carbon cannot remove the oxygen, so an electric current is used to reduce the metal ions.

3.3 Linking Extraction to the Reactivity Series

The position of a metal in the reactivity series determines its extraction method:

• High reactivity (e.g., Na, K) – Extracted by electrolysis because they cannot be reduced by carbon.
• Low reactivity (e.g., Fe, Al) – Extracted by carbon reduction because they are less reactive than carbon.

4. Oxidation and Reduction (High‑Throughput Only)

4.1 Definitions

• Oxidation – Loss of electrons (increase in oxidation state).
• Reduction – Gain of electrons (decrease in oxidation state).

4.2 Electron‑Transfer in Displacement Reactions

In a displacement reaction, a more reactive metal (M₁) gives up electrons to a less reactive metal ion (M₂⁺):

M₁ → M₁⁺ + e⁻ (oxidation)

M₂⁺ + e⁻ → M₂ (reduction)

The net reaction is the same as the word or symbol equation for the displacement.

4.3 Identifying Oxidised and Reduced Species

• The species that loses electrons is oxidised.
• The species that gains electrons is reduced.

> Example – In the reaction Zn + FeCl₂ → Fe + ZnCl₂, zinc is oxidised (Zn → Zn²⁺ + 2e⁻) and iron(II) is reduced (Fe²⁺ + 2e⁻ → Fe).

4.4 Half‑Equations

When ions and charges are supplied, simple ionic half‑equations can be written:

• Oxidation: M → Mⁿ⁺ + ne⁻
• Reduction: Mⁿ⁺ + ne⁻ → M

These half‑equations help visualise electron flow in redox reactions.

4.5 Oxygen‑Transfer vs Electron‑Transfer Explanations

• Oxygen‑transfer – Explains reactions in terms of oxygen moving between species (e.g., metal oxide + carbon → metal + CO).
• Electron‑transfer – Focuses on electrons moving between species (e.g., displacement reactions).

Both approaches describe the same underlying chemistry but emphasise different aspects.

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5. Summary of Key Points

1. Reactivity series – Order of metals predicts reactions with water, steam, acids and displacement reactions.
2. Metal oxides – Metal oxides are basic; non‑metal oxides are acidic. Basic oxides dissolve to give alkaline solutions.
3. Extraction – Metals less reactive than carbon are extracted by carbon reduction; more reactive metals require electrolysis.
4. Redox – Oxidation is loss of electrons; reduction is gain of electrons. Displacement reactions are redox processes.
5. Practical application – Use the reactivity series to determine extraction methods and predict reaction outcomes.

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6. Quick‑Reference Tables

6.1 Reactivity Series (Top 11)

| Rank | Metal | |------|-------| | 1 | Potassium | | 2 | Sodium | | 3 | Lithium | | 4 | Calcium | | 5 | Magnesium | | 6 | Carbon | | 7 | Zinc | | 8 | Iron | | 9 | Hydrogen | |10 | Copper | |11 | Gold |

6.2 Metal Oxide Properties

| Oxide | Acidic / Basic | Soluble in water | |-------|----------------|------------------| | Na₂O | Basic (alkali) | Yes | | CaO | Basic (alkali) | Yes | | Al₂O₃ | Amphoteric | No | | CO₂ | Acidic | Yes | | SO₃ | Acidic | Yes |

6.3 Extraction Methods

| Metal | Extraction Method | Reason | |-------|-------------------|--------| | Na, K | Electrolysis | Cannot be reduced by carbon | | Fe, Al | Carbon reduction | Less reactive than carbon |

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7. Practice Questions (No Calculations)

1. Predict whether the oxide of a given metal will be acidic or basic.
2. Write the balanced symbol equation for a displacement reaction between zinc and copper(II) sulfate.
3. Explain why gold is found in the Earth as the pure metal.
4. Describe the difference between an insoluble base and a soluble alkali.
5. Identify the oxidised and reduced species in the reaction: Fe + CuSO₄ → FeSO₄ + Cu.

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8. Further Reading

• *AQA GCSE Chemistry Revision Guide – Chemical Changes* (chapter on metal reactivity)
• *Chemistry for GCSE – AQA* (sections on redox and extraction)
• *BBC Bitesize – Reactivity series* (interactive quizzes)

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End of Study Guide