# Reactivity Series

> Edexcel International GCSE Chemistry · 4CH1 2017
> Source: https://www.owlsprep.com/study/edexcel-igcse-chemistry-s2-reactivity-series/

This guide covers all Edexcel IGCSE Chemistry (4CH1) reactivity series content, including metal reactions with water/acid, displacement reactions, redox rules, rusting conditions and prevention methods, plus the required practical.

**Prerequisites:** [Writing balanced chemical equations with state symbols](https://www.owlsprep.com/study/edexcel-igcse-chemistry-s1-chemical-equations/); [Basic properties of metals](https://www.owlsprep.com/study/edexcel-igcse-chemistry-s2-properties-of-metals/)

## Learning objectives

- Arrange metals in the specified reactivity order using water, acid, and displacement reaction data
- Recall rusting conditions and 3 methods of iron rust prevention
- Define redox, oxidation, reduction, oxidising and reducing agents using oxygen and electron transfer rules
- Predict displacement reaction outcomes and write balanced equations with state symbols
- Describe the required practical for metal reactions with dilute acids

## Reactivity Series Order & Ranking from Water/Acid Reactions

**Reactivity Series** — A ranked list of metals ordered from highest reactivity (top) to lowest reactivity (bottom), determined by their tendency to form positive ions.

The Edexcel IGCSE required reactivity order is: **Potassium (K) > Sodium (Na) > Lithium (Li) > Calcium (Ca) > Magnesium (Mg) > Aluminium (Al) > Zinc (Zn) > Iron (Fe) > Copper (Cu) > Silver (Ag) > Gold (Au)**. You can rank metals by observing their reaction with cold water, steam, and dilute hydrochloric/sulfuric acid: the more vigorous the reaction, the higher the reactivity. Metals above hydrogen react with dilute acids to produce salt and hydrogen gas; metals below hydrogen do not react with dilute acids.

**Worked example:** A student adds equal sized, equal surface area pieces of metals W, X, Y to equal volumes of 1mol/dm³ dilute hydrochloric acid. W fizzes very slowly, X fizzes violently, Y has no visible change. Order the metals from most to least reactive, and identify which could be copper.

1. Faster fizzing = higher reactivity, so the order is X > W > Y.
2. Copper is below hydrogen in the reactivity series, so it does not react with dilute acid. Therefore Y is copper.

> **Exam tip**
>
> Always use the Edexcel-specified K > Na > Li order, not the order you may see in other textbooks, to avoid losing ranking marks.

*Calculator:* allowed

## Displacement Reactions & Reactivity Ranking

**Displacement Reaction** — A reaction where a more reactive metal displaces a less reactive metal from its solid metal oxide or aqueous metal salt solution.

Displacement only occurs if the added free metal is higher in the reactivity series than the metal ion in the oxide or salt. You can use observed displacement reactions to confirm the relative reactivity of two metals. Always include state symbols in balanced equations for displacement reactions, as marks are frequently awarded for correct state symbols.

**Worked example:** Write the balanced equation (with state symbols) for the reaction between zinc metal and copper(II) oxide when heated, and explain why the reaction occurs.

1. Check reactivity: Zinc is above copper in the reactivity series, so displacement occurs.
2. Products are zinc oxide and copper metal.
3. $$Zn(s) + CuO(s) \rightarrow ZnO(s) + Cu(s)$$
4. Explanation: Zinc is more reactive than copper, so it displaces copper from its oxide.

*Calculator:* allowed

## Redox Reactions & Key Definitions

**Redox Reaction** — A reaction where oxidation and reduction take place at the same time.

There are two accepted definitions for oxidation and reduction for this course: <br> 1. **Oxygen transfer**: Oxidation = gain of oxygen; Reduction = loss of oxygen <br> 2. **Electron transfer**: Oxidation = loss of electrons; Reduction = gain of electrons. The reducing agent is the substance that is oxidised, and the oxidising agent is the substance that is reduced.

> **mnemonic**
>
> OIL RIG: Oxidation Is Loss of electrons, Reduction Is Gain of electrons

**Worked example:** Identify the oxidising and reducing agent in the reaction: $Mg(s) + CuSO_4(aq) \rightarrow MgSO_4(aq) + Cu(s)$

1. Track electron transfer: Mg loses 2 electrons to form $Mg^{2+}$, so Mg is oxidised, therefore it is the reducing agent.
2. $Cu^{2+}$ gains 2 electrons to form Cu, so $Cu^{2+}$ (from $CuSO_4$) is reduced, therefore $CuSO_4$ is the oxidising agent.

*Calculator:* allowed

## Rusting of Iron & Prevention Methods

**Rusting** — The corrosion of iron to form hydrated iron(III) oxide (rust), which requires both oxygen (from air) and water to occur.

Rusting can be prevented by removing one or both required conditions: <br> 1. **Barrier methods**: Paint, oil, grease, or plastic coating blocks oxygen and water from touching the iron surface. <br> 2. **Galvanising**: Coating iron with zinc, which acts as a barrier, and if scratched, zinc is more reactive than iron so it corrodes preferentially. <br> 3. **Sacrificial protection**: Attaching a more reactive metal (e.g. magnesium, zinc) to iron, which oxidises instead of the iron, even when the iron is exposed to water and oxygen.

**Worked example:** Explain why painting an iron gate prevents it from rusting.

1. Paint forms a waterproof, airtight barrier between the iron surface and oxygen and water in the environment.
2. Since both oxygen and water are required for rusting, removing their access to iron stops rust formation.

*Calculator:* allowed

## Required Practical: Metal Reactions with Dilute Acids

This practical (spec point 2.21) investigates the relative reactivity of magnesium, zinc, and iron using their reaction with dilute hydrochloric or sulfuric acid. You must use equal volumes of the same concentration acid, and equal mass, equal surface area pieces of each metal to ensure valid results. You can measure reactivity by observing the rate of fizzing, or measuring the volume of hydrogen gas produced per minute.

**Worked example:** State the expected results of this practical, and explain what they show about the relative reactivity of the three metals.

1. Expected results: Magnesium fizzes fastest, then zinc, then iron fizzes slowest.
2. Faster reaction rate = higher reactivity, so the order is Magnesium > Zinc > Iron, matching the standard reactivity series.

*Calculator:* allowed

## Common pitfalls

- **Wrong:** Using the order Li > Na > K instead of the Edexcel-specified K > Na > Li
  - Why it fails: Edexcel explicitly requires the K > Na > Li order, so you will lose marks for incorrect ranking.
  - Correct: Memorise the exact spec reactivity order: K, Na, Li, Ca, Mg, Al, Zn, Fe, Cu, Ag, Au.
- **Wrong:** Predicting displacement when the added metal is less reactive than the metal in the salt/oxide
  - Why it fails: Displacement only occurs if the added metal is higher in the reactivity series than the metal ion present.
  - Correct: Always check the reactivity order before predicting displacement reactions.
- **Wrong:** Stating rusting only requires water or only requires oxygen
  - Why it fails: Both water and oxygen are essential for rusting to occur, as rust is hydrated iron(III) oxide.
  - Correct: Recall that both $H_2O$ and $O_2$ must be present for iron to rust; removing either stops rusting.
- **Wrong:** Confusing oxidising and reducing agents: stating the oxidising agent is oxidised
  - Why it fails: Oxidising agents cause oxidation in other substances, so they are themselves reduced.
  - Correct: Remember: reducing agent = oxidised; oxidising agent = reduced.
- **Wrong:** Forgetting state symbols in displacement reaction equations
  - Why it fails: Edexcel exam questions often explicitly award marks for correct state symbols.
  - Correct: Always include (s), (l), (g), (aq) for all reactants and products in balanced equations.
- **Wrong:** Thinking galvanising only works as a barrier method
  - Why it fails: If the zinc coating is scratched, zinc is more reactive than iron so it acts as a sacrificial metal, continuing to protect the iron.
  - Correct: Remember galvanising provides both barrier and sacrificial protection.

## Cheatsheet

| Metal | Reacts with cold water? | Reacts with dilute acid? | Displaces Cu from $CuSO_4(aq)$? |
| --- | --- | --- | --- |
| Potassium (K) | Yes (explosive) | Yes (explosive) | Yes |
| Sodium (Na) | Yes (very vigorous) | Yes (very vigorous) | Yes |
| Lithium (Li) | Yes (vigorous) | Yes (vigorous) | Yes |
| Calcium (Ca) | Yes (steady) | Yes (fast) | Yes |
| Magnesium (Mg) | Very slowly | Yes (fast fizzing) | Yes |
| Aluminium (Al) | No | Yes (slow initially) | Yes |
| Zinc (Zn) | No | Yes (steady fizzing) | Yes |
| Iron (Fe) | No | Yes (slow fizzing) | Yes |
| Copper (Cu) | No | No | No |
| Silver (Ag) | No | No | No |
| Gold (Au) | No | No | No |

## What's next

Now that you have mastered the reactivity series, you can move on to related core topics that build directly on this knowledge. The next sub-topic is metal extraction, which uses the reactivity series to determine the correct method for extracting different metals from their ores. You will also apply the redox rules you learned here to electrolysis reactions, where oxidation and reduction occur at electrodes. Practicing past paper questions on reactivity ranking, displacement reactions, and rust prevention will help you solidify your understanding and avoid common exam mistakes.

- [Electrolysis & Redox](https://www.owlsprep.com/study/edexcel-igcse-chemistry-s1-electrolysis/)

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