Reactivity series

1. Overview

The reactivity series is a ranking of metals based on their chemical reactivity, specifically their ability to lose electrons and form positive ions. Understanding this order allows us to predict how metals will behave in chemical reactions, how they are extracted from their ores, and their suitability for various real-world applications.

Key Definitions

• Reactivity Series: A list of metals (and some non-metals like carbon and hydrogen) arranged in order of their chemical reactivity, from most reactive to least reactive.
• Displacement Reaction: A reaction in which a more reactive element takes the place of a less reactive element in a compound.
• Oxidation: The gain of oxygen (Core) or the loss of electrons (Supplement).
• Reduction: The loss of oxygen (Core) or the gain of electrons (Supplement).

---

Core Content

The Order of the Reactivity Series

You must memorize this order (from most to least reactive):

1. Potassium (K)
2. Sodium (Na)
3. Calcium (Ca)
4. Magnesium (Mg)
5. Aluminium (Al)
6. Carbon (C) - Non-metal reference
7. Zinc (Zn)
8. Iron (Fe)
9. Hydrogen (H) - Non-metal reference
10. Copper (Cu)
11. Silver (Ag)
12. Gold (Au)

(a) Reactions with Cold Water

Only the most reactive metals react with cold water to produce a metal hydroxide and hydrogen gas.

• Potassium: Reacts violently; produces a lilac flame.
• Sodium: Reacts vigorously; fizzes and melts into a ball.
• Calcium: Reacts steadily; the water becomes cloudy as calcium hydroxide forms.

General Equation: Metal(s) + Water(l) → Metal Hydroxide(aq) + Hydrogen(g) Example (Sodium): Sodium + Water → Sodium hydroxide + Hydrogen 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)

(b) Magnesium with Steam

Magnesium reacts very slowly with cold water but reacts vigorously with steam to produce a metal oxide and hydrogen. Equation: Magnesium + Water (steam) → Magnesium oxide + Hydrogen Mg(s) + H₂O(g) → MgO(s) + H₂(g)

(c) Reactions with Dilute Hydrochloric Acid

Metals above hydrogen in the series react with acid to produce a salt and hydrogen gas.

• Magnesium: Fast reaction, lots of bubbles.
• Zinc & Iron: Slower reactions.
• Copper, Silver, Gold: No reaction (they are below hydrogen).

General Equation: Metal(s) + Hydrochloric Acid(aq) → Metal Chloride(aq) + Hydrogen(g) Example (Zinc): Zinc + Hydrochloric acid → Zinc chloride + Hydrogen Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)

Displacement Reactions — Predicting What Happens

The rule is simple: a more reactive metal will displace a less reactive metal from its compound. If it’s less reactive, nothing happens.

Worked Example: Will zinc displace copper from copper sulfate solution?

1. Check the reactivity series: Zinc is above Copper.
2. Since zinc is more reactive, it will displace copper.
3. Equation: $Zn(s) + CuSO_4(aq) \rightarrow ZnSO_4(aq) + Cu(s)$
4. You would see: the blue solution turns colourless, and a brown-orange coating of copper appears on the zinc.

Will copper displace zinc from zinc sulfate? No — copper is below zinc in the reactivity series. A less reactive metal cannot push out a more reactive one. No reaction occurs.

This pattern also works for carbon and hydrogen:

• Carbon can reduce (extract) metals below it in the series (zinc, iron, copper) but not those above it (aluminium, magnesium).
• Metals above carbon need electrolysis to extract them.

Deducing Order from Experimental Results

If an "Unknown Metal X" reacts with acid but "Unknown Metal Y" does not, Metal X is higher in the reactivity series than Metal Y. We use the rate of bubble production (hydrogen) or temperature change to determine the specific rank.

---

Extended Content (Extended curriculum only)

Tendency to Form Positive Ions

Reactivity is defined by how easily a metal atom loses its outer shell electrons to form a positive ion (cation).

• Potassium (High reactivity): Loses its electron very easily to become K⁺.
• Copper (Low reactivity): Does not lose electrons easily.

Displacement Reactions

A more reactive metal will displace a less reactive metal from its aqueous salt solution. Example: Zinc is more reactive than Copper. Zinc + Copper(II) sulfate → Zinc sulfate + Copper Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)

Ionic Equation (showing electron transfer): Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s)

• The Zinc atom is oxidized (loses 2 electrons).
• The Copper ion is reduced (gains 2 electrons).

The Apparent Unreactivity of Aluminium

Aluminium is high in the reactivity series, yet it does not react with water and reacts very slowly with acids.

• Reason: Aluminium reacts rapidly with oxygen in the air to form a very thin, tough, and unreactive layer of Aluminium Oxide (Al₂O₃).
• This oxide layer sticks strongly to the metal surface, acting as a protective barrier that prevents water or acids from reaching the metal underneath.

---

Key Equations

Reaction Type	Word Equation	Balanced Symbol Equation
Metal + Water	Metal + Water → Hydroxide + Hydrogen	2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)
Metal + Steam	Metal + Steam → Oxide + Hydrogen	Mg(s) + H₂O(g) → MgO(s) + H₂(g)
Metal + Acid	Metal + Acid → Salt + Hydrogen	Fe(s) + 2HCl(aq) → FeCl₂(aq) + H₂(g)
Displacement	Metal A + Metal B Salt → Metal A Salt + Metal B	Mg(s) + FeSO₄(aq) → MgSO₄(aq) + Fe(s)

Symbols: (s) solid, (l) liquid, (g) gas, (aq) aqueous/dissolved in water.

---

Common Mistakes to Avoid

• ❌ Wrong: Writing that Magnesium + Water makes Magnesium Hydroxide in the steam reaction.
• ✓ Right: Magnesium + Steam makes Magnesium Oxide (MgO). Hydroxides are usually formed with cold water.
• ❌ Wrong: Thinking Aluminium is at the bottom of the series because it doesn't react.
• ✓ Right: Aluminium is very reactive, but it is protected by an oxide layer.
• ❌ Wrong: Forgetting state symbols in equations.
• ✓ Right: Always include (s), (l), (g), or (aq) as requested by IGCSE guidelines.

---

Exam Tips

• Command Words: When asked to "State," provide a brief fact (e.g., "State the gas produced: Hydrogen"). When asked to "Explain," give reasons using the reactivity series (e.g., "Copper does not react because it is below hydrogen in the reactivity series").
• Unknown Metals: Exams often give you "Metal X, Y, and Z" and their reactions. Use a "knock-out" system to rank them from most to least reactive.
• Contexts: Laboratory observations are common. If you see "effervescence," the gas is likely hydrogen (test with a lighted splint for a "squeaky pop").
• Typical Values: In thermochemistry questions related to reactivity, a temperature rise of 3.1°C might be used to compare the energy released by different metals in displacement reactions. Higher temperature rise = more reactive metal.

---

Exam-Style Questions

Practice these original exam-style questions to test your understanding. Each question mirrors the style, structure, and mark allocation of real Cambridge 0620 Theory papers.

Exam-Style Question 1 — Short Answer [5 marks]

Question:

(a) Define the term displacement reaction. [1]

(b) A student adds a piece of zinc metal to aqueous copper(II) sulfate. Describe what the student would observe. [2]

(c) Write a balanced chemical equation, including state symbols, for the reaction in (b). [2]

Worked Solution:

(a)

1. A displacement reaction is a reaction in which a more reactive element replaces a less reactive element from its compound. $\boxed{\text{See above}}$ Definition of displacement reaction.

How to earn full marks:

• Correct definition of "displacement" involving a more reactive element taking the place of a less reactive element from its compound.

(b)

1. The blue colour of the copper(II) sulfate solution will fade. $\boxed{\text{Blue colour fades}}$ Observation of the change in colour of the solution.
2. A pink/brown solid (copper) will form. $\boxed{\text{Pink/brown solid forms}}$ Observation of the formation of a solid.

How to earn full marks:

• 1 mark for mentioning the fading of the blue colour.
• 1 mark for mentioning the formation of a pink/brown solid.

(c)

1. The correct reactants and products must be present. $Zn(s) + CuSO_4(aq) \rightarrow Cu(s) + ZnSO_4(aq)$ Correct chemical equation.
2. The equation must be balanced and include correct state symbols. $\boxed{Zn(s) + CuSO_4(aq) \rightarrow Cu(s) + ZnSO_4(aq)}$ Fully correct equation.

How to earn full marks:

• 1 mark for the correct chemical formulas and balanced equation.
• 1 mark for correct state symbols.

Common Pitfall: Many students forget to include state symbols in their equations, which can cost them a mark. Also, make sure you know the colours of common ions in solution, like copper(II) ions.

Exam-Style Question 2 — Short Answer [6 marks]

Question:

(a) State the order of the following metals in terms of their reactivity, from most reactive to least reactive: iron, magnesium, copper, potassium. [2]

(b) Describe the reaction, if any, of potassium with cold water. Include a balanced chemical equation. [4]

Worked Solution:

(a)

1. Potassium is the most reactive metal. $\boxed{\text{Potassium}}$ Correct identification of the most reactive metal.
2. The full reactivity series stated correctly. $\boxed{\text{Potassium, Magnesium, Iron, Copper}}$ Correct series.

How to earn full marks:

• 1 mark for correctly identifying potassium as the most reactive.
• 1 mark for the correct order of all four metals.

(b)

1. Potassium reacts vigorously with cold water. $\boxed{\text{Reacts vigorously}}$ Description of the reaction rate.
2. The reaction produces hydrogen gas. $\boxed{\text{Hydrogen gas produced}}$ Identification of a gaseous product.
3. The reaction produces potassium hydroxide. $\boxed{\text{Potassium hydroxide produced}}$ Identification of the other product.
4. Correct balanced chemical equation. $\boxed{2K(s) + 2H_2O(l) \rightarrow 2KOH(aq) + H_2(g)}$ Fully correct equation.

How to earn full marks:

• 1 mark for describing the reaction as vigorous/violent.
• 1 mark for identifying hydrogen gas as a product.
• 1 mark for identifying potassium hydroxide as a product.
• 1 mark for the correctly balanced equation including state symbols.

Common Pitfall: Students often struggle to remember the reactivity of potassium, sodium, and calcium with water. Make sure you know that these metals react with cold water, and the reaction is more vigorous as you go up the group.

Exam-Style Question 3 — Extended Response [8 marks]

Question:

A student investigates the reactivity of three metals: nickel, tin, and zinc. They place each metal separately into aqueous solutions of the other metal nitrates. The table below shows their observations.

Metal	Nickel(II) nitrate	Tin(II) nitrate	Zinc nitrate
Nickel	No reaction	Reaction	No reaction
Tin	No reaction	No reaction	No reaction
Zinc	Reaction	Reaction	No reaction

(a) Deduce the order of reactivity of the three metals, from most reactive to least reactive. Explain your reasoning. [4]

(b) Write an ionic equation for the reaction between zinc and nickel(II) nitrate. [2]

(c) Suggest why the student used metal nitrates rather than metal chlorides in this experiment. [2]

Worked Solution:

(a)

1. Zinc is the most reactive because it reacts with both nickel(II) nitrate and tin(II) nitrate. $\boxed{\text{Zinc is most reactive}}$ Identification of the most reactive metal.
2. Tin is the least reactive because it does not react with any of the metal nitrate solutions. $\boxed{\text{Tin is least reactive}}$ Identification of the least reactive metal.
3. Nickel is more reactive than tin but less reactive than zinc, because nickel reacts with tin(II) nitrate but not with zinc nitrate. $\boxed{\text{Nickel is in the middle}}$ Correct placement of nickel in the series.
4. Therefore, the order of reactivity is: Zinc, Nickel, Tin. $\boxed{\text{Zinc > Nickel > Tin}}$ Correct series.

How to earn full marks:

• 1 mark for identifying zinc as the most reactive metal, justifying with reference to the table.
• 1 mark for identifying tin as the least reactive metal, justifying with reference to the table.
• 1 mark for placing nickel correctly between zinc and tin, justifying with reference to the table.
• 1 mark for stating the correct order of reactivity.

(b)

1. Correct identification of the reacting ions. $Zn(s) + Ni^{2+}(aq) \rightarrow Ni(s) + Zn^{2+}(aq)$ Correct ions.
2. Correctly balanced ionic equation, including state symbols and charges. $\boxed{Zn(s) + Ni^{2+}(aq) \rightarrow Ni(s) + Zn^{2+}(aq)}$ Balanced equation.

How to earn full marks:

• 1 mark for the correct ions involved in the reaction.
• 1 mark for the balanced ionic equation, including charges and state symbols.

(c)

1. Metal chlorides could react with the metal ions to form precipitates. $\boxed{\text{Chloride ions might form precipitates}}$ Identification of the potential for precipitation.
2. This would interfere with observations of the displacement reactions. $\boxed{\text{Precipitates would interfere with observations}}$ Explanation of the interference.

How to earn full marks:

• 1 mark for suggesting that chloride ions might form precipitates.
• 1 mark for explaining that these precipitates would obscure the observations of displacement reactions.

Common Pitfall: When deducing reactivity from experimental results, make sure you clearly state why a metal is more or less reactive based on the reactions observed. Just stating the order without justification won't get you full marks.

Exam-Style Question 4 — Extended Response [10 marks]

Question:

A student investigates the reaction of different metals with dilute hydrochloric acid. They use magnesium, iron, and copper.

(a) Describe the expected observations when each metal is separately added to dilute hydrochloric acid. [3]

(b) The student collects the gas produced when magnesium reacts with dilute hydrochloric acid. Describe a test to identify this gas. [2]

(c) Explain why copper does not react with dilute hydrochloric acid, whereas magnesium and iron do react. [3]

(d) A student wants to compare the rate of reaction of magnesium and iron with dilute hydrochloric acid. Plan an experiment to do this, ensuring a fair test. Include details of the apparatus, measurements, and how to ensure the test is fair. [2]

Worked Solution:

(a)

1. Magnesium reacts vigorously, producing bubbles of gas and the metal dissolves. $\boxed{\text{Magnesium: vigorous bubbling, metal dissolves}}$ Description of magnesium's reaction.
2. Iron reacts slowly, producing bubbles of gas and the metal dissolves. $\boxed{\text{Iron: slow bubbling, metal dissolves}}$ Description of iron's reaction.
3. Copper does not react, no bubbles of gas are produced, and the metal does not dissolve. $\boxed{\text{Copper: no reaction}}$ Description of copper's reaction.

How to earn full marks:

• 1 mark for each correct description of the reaction of each metal with dilute hydrochloric acid.

(b)

1. Collect the gas in a test tube. $\boxed{\text{Collect gas in a test tube}}$ Collection of gas.
2. Insert a lit splint into the test tube. If hydrogen is present, it will 'pop'. $\boxed{\text{Insert lit splint, 'pop' sound indicates hydrogen}}$ Description of the test.

How to earn full marks:

• 1 mark for describing collecting the gas.
• 1 mark for describing the "pop" test with a lit splint.

(c)

1. Magnesium and iron are more reactive than hydrogen. $\boxed{\text{Mg and Fe more reactive than H}}$ Reactivity relative to hydrogen.
2. They can displace hydrogen ions ($H^+$) from the acid to form hydrogen gas. $\boxed{\text{Displace H+ to form hydrogen}}$ Explanation of displacement.
3. Copper is less reactive than hydrogen and cannot displace hydrogen ions from the acid. $\boxed{\text{Cu less reactive than H, cannot displace}}$ Explanation of copper's unreactivity.

How to earn full marks:

• 1 mark for stating that magnesium and iron are more reactive than hydrogen.
• 1 mark for explaining that they displace hydrogen ions from the acid.
• 1 mark for stating that copper is less reactive than hydrogen and cannot displace hydrogen ions.

(d)

1. Use the same mass of each metal (magnesium and iron) in powdered form and the same volume and concentration of dilute hydrochloric acid. $\boxed{\text{Equal mass of powdered metal, same volume/concentration of HCl}}$ Controlled variables.
2. Measure the volume of gas produced over time using a gas syringe, or measure the mass loss over time using a balance. $\boxed{\text{Measure gas volume or mass loss over time}}$ Measurement method.

How to earn full marks:

• 1 mark for stating that the same mass of each metal in powdered form and the same volume and concentration of acid should be used.
• 1 mark for describing how to measure the rate of reaction (e.g., volume of gas produced over time).

Common Pitfall: When planning experiments, remember to explicitly state the variables you'll keep constant to ensure a fair test. Also, be specific about how you'll measure the rate of reaction, not just that you'll "measure the reaction."