GCSE Chemistry - How to Solve: Reactivity Series and Metal Extraction Reactions

How to Solve: Reactivity Series and Metal Extraction Reactions

Complete Guide For GCSE/A-Level Chemistry (AQA, Edexcel, OCR, WJEC)

Introduction

"Mastering the reactivity series lets you predict which metals explode in water, which rust fastest, and how to extract gold from rock—worth up to 12 marks in your GCSE Chemistry exam and a guaranteed question in A-Level Paper 1."

WHAT YOU NEED TO KNOW FIRST

1. Atomic structure: Protons, neutrons, electrons, and how metals lose electrons to form positive ions.
2. Redox reactions: Oxidation = loss of electrons; reduction = gain of electrons (OIL RIG).
3. Displacement reactions: A more reactive metal displaces a less reactive metal from its compound.

KEY TERMS & FORMULAS

Key Terms

Formulas & Equations

1. General displacement reaction: More reactive metal + Less reactive metal compound → More reactive metal compound + Less reactive metal Example: Zn + CuSO₄ → ZnSO₄ + Cu

2. Reduction of metal oxides (using carbon): Metal oxide + Carbon → Metal + Carbon dioxide Example: 2Fe₂O₃ + 3C → 4Fe + 3CO₂

3. MEMORISE THIS: Only works for metals below carbon in the reactivity series.

4. Electrolysis of molten metal compounds: Metal compound → Metal + Non-metal (at electrodes) Example: 2Al₂O₃ → 4Al + 3O₂ (aluminium extraction)

5. MEMORISE THIS: Used for metals above carbon (e.g., Al, Na, Ca).

6. Reactivity series (MEMORISE THIS ORDER): K > Na > Ca > Mg > Al > C > Zn > Fe > Sn > Pb > H > Cu > Ag > Au > Pt

7. Mnemonic: "Please Stop Calling Me A Careless Zebra Instead Try Learning How Copper Saves Gold Platinum"

STEP-BY-STEP METHOD

Step 1: Identify the metal and its position in the reactivity series

• Use the memorised reactivity series (above).
• If the metal is above carbon (Al, Mg, Ca, Na, K), it cannot be extracted using carbon. Electrolysis is required.
• If the metal is below carbon (Zn, Fe, Sn, Pb, Cu), it can be extracted using carbon (reduction).

Step 2: Determine the extraction method

Step 3: Write the balanced equation (if required)

• For carbon reduction:
• Metal oxide + Carbon → Metal + Carbon dioxide
• Balance the equation (e.g., Fe₂O₃ + 3CO → 2Fe + 3CO₂).
• For electrolysis:
• Write the half-equations for the cathode (reduction) and anode (oxidation).
• Example (Al₂O₃):
  • Cathode: Al³⁺ + 3e⁻ → Al
  • Anode: 2O²⁻ → O₂ + 4e⁻

Step 4: Predict displacement reactions

• A more reactive metal will displace a less reactive metal from its compound.
• Example: Will magnesium react with copper sulfate?
• Mg is above Cu in the reactivity series → Yes.
• Equation: Mg + CuSO₄ → MgSO₄ + Cu

Step 5: Explain real-world applications

• Blast furnace (iron extraction): Used for Fe (below carbon).
• Electrolysis (aluminium extraction): Used for Al (above carbon).
• Displacement reactions: Used in galvanising (Zn coating on Fe to prevent rust).

WORKED EXAMPLES

Example 1 – Basic: Predicting a Displacement Reaction

Question: Will zinc react with silver nitrate solution? Write the balanced equation.

Step-by-Step Solution:
1. Check reactivity series: - Zn is above Ag → Yes, reaction occurs.
2. Write the displacement reaction: - Zn + AgNO₃ → Zn(NO₃)₂ + Ag
3. Balance the equation: - Zn + 2AgNO₃ → Zn(NO₃)₂ + 2Ag

What we did and why: - We compared Zn and Ag in the reactivity series. - Since Zn is more reactive, it displaces Ag from AgNO₃. - Balancing ensures the same number of atoms on both sides.

Example 2 – Medium: Choosing an Extraction Method

Question: How is calcium extracted from its ore? Explain why carbon cannot be used.

Step-by-Step Solution:
1. Find Ca in the reactivity series: - Ca is above carbon (K > Na > Ca > Mg > Al > C).
2. Determine extraction method: - Electrolysis is required (carbon reduction won’t work).
3. Explain why carbon fails: - Carbon is less reactive than Ca → cannot remove oxygen from CaO.
4. Write the electrolysis half-equations: - Cathode: Ca²⁺ + 2e⁻ → Ca - Anode: 2O²⁻ → O₂ + 4e⁻

What we did and why: - We used the reactivity series to rule out carbon reduction. - Electrolysis is the only method for metals above carbon. - Half-equations show the electron transfer at each electrode.

Example 3 – Exam-Style: Explaining Rusting and Prevention

Question (6 marks): "Explain why iron rusts faster than copper and how galvanising prevents rusting. Include equations where relevant."

Step-by-Step Solution:
1. Compare reactivity: - Fe is above Cu in the reactivity series → more reactive. - More reactive metals lose electrons faster → rust (oxidise) quicker.
2. Rusting equation (iron): - 4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃ (hydrated iron(III) oxide = rust).
3. Galvanising explanation: - Coating Fe with Zn (more reactive than Fe). - Zn sacrificially oxidises instead of Fe.
4. Displacement reaction: - Zn + Fe²⁺ → Zn²⁺ + Fe (Zn corrodes first, protecting Fe).

What we did and why: - We linked reactivity to rusting speed (higher reactivity = faster corrosion). - Galvanising works because Zn is more reactive than Fe, so it "sacrifices" itself. - The equation shows Zn displacing Fe²⁺, preventing Fe from rusting.

COMMON MISTAKES

EXAM TRAPS

1-MINUTE RECAP

"Right, listen up—this is your last-minute cheat sheet for reactivity series and metal extraction. First, memorise the reactivity series—K to Pt, no excuses. If a metal is above carbon, it needs electrolysis; if it’s below, carbon reduction works. Displacement reactions? The more reactive metal wins—always. Rusting? Iron’s more reactive than copper, so it rusts faster. Galvanising? Zinc sacrifices itself to save iron. Equations? Balance them, and for electrolysis, remember: cathode = reduction, anode = oxidation. And if the exam asks why carbon can’t extract sodium, it’s because sodium’s above carbon—boom, easy marks. Now go smash it!"