👋 Welcome to the World of Reactivity!
Hello future chemist! This chapter is incredibly important because it explains why some metals are stored under oil while others sit happily as jewellery on your finger.
We are going to learn about the Reactivity Series—a simple ranking system that predicts how different metals will behave when they meet water, acids, or other metal compounds. Don't worry if this seems tricky at first; we’ll break it down using simple analogies and awesome memory tricks!
🔬 Section 1: What Exactly is Reactivity?
In chemistry, the reactivity of a metal refers to how easily that metal reacts, usually by losing its outer electrons to form positive ions.
Think of it like a competitive race.
- A highly reactive metal (like Potassium) is desperate to lose its electrons and react quickly. It wins the race easily!
- A low reactivity metal (like Gold) holds onto its electrons tightly and barely reacts at all. It doesn't even want to participate in the race.
The Key Takeaway: The higher a metal is placed in the reactivity series, the more easily it forms positive ions and the more vigorous its reactions are.
Quick Review Box: Reactivity vs. Electrons
High Reactivity = Easy to lose electrons
Low Reactivity = Hard to lose electrons (Stable)
💡 Section 2: The Order of the Reactivity Series
The reactivity series arranges common metals from the most reactive (top) to the least reactive (bottom). We also include Carbon and Hydrogen in the series, even though they are non-metals, because they help us understand extraction methods and reactions with acids.
The Official IGCSE Reactivity Series List
Here is the list you must learn. We’ve put the most reactive at the top:
- Potassium (K) - Most reactive
- Sodium (Na)
- Calcium (Ca)
- Magnesium (Mg)
- Aluminium (Al)
- Carbon (C) - (Used for extraction)
- Zinc (Zn)
- Iron (Fe)
- Lead (Pb)
- Hydrogen (H) - (Used for acid comparisons)
- Copper (Cu)
- Silver (Ag)
- Gold (Au) - Least reactive
🚀 Memory Aid: The Ultimate Mnemonic!
Use this simple phrase to remember the order. The first letter of each word corresponds to the chemical symbol above:
Please Stop Calling Me A Careless Zebra Instead Look How Clever Some Gold.
(Potassium, Sodium, Calcium, Magnesium, Aluminium, Carbon, Zinc, Iron, Lead, Hydrogen, Copper, Silver, Gold)
Did you know? Potassium and Sodium are so reactive that they must be stored under oil in the laboratory to prevent them reacting explosively with oxygen and water vapour in the air!
🌊 Section 3: Reactivity with Water and Acids
We can test a metal's position in the series by seeing how it reacts with water (H₂O) and dilute acids (like HCl). The more vigorous the reaction, the higher the metal is!
3.1 Reactions with Water (H₂O)
The type of reaction depends heavily on the metal’s position:
A) Highly Reactive Metals (K, Na, Ca)
- Reaction: React vigorously with cold water.
- Products: Metal hydroxide + Hydrogen gas.
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Example: Sodium reacts quickly, often melting into a ball and fizzing intensely.
\(2Na (s) + 2H_2O (l) \rightarrow 2NaOH (aq) + H_2 (g)\)
B) Medium Reactivity Metals (Mg, Al, Zn, Fe)
- Reaction: Do not react with cold water. They require steam (very hot water vapour).
- Products: Metal oxide + Hydrogen gas.
-
Example: Heating Magnesium metal strongly in steam.
\(Mg (s) + H_2O (g) \rightarrow MgO (s) + H_2 (g)\)
- Important Note for Aluminium (Al): Aluminium seems less reactive than Magnesium, but that is misleading! Al has a strong, protective layer of aluminium oxide (Al₂O₃) on its surface. This layer stops the water or acid from reaching the metal underneath. Once this layer is removed, Al is very reactive.
C) Low Reactivity Metals (Pb, Cu, Ag, Au)
- Reaction: No reaction, even with steam.
3.2 Reactions with Dilute Acids (e.g., HCl, H₂SO₄)
Most metals above Hydrogen in the series will react with dilute acids.
- General Rule: Metal + Acid → Salt + Hydrogen Gas
- The closer the metal is to the top (K, Na), the faster and more explosive the reaction will be.
- Metals like Potassium and Sodium react so violently with acids that they are rarely tested in a school lab for safety reasons.
- Metals like Copper, Silver, and Gold are below Hydrogen, so they cannot displace the hydrogen from the acid. Therefore, they do not react.
Example: Reaction between Zinc (Zn) and Hydrochloric acid (HCl).
\(Zn (s) + 2HCl (aq) \rightarrow ZnCl_2 (aq) + H_2 (g)\)
🔑 Key Takeaway for Reactions
If a metal is reactive enough, it "pushes" the Hydrogen out of the water or acid to form a new compound, always releasing Hydrogen gas (H₂).
🔄 Section 4: Displacement Reactions (The Stronger Wins)
This is one of the most important concepts of the reactivity series. A displacement reaction occurs when a more reactive metal takes the place of a less reactive metal in a compound (usually a salt solution).
Analogy: The Stronger Partner
Imagine you have Metal A and a compound of Metal B (B-Salty). If Metal A is more reactive (stronger) than Metal B, Metal A will kick Metal B out and steal its partner (Salty) to form a new compound (A-Salty).
The Rule: A more reactive metal will displace a less reactive metal from an aqueous solution of its salt.
Step-by-Step Displacement Example
Let's mix Iron (Fe) (a moderately reactive metal) with a solution of Copper Sulfate (CuSO₄) (where Copper is less reactive).
- Compare Reactivity: Iron (Fe) is higher than Copper (Cu) in the series. Iron is the "stronger partner."
- Reaction Occurs: Iron displaces Copper.
- Observation: The blue colour of the Copper Sulfate solution disappears (as CuSO₄ is consumed), and a reddish-brown solid (pure Copper metal) forms on the iron metal.
\(Fe (s) + CuSO_4 (aq) \rightarrow FeSO_4 (aq) + Cu (s)\)
Common Mistake to Avoid!
If you mix a less reactive metal with the salt of a more reactive metal (e.g., Copper metal with Iron Sulfate solution), NO REACTION will occur. The weaker metal cannot displace the stronger one.
🔥 Section 5: Using Reactivity to Extract Metals
Most metals are found in the Earth's crust as ores—compounds (usually oxides) combined with other elements. We must use energy to get the pure metal back. The method we use depends entirely on the metal's position in the reactivity series!
5.1 Metals Below Carbon (Zn, Fe, Pb, Cu)
Since these metals are less reactive than Carbon, Carbon can displace them from their oxides. This process is called reduction.
- Method: Heating the metal oxide with Carbon (usually in the form of coke or coal).
- Cost: Relatively cheap, used widely in industry (like blast furnaces for Iron).
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Example: Heating Zinc Oxide (ZnO) with Carbon (C):
\(2ZnO (s) + C (s) \rightarrow 2Zn (l) + CO_2 (g)\)
5.2 Metals Above Carbon (K, Na, Ca, Mg, Al)
These metals are more reactive than Carbon, meaning Carbon cannot reduce their oxides. They hold onto their oxygen partner too strongly!
- Method: We must use Electrolysis (passing an electric current through the molten metal compound).
- Cost: Very expensive and energy-intensive.
- Example: Aluminium is extracted from its ore (bauxite) using massive amounts of electricity.
Did you know? (Aluminium)
Because Aluminium is extracted using the very expensive process of electrolysis, it used to be considered a luxury metal more valuable than Gold, even though it is very common in the Earth's crust!
✅ Chapter Summary: Quick Review
Here are the absolute must-know facts from this chapter:
The Rank: Most Reactive (K, Na, Ca) to Least Reactive (Ag, Au).
The Purpose: Predicts how a metal will react (vigour) and how it must be extracted.
Reactions Checklist:
- Metals above H: React with acids to produce Hydrogen gas.
- Metals above C: Require expensive Electrolysis for extraction.
- Metals below C: Can be reduced cheaply using Carbon.
- Displacement: Stronger metal always kicks out the weaker metal from its salt solution.
You've done a fantastic job mastering the Reactivity Series! Keep practising that mnemonic and checking the position of the metals, and you'll be able to predict any reaction thrown your way!