Reactivity
Section: Chemistry | Syllabus: Cambridge Lower Secondary Checkpoint Science (0893)
The Reactivity Series
- The reactivity series is a list of metals arranged in order of their reactivity
- The most reactive metals are at the top, and the least reactive are at the bottom
- Reactivity series: a list of metals arranged in order of their reactivity, with the most reactive at the top and the least reactive at the bottom
Order of Reactivity (Most to Least Reactive)
- Caesium (Cs) - most reactive
- Rubidium (Rb) - more reactive than potassium
- Potassium (K)
- Sodium (Na)
- Calcium (Ca)
- Magnesium (Mg)
- Aluminium (Al)
- CARBON (C) - non-metal (for comparison)
- Zinc (Zn)
- Iron (Fe)
- Tin (Sn)
- Lead (Pb)
- HYDROGEN (H) - non-metal (for comparison)
- Copper (Cu)
- Silver (Ag)
- Gold (Au) - least reactive
The reactivity series, from most reactive to least reactive
- Memory aid: Please Send Charlie's Monkeys And Zebras In Lead Tanks Heavily Guarded By Security
- Potassium, Sodium, Calcium, Magnesium, Aluminium, Zinc, Iron, Lead, Tin, Hydrogen, Copper, Silver, Gold
What Does Reactivity Mean?
- More reactive metals react more vigorously and more quickly
- More reactive metals lose electrons more easily to form positive ions
- Less reactive metals are more stable and harder to react
Evidence for the Reactivity Series
Reactions with Water
- Potassium, sodium, calcium: react vigorously with cold water, producing hydrogen gas and metal hydroxide
- Magnesium: reacts slowly with cold water but vigorously with steam
- Zinc, iron: react with steam but not cold water
- Copper, silver, gold: do not react with water or steam
- The flame colour produced can be used to help identify which Group 1 metal is reacting with water: sodium burns with a yellow/orange flame, while potassium burns with a lilac (pink) flame and reacts more quickly than sodium, since it is more reactive
Safety When Demonstrating Reactive Metals
- Reactions of Group 1 metals with water can be vigorous and produce flammable hydrogen gas, so demonstrations must be done safely:
- carry out the demonstration behind a safety screen or in a fume cupboard
- wear safety goggles and a laboratory coat
- only use a small piece of the metal, handled with tweezers, and stand well back
Recognising and Completing Symbol Equations
- For well-known reactions, such as an alkali metal reacting with water, a symbol equation may already be given in a balanced form, or you may be asked to complete missing formulae within one - you are not expected to balance an equation from scratch
- Even without balancing, credit is given for writing the correct formulae of the reactants and products
Worked Example: Symbol Equation for Potassium + Water
A teacher adds potassium, K, to water, H₂O, making potassium hydroxide, KOH, and hydrogen, H₂.
- Step 1: write the correct formula for each reactant and product: K, H₂O, KOH, H₂
- Step 2: writing K + H₂O → KOH + H₂ already earns credit, since the formulae are correct even though this version is not balanced
- Step 3: to complete the balanced equation, check that the number of each atom matches on both sides: 2K + 2H₂O → 2KOH + H₂
Reactions with Dilute Acids
- Very reactive metals (above hydrogen): react vigorously with dilute acids, producing hydrogen gas and a salt
- Less reactive metals (below hydrogen): do not react with dilute acids
Exam Tip
- Only metals above hydrogen in the reactivity series will react with dilute acids to produce hydrogen gas
Displacement Reactions
- A displacement reaction is where a more reactive metal pushes out a less reactive metal from its compound
- This occurs because the more reactive metal has a stronger tendency to form ions
- Displacement reaction: a reaction where a more reactive metal pushes out (displaces) a less reactive metal from its compound
The Displacement Rule
- A more reactive metal will displace a less reactive metal from its compound
- This works with both salt solutions and metal oxides
How Displacement Works
- The more reactive metal loses electrons (gets oxidised) to form ions
- The less reactive metal gains electrons (gets reduced) and becomes a pure metal
- The more reactive metal takes the place of the less reactive metal in the compound
Examples of Displacement Reactions
Museli reacts magnesium with copper sulfate solution. Magnesium is more reactive than copper, so it displaces copper.
- Word equation: Magnesium + Copper sulfate → Magnesium sulfate + Copper
- What you see: the blue solution turns colourless, and brown copper metal appears
Muumbe reacts zinc with iron sulfate solution. Zinc is more reactive than iron, so displacement occurs.
- Word equation: Zinc + Iron sulfate → Zinc sulfate + Iron
- What you see: grey iron metal forms
Muchindu reacts copper with silver nitrate solution. Copper is more reactive than silver, so displacement occurs.
- Word equation: Copper + Silver nitrate → Copper nitrate + Silver
- What you see: silver crystals form on the copper, solution turns blue
Museli reacts zinc with gold nitrate solution. Zinc is more reactive than gold, so displacement occurs.
- Word equation: Zinc + Gold nitrate → Zinc nitrate + Gold
- What you see: gold metal is deposited out of solution
Muumbe reacts calcium with copper sulfate solution. Calcium is more reactive than copper, so displacement occurs.
- Word equation: Calcium + Copper sulfate → Calcium sulfate + Copper
- What you see: brown copper metal is deposited out of solution
No Reaction Example: Muchindu tries reacting copper with magnesium sulfate solution. Copper is less reactive than magnesium, so NO displacement occurs.
- Copper + Magnesium sulfate → NO REACTION
- Copper cannot displace magnesium because it is less reactive
Interactive revision notes, videos and practice questions load below.