Ch 15 chem - Reactivity of Metals

Group I Metals

Reactions with Water (Overview)

  • Lithium (Li): Reacts steadily with water.
    Reaction: 2Li + 2H₂O → 2LiOH + H₂
    Produces lithium hydroxide and hydrogen gas.

  • Sodium (Na): Reacts strongly with water.
    Reaction: 2Na + 2H₂O → 2NaOH + H₂
    Produces sodium hydroxide and hydrogen gas.

  • Potassium (K): Reacts violently with water.
    Reaction: 2K + 2H₂O → 2KOH + H₂
    Produces potassium hydroxide and hydrogen gas.

Summary of Reactivity of Group I Metals

Reactivity increases down the group:

  • Most Reactive: Potassium

  • Medium Reactive: Sodium

  • Least Reactive: Lithium

Group II Metals

General Trends

  • Less reactive than Group I metals, but reactivity still increases down the group.

Reactions with Water

  • Magnesium (Mg): Reacts very slowly with cold water, forming hydrogen gas slowly.
    Reaction with steam: Mg + H₂O (steam) → MgO + H₂
    Glows brightly and forms magnesium oxide and hydrogen.

  • Calcium (Ca): Reacts vigorously with cold water.
    Reaction: Ca + 2H₂O → Ca(OH)₂ + H₂
    Produces calcium hydroxide (soluble) and hydrogen gas.

Reactivity Series of Metals

From most to least reactive:

  • Potassium (K)

  • Sodium (Na)

  • Calcium (Ca)

  • Zinc (Zn)

  • Iron (Fe)

  • Copper (Cu)

  • Silver (Ag)

  • Gold (Au)

Reactions with Dilute Acids

General Reaction Format:
Metal + Acid → Metal Salt + Hydrogen

Examples:

  • Magnesium + HCl
    Reaction: Mg + 2HCl → MgCl₂ + H₂
    Strong reaction, bubbles, colorless solution.

  • Zinc + HCl
    Reaction: Zn + 2HCl → ZnCl₂ + H₂
    Bubbles, zinc disappears, colorless solution.

  • Aluminium + HCl
    Reaction: 2Al + 6HCl → 2AlCl₃ + 3H₂
    Reacts slowly at first due to oxide layer.

Reactivity Order from Acid Reactions

  • Magnesium

  • Zinc

  • Iron

  • Copper

  • Silver

  • Gold

Protective Oxide Layer of Aluminium

  • Forms aluminium oxide:
    4Al + 3O₂ → 2Al₂O₃

  • This layer protects aluminium from reacting unless removed.

Metal Displacement Reactions

Concept: A more reactive metal displaces a less reactive metal from its salt solution.

Examples:

  • Zinc + Copper(II) sulfate
    Reaction: Zn + CuSO₄ → ZnSO₄ + Cu
    Zinc is coated with copper, blue solution fades.

  • Copper + Silver nitrate
    Reaction: Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag
    Silver deposits on copper, solution turns blue.

Redox Reactions

OIL RIG: Oxidation Is Loss, Reduction Is Gain (of electrons)

Example in Displacement:

  • Zinc is oxidized: Zn → Zn²⁺ + 2e⁻

  • Copper ions are reduced: Cu²⁺ + 2e⁻ → Cu

In Acid Reactions:

  • Magnesium: Mg → Mg²⁺ + 2e⁻

  • Hydrogen ions: 2H⁺ + 2e⁻ → H₂

Key Point:
Displacement reactions and reactions with acid are redox reactions.

Reactivity Series Summary

How to Assess Reactivity:

  • Reactions with water

  • Reactions with acids

  • Displacement reactions

Reactivity Series (including Hydrogen):

  1. Potassium (K)

  2. Sodium (Na)

  3. Calcium (Ca)

  4. Magnesium (Mg)

  5. Aluminium (Al)

  6. Zinc (Zn)

  7. Iron (Fe)

  8. Hydrogen (H)

  9. Copper (Cu)

  10. Silver (Ag)

  11. Gold (Au)

Note: Carbon is also placed based on its ability to reduce metal oxides in extraction.