Metals and Reactivity Notes

Metals and Reactivity

Physical Properties of Metals

  • Metals possess physical properties.

  • Bronze, an alloy of tin and copper, exhibits greater hardness compared to its constituent metals.

Chemical Properties and Reactivity Series

  • Metals also have chemical properties.

  • By observing the reactions of metals with common substances, a reactivity series can be established.

Demo A: Reactions of Metals with Oxygen

  • Observations of metals heated in air:

    • Magnesium (Mg)

    • Copper (Cu)

    • Iron (Fe)

  • Order of increasing reactivity (based on observations):

    • Most Reactive

    • Least Reactive

  • General word equation for the reaction of a metal with oxygen:

    • Metal + Oxygen → Metal Oxide

Demo B: Reactions of Metals with Water

  • Observations of metals reacting with water:

    • Sodium (Na)

    • Potassium (K)

    • Lithium (Li)

    • Magnesium (Mg)

    • Calcium (Ca)

  • Order of increasing reactivity (based on observations):

    • Most Reactive

    • Least Reactive

  • General word equation for the reaction of a metal with water:

    • Metal + Water → Metal Hydroxide + Hydrogen

  • Balanced symbol equation for the reaction of sodium with water:

    • 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)

Reaction of Magnesium with Steam

  • Some metals react slowly with cold water but can react with steam.

  • Experiment diagram for the reaction of magnesium with steam.

  • Observation: Magnesium reacts with steam.

  • Word equation for the reaction of magnesium with steam:

    • Magnesium + Steam → Magnesium Oxide + Hydrogen

  • Balanced symbol equation for the reaction of magnesium with steam:

    • Mg(s) + H2O(g) → MgO(s) + H2(g)

Metals with Dilute Acids

  • Demonstration of the reaction of magnesium with dilute sulfuric acid.

  • Experiment diagram showing gas collection.

  • Observations:

    • Gas given off.

    • The metal reacts.

  • The gas given off is hydrogen.

  • General word equation for the reaction of a metal with dilute acid:

    • Metal + Dilute Acid → Salt + Hydrogen

This reaction is an important demonstration of the reactivity series, showing that more reactive metals will produce hydrogen more vigorously when treated with acids.

Oxidation and Reduction

  • Oxidation: Addition of oxygen.

  • Reduction: Loss of oxygen.

  • Example:

    • 2 PbO + C → CO_2 + 2 Pb

    • Carbon is oxidised, and lead oxide is reduced.

  • Questions:

    1. Copper oxide + carbon → copper + carbon dioxide

    2. Iron oxide + carbon monoxide → iron + carbon dioxide

    3. Magnesium + lead oxide → magnesium oxide + lead

    4. Carbon dioxide + carbon → carbon monoxide

    5. Aluminium + water → aluminium oxide + hydrogen

  • Reducing agent: The substance that gains oxygen (gets oxidised).

  • Oxidising agent: The substance that loses oxygen (gets reduced).

  • Alternative definition:

    • Oxidation: Loss of electrons.

    • Reduction: Gain of electrons.

Displacement Reactions

  • A metal higher in the reactivity series will displace a metal lower down from a solution of its salt.

  • Displacement reaction indicators: change of color on the metal surface and/or temperature change.

  • Record results and write word equations for the following demonstrations:

    • Iron and Copper Sulfate

    • Zinc and Lead Nitrate

    • Copper and Silver Nitrate

Analysis of Displacement Reactions

  • Place zinc, magnesium, copper, and iron in order of reactivity based on tests and observations.

    • Most Reactive

    • Least Reactive

  • Relationship between position in the reactivity series and temperature difference when the metal reacts with solutions of other metal salts.

  • Write word equations for three displacement reactions observed in the practical.

Metal Reactivity Series Summary

  • Metals are ordered by chemical reactivity (most to least reactive).

    • Potassium, Sodium, Calcium, Magnesium, Aluminium, Carbon, Zinc, Iron, Lead, Hydrogen, Copper, Silver, Gold

    • Please Stop Calling Me A Careless Zebra Instead Learn How Copper Saves Gold

  • Aluminium often appears less reactive due to a protective layer of aluminium oxide.

  • Hydrogen is included in the series.

  • Metals above hydrogen displace hydrogen from acids.

  • Metals below hydrogen do not react with these acids.

Rusting and Corrosion

  • Discuss the differences between corrosion and rusting, including the chemical name and formula for rust.

  • Corrosion: Many metals corrode.

  • Rusting: Corrosion of iron.

  • Rust is made of hydrated iron(III) oxide (Fe2O3 ")]

Factors Affecting the Speed of Rusting

  • Factors are investigated in test tube reactions.

  • Deduce the three factors that govern the speed at which iron rusts:

    1. Oxygen

    2. Water

    3. Electrolyte (e.g. salt)

  • Experiment setups:

    • Oxygenated water (shaken): Rust

    • Humid air: Rust

    • Dry air (anhydrous CaCl_2): No rust

    • Deoxygenated water (boiled water/oil layer): No rust

    • Salt water: Extensive rust

  • Purpose of CaCl_2$$ in experiment 3: To absorb moisture and maintain dry air.

  • Purpose of the oil layer in experiment 4: To prevent oxygen from dissolving in the water.

Preventing Rusting

  • Discuss methods to prevent rusting and provide examples.

  • Major methods to prevent rusting:

    1. Barrier methods (e.g., painting, coating with plastic)

    2. Sacrificial protection (e.g., galvanisation)

    3. Applying a protective layer (e.g. oil)

Galvanisation

  • Galvanising: Coating iron or steel with a thin layer of zinc.

  • Stops oxygen and water from reaching the metal.

  • Zinc acts as a sacrificial metal, oxidising before iron.

  • Common method: Hot-dip galvanising.

Sacrificial Protection

  • A more reactive metal (e.g., zinc or magnesium) is attached to the iron structure.

  • The reactive metal corrodes in preference to iron.

  • Examples: Ships, oil rigs, underground pipelines.

  • Corrosion experiment example: Iron nail with silver wire is slightly rusty; iron nail with zinc wire is not rusty; and iron nail with copper wire is very rusty.