d - Reactivity series (copy)

2d (2.15-2.21)

Metal reactions with acid

Metal reactions with acid

Acid + Metal → Salt + Hydrogen

Can use reactions of different metals with dilute acids to see how reactive they are
The more reactive the metal, the faster the reaction

Investigating metal reactions with acid

• Set up 3 boiling tubes + fill them with equal volumes of dilute hydrochloric/sulfuric acid

• Place pieces of magnesium, zinc, iron in separate tubes - make sure size + shape of pieces is same

• Speed of reaction is indicated by the rate that hydrogen bubbles are given off

• Hydrogen is confirmed by burning split test - magnesium should give loudest ‘squeaky pop’ because it’s the most vigorous, producing the most hydrogen gas

Metal reactions with water

metal + water → metal hydroxide + hydrogen

• Very reactive metals like potassium, sodium, lithium, calcium react vigorously with water

• More reactive metal = more energy given out by reaction
  Reaction with potassium gives enough energy to ignite hydrogen

• Less reactive metals (magnesium, zinc, iron) won’t react much with cold water, but react with steam

• Copper doesn’t react with water/steam

Metal/metal oxide displacement reactions

• More reactive metal displaces less reactive metal from its oxide

  → because it bonds more strongly to oxygen

• These are redox reactions - metal is oxidised and displaced metal ion is reduced

Metal salts displacement reactions

• Metal compounds like copper sulfate are metal salts

• If you put reactive metal into solution of less reactive metal salt, reactive metal replaces less reactive metal in salt

Metal reactivity series

Rusting

• Iron corrodes easily (rusts)

• Conditions: in contact with oxygen (from air) and water

• Oxidation reaction occurs - iron gains oxygen to form iron(III) oxide

• Water becomes loosely bonded to iron(III) oxide, resulting in hydrated iron(III) oxide - called rust

iron + oxygen + water → hydrated iron(III) oxide

Barrier method

To prevent rusting

• Painting/coating with plastic - ideal for big + small structures
  Can be decorative

• Oiling/greasing - has to be used when moving parts are involved, like on bike chains

Sacrificial method

To prevent rusting

• Zinc often used as sacrificial metal

• Zinc is more reactive than iron

• → zinc is oxidised instead of iron

• Coating of zinc can be sprayed on object - galvanising

• Or big blocks of zinc can be bolted to iron
  Used on ships’ hulls

Oxidation

Addition of oxygen

Loss of electrons
(OIL - Oxidisation Is Loss)

Reduction

Removal of oxygen

Gain of electrons
(RIG - Reduction Is Gain)

Redox

Reactions where both oxidisation and reduction occur

Oxidising agent

Substance that oxidises metal

Is itself reduced in reaction

Reducing agent

Substance that reduces metal

Is itself oxidised in reaction