Topic 9 Reactivity series

2.17 Order of Reactivity series

Potassoum, sodium, lithium, calcium, magnesium, aluminium, zinc, iron, tin, lead, copper, silver, gold

Mnemonic:Please Stop Learning Chemistry, My Amazing Zebra Invited Tired Lazy Cat Seeking Gold

Based on what can metals be arranged in a reactivity series?

• based on their reactions with water, dilute hydrochloric or sulfuric acid

• based on the displacement reactions between metal and metal oxides, metals and aqueous solutions of metal salts

2.15 Reactions of metal with water, dilute hydrochloric or sulfuric acid

• A few reactive metals react with water to form metal hydroxide (alkaline solution) and hydrogen gas(bubbles given off) : metal + H₂O → metal OH + H₂

• In the reactivity series, metals down to calcium react with cold water(fizzing). Magnesium reacts with steam. The rest does not react.

• Most metals react with acid to form metal salt + hydrogen gas: metal + opi acid → metal salt + H₂(can see bubbles given off)

• In the reactivity series, metals until lead react with acid.

• Almost all metals react with oxygen: metal + oxygen → metal oxide

• Metals until tin burn in oxygen. The rest (except silver and gold) tarnish.

• The only metal that does not react with any of those is gold because it is extremely unreactive.

• The relative reactivity of a metal can be deduces by checking if it reacts with water (which means it’s VERY reactive), acid (reactive), and oxygen(not so reactive).

2.16 Displacement reactions between metal and metal oxides, metals and aqueous solutions of metal salts.

A more reactive metal displaces a less reactive metal from its compound.

• Reacting a metal with another metal oxide by heating: redox reaction. The more reactive metal(the reducing agent) will be oxidised and the metal in the metal oxide will be reduced.

• Displacement reactions in salt solutions of one of the metals: The more reactive metal slowly disappears in the solution and displaces the less reactive metal.

2.18 What 2 things are needed for iron to rust? What is rust?

• oxygen

• water

Rust is a hydrated form of iron oxide

Iron + oxygen → Iron (III) oxide (which is brown)

As the oxide forms, it reacts with water to form hydrated iron oxide.

Iron oxide + water → hydrated iron oxide

• Rust is a soft solid substance that flakes off the surface of iron easily, exposing fresh iron below which then undergoes rusting

• This means that over time all of the iron rusts and its structure becomes weakened→ Rust damages the iron, results in corrosion

Investigating Iron rusting

• Nail in dry air: Rust does not form since air is dry and water is not present.

• Nail in water and air: Lots of rusting occurs since the iron is exposed to both oxygen and water

• Nail in water only: little rusting since its exposed to water and little oxygen that is dissolved in the water

• Nail in water, air and salt: the greatest amount of rusting since iron is exposed to both water and oxygen, and the salt accelerates the process(because it acts as an electrolyte, which significantly increases the conductivity of water).

• Nail in water sealed with oil: very little rusting since the oil layer prevents oxygen from dissolving into the water

• Nail in boiled water: very little rusting since boiling the water removes any dissolved oxygen

• Nail in air with calcium chloride: No rusting- calcium chloride absorbs any water molecules present due to moisture

How can the rusting of iron be prevented?

• barrier methods

• galvanising

• sacrificial protection

Barrier methods

• Rust can be prevented by coating iron with barriers that prevent the iron from coming into contact with water and oxygen

• Physical barriers include: painting, oiling/greasing, covering in plastic etc.

• However, if the coatings are washed away or scratched, the iron is once again exposed to water and oxygen and will rust.

• Moving parts of the machine cannot be painted because the pain is easily scratched, so grease is applied, which also lubricates the machinery.

Galvanising & Sacrificial protection

→ coating the iron/steel in a layer of more reativctive metal e.g. zinc. Zinc is more reactive than iron/steel so it reacts first with oxygen and water, before they reach the layer of iron underneath. This prevents the iron from rusting. This is also called sacrificial protection.

• If the coating is damaged or scratched, the iron is still protected from rusting by sacrificial protection. The more reactive metal reacts with water and oxygen preferentially, which prevents the steel from rusting.

Oxidation and Reduction

OIL RIG
Oxidation is the LOSS of electron or the GAIN of oxygen.

Reduction is the GAIN of electrons or the LOSS of oxygen.

Oxidising and reducing agent

Oxidising agent: causes another reactant to oxidise and reduces itself. (Provides the oxygen)

Reducing agent: causes another reactant to reduce and oxidises itself.(Removes the oxygen)

2.21 Practical: Reaction between HCl/H₂SO₄ and metals

in the diagram showing the reactivity series, you can see that only the more reactive metals will react with dilute acids (up to iron)

● metal + acid → hydrogen + salt

● you can observe the reaction of different metals with acids, as the most reactive will give off large amounts of H2 gas bubbles and the least reactive will not give off any at all