Reactivity Series

Reaction with Water ~ Hydrochloric or Sulfuric Acid:

- Potassium: Lilac flame, vigorous effervescence, floats and rapidly moves on the water's surface, melts into a ball → water → acid.
- Too dangerous to react, ∴ it is very reactive → acid.

- Sodium: Medium effervescence, melts into a ball, eventually disappears, floats + rushes on the surface → water → acid.
- Too dangerous to react, ∴ it is very reactive → acid.

- Lithium: Slower effervescence, floats on the surface, moves slower, disappears, reacts readily → water → acid.
- Too dangerous to react, ∴ it is very reactive → acid.

- Calcium: Sinks, effervescence → water
- Too dangerous to react, ∴ it is very reactive → acid.

- Aluminium: There is no reaction → water.
- No reaction at first; bubbles are produced (effervescence) rapidly after a certain amount of time → water → acid.

- Magnesium: Slow reaction → water.
- The acid is characterised by effervescence, steam, melting, floating, and moving rapidly on the surface.

- Zinc: Sinks to bottom, lots of effervescence → acid.
- No reaction → water.

- Iron: Sinks to bottom, slow reaction, a few bubbles → acid.
- No reaction → water.

- Others: Copper, silver, and gold are unreactive with water + acid.

- Metal + Water → Metal hydroxide + Hydrogen

Order of Reactivity:

- Potassium - Very reactive
- Sodium - Very reactive
- Lithium - Very reactive
- Calcium - Very reactive
- Magnesium - Fairly reactive
- Aluminium - Fairly reactive
- Carbon - Fairly reactive
- Zinc - Fairly reactive
- Iron - Not very reactive
- Hydrogen - Not very reactive
- Copper - Not very reactive
- Silver - Not very reactive
- Gold - Not at all reactive

Metals and Acids

Acid	Formula	Type of salt made	Formula of ion
Hydrochloric acid	HCl	Chloride	Cl^-
Sulfuric acid	H₂SO₄	Sulfate	SO₄^2-
Nitric acid	HNO₃	Nitrate	NO₃^-

- When a metal reacts with an acid, it makes a salt + hydrogen.
- Metal + Acid → Salt + Hydrogen

Examples:

1. Mg + 2HCl → MgCl₂ + H₂
2. Al + HNO₃ → AlNO₃ + H₂
3. 2Al + 6HNO₃ → 2Al(NO₃)₃ + 3H₂

Examples:

Lithium + Hydrochloric acid → Lithium chloride + Hydrogen
→ 2Li(s) + 2HCl(aq) → 2LiCl(aq) + H₂(g)
H⁺(aq) + 2Cl^-(aq) → 2Li⁺(aq) + 2Cl^-(aq) + H₂(g)
→ Lithium is oxidised (redox reaction).
→ Hydrogen is reduced (redox reaction).

Metal Displacement Reactions

Displacement reaction: When a more reactive metal displaces a less reactive metal from its compound.

Metals and Metal Oxides:

- Reacting Mg(s) with CuO(s)

Observations:

- Bright white light and a big explosion.
- A white solid is formed.

Equation:

- Mg(s) + CuO(s) → Cu(s) + MgO(s) white powder
→ This is a redox reaction. Mg undergoes oxidation, while CuO undergoes reduction.
→ CuO is the oxidising agent, and Mg is the reducing agent.

Examples: (unbalanced)

- MgO + Na → Na₂O + Mg
- ZnO + Fe → no reaction ∴ Zn is more reactive than Fe.

Metals and their Compounds in aq:

- When a metal dissolves into a solution, it displaces a less reactive metal in the compound.
- E.g., copper + silver nitrate solution → silver + copper nitrate solution.

	Magnecium nitrate solution	Copper (II) sulfate solution	Zinc sulfate solution	Iron (III) chloride solution
Magnesium	×	Fastest reaction, Mg turns darker (Red)	Vigorous effervescence, Mg turns a darker green.	Vigorous effervescence
Copper	No reaction	×	No reaction	No reaction
Zinc	No reaction	Fast reaction, Zn turns a darker colour.	×	Moderate effervescence
Iron	No reaction	Slow reaction, Fe copper colour.	No reaction	×

- X = Metal cannot displace itself.
- Most vigorous reaction in column (b) when the difference in reactivity between metal + metal observed was furthest away.

- Order of reactivity ∴ → Mg, Zn, Fe, Cu.

- Mg(s) + ZnSO₄(aq) → Zn(s) + MgSO₄(aq)
- Mg(s) + Zn²⁺(aq) → Mg²⁺(aq) + Zn(s)

- 3Zn + 2FeCl₃ → 3ZnCI₂ + 2Fe
- 3Zn (s) + 2Fe³⁺(aq) → 3Zn²⁺(aq) + 2Fe(s)

Metals in Competition With Carbon

1. Fill half of a 250 cm³ beaker with water.

2. Heat an ignition tube containing a mixture of copper (II) oxide + charcoal (carbon) in a strong Bunsen burner flame at 45° for a few minutes until it glows red.
- Make sure the test tube isn't pointing at anyone. If the liquid starts to move up the tube, gently tap the tube's base on the heatproof mat.

3. When the ignition tube is at its hottest, a despite-heap spreads through the mixture and is plunged straight into a beaker of water.
- The tube may break.

4. Let contents of ignition tube settle + decant mixture at bottom of beaker → Red/brown colour
Copper (II) oxide + Carbon → Carbon dioxide + Copper

- CuO is reduced (loses O₂) + C is oxidised (gains O₂)
- C is above Cu in the reactivity series.

2. Aluminium oxide + Carbon → No reaction

Rusting of Iron

- Rusting is the corrosion of steel (which contains iron). It's an oxidation process.
- Other metals can corrode but not rust.
- Rust is hydrated iron (III) oxide: Red/Brown
- Oxygen + water is essential for rusting to occur.
- 4Fe + 3O₂ + xH₂O → 2Fe₂O₃ x H₂O
- Rust is a soft, crumbly solid that flakes off to leave more iron available to rust again.
- Iron objects rust more rapidly in seaside areas ∴ there is salty water in the air. There is no oxygen in boiled water.

Prevention of Rusting:

Barrier Methods:
- Painting: Used to prevent rusting in ships, vehicles, and bridges; the paint covers the iron (steel). However, if paint is scratched, rusting starts and can be decorative.

- Oiling/Greasing: Parts of machines that move are unable to be protected from rusting by paint, as they would get scratched off. Instead they're oiled/greased, which helps lubricate moving parts and stops them from being eroded.

- Covering with plastic: Steel is sometimes coated with plastic in items like garden chairs, towel rails, food cans, and dish racks. This plastic is inexpensive and occasionally coloured to enhance its aesthetic appeal.

Galvanising:
- Thin zinc can be used to coat some steel objects like patios and bins. ∴ Taps are often coated with Cr; however, Cr is only a bit more reactive than Fe, so O₂ in the air will react with it. Zn is more reactive than Fe, so protection is worse. Using Cr is not only more expensive, but also more appealing.

Sacrificial protection:
- Protects iron from rusting. For example, one can attach blocks of Zn to the steel hulls of ships. Zn is more reactive than Fe; it corrodes. Zn blocks undergo replacement once they fully corrode. Underground pipelines also employ this protection method. This protection method involves placing Zn blocks with sacks of magnesium at intervals along the pipe. Ship hulls can also utilise this method.

Alloys:

- The regular structure of pure metals makes them soft, often too soft for use in everyday life.
- Alloys are made by adding other elements to the metal.
- Different elements have different-sized atoms, so when a different element is added with a pure metal, the new atoms will distort the layers of metal atoms, making it more difficult for them to slide over each other.
→ Alloys are harder than pure metals.

Steel:

- Alloys of iron, or steel, are often used instead of pure iron.
- Steels are made by adding small amounts of carbon + sometimes other metals to carbon.

- Everyday life uses many other alloys.
→ e.g., brass (Cu + Zn) and bronze (Cu + Sn)

Metal Ores:

- Metals that are unreactive don't tend to form compounds with other elements, e.g., gold is found uncombined, you find them and dig them up. Native means an element exists on its own.
- Most metals do react with other elements to form compounds found naturally in the Earth's crust.
- Metal ore = A rock that contains enough mineral (metal) to make it worthwhile extracting.
→ There are limited amounts of metal ores, and they are finite resources.
- The more reactive a metal is, the harder it is to extract it from a compound.

Methods of Extraction:

- The process of electrolysis extracts the following metals:
K, Na, Ca, Mg, Al, and C.
- They are very expensive. It uses lots of energy and electricity.
- Only metals that are less reactive than carbon can be extracted using a reduction reaction with carbon. This is done by heating the ore with carbon monoxide or carbon.
→ For instance, a blast furnace reduces iron oxide to produce iron.
→ Fe₂O3 + 3C → 4Fe + 3CO₂

- The metals that are extracted by reduction using carbon:
Zn, Fe, Sn, Cu
- Here, carbon is the reducing agent that separates oxygen from iron.
- Carbon can only take the oxygen away from elements less reactive than itself.

The following metals exist as uncombined elements:
Ag and Au.
- More reactive elements come from compounds more readily, meaning their ores are very stable.
→ Electrolysis is used to separate metal.

- Metal ores are composed of metal oxides, but many also contain compounds like sulfides which can be converted into oxides.
- e.g., 2ZnS + 3O₂ → 2ZnO + 2SO₂, then O₂ needs to be removed:
- 2ZnO + C → 2Zn + CO₂

Uses of Metals:

Iron, Aluminium, and Copper:

- All dense and lustrous (shiny) and have high m.p./b.p.
- High tensile strength = strong and hard to break
- Malleable and good conductors.

Iron:

- Adding other materials to iron can change its properties.
- Wrought iron is completely pure iron; it's malleable, so it's used to make gates and railings.
- The main issue is that it rusts easily.

Aluminium:

- Doesn't corrode easily (unlike iron) → useful for products that come in contact with water/the air, e.g., drink cans.
- Aluminium reacts very quickly with oxygen in the air to form aluminium oxide. A nice, protective layer of this sticks firmly to the aluminium below and stops any further reaction from taking place.
- Aluminium is much less dense than iron → lighter weight → useful when the weight of metal is important, e.g., for the blueest aeroplanes.

Copper:

- Good conductor of heat and electricity.
→ Used in electrical components and wiring as it has low resistance and efficiently transfers electricity.
→ Also used in heating systems, e.g., underfloor heating, as it allows quick transfer of heat to surroundings.