Metal

The composition of earth crust

1. Oxygen and silicon make up nearly three-quarters of the crust. They occur as compound form such as silicon dioxide and iron(III) oxide.

2. The rest of the metals such as alluminium and potassium made up over one-quarter of the crust. 3. All the other metals made up less than 2% of the earth crust such as gold, silver and platinum

that is why they are so expensive due to scarcity. 4. Examples of metal ore:

i. Rock salt: mostly sodium chlorideii. Bauxite: aluminium oxideiii. Gold (occurs native)

5. Questions will be asked by the companies before proceeding in mining.

Extraction

Metal Method of extractionPotassiumSodium More powerful

Calcium Metals more reactive

Ore more diff electrolysis

Magnesium to decompose More expensiveAluminiumCarbonZinc Heating with reducing Iron agent- carbon / COLeadSilver Occurs native

GoldOre extraction

1. 3 examples of ore extraction area. Iron ore: reduction of iron(III) oxides

Fe2O3 + 3CO 2Fe + 3CO2

b. Aluminium ore: reduction of aluminium oxide.2Al2O3 4Al + 3O2

c. Zinc blende: mainly zinc sulfide.

Zinc Sulfide

1. Firstly, ZnS is roasted in air giving zinc oxide and sulfur dioxide2ZnS + 3O2 2ZnO + 2SO2

2. Then, the oxide is reduced by either ways:i. Using carbon monoxideii. Using electrolysis

3. Using carbon monoxide ( furnace )i. ZnO + CO Zn + CO2

ii. Final mixture contain zinc and impurities, separated by fractional distillation ( 907 degree )

4. Using electrolysis: (gives high purity zinc)i. The compound is dissolved in dilute sulfuric acid (made from the SO2) as the compound

has high melting point and zinc oxide is insoluble in water.ii. Zinc oxide become the base neutralizes the sulfuric acid producing zinc sulfate

(electrolyte)iii. Undergoes electrolysis, and zinc is deposited at the cathode:

Zn2+ + 2e- Zniv. Scraped off the cathode and melted into bar to sell.

The blast furnace (30 metres)

Process

1. A mixture (charge), containing iron ore is added through the top of the furnace.2. Hot air blasted through the bottom.3. After a series of reaction, liquid iron collected at the bottom.4. Charge: contain Iron ore (Fe2O3), Limestone (CaCO3) and Coke (pure carbon).

Reaction

Reactions RemarksStage 1: The coke burns, giving off heatThe blast of hot air start the coke burning.It reacts with the oxygen in the air, giving out carbon dioxide.C(s) + O2(g) CO2(g)

- Redox reaction- Carbon is oxidized- Exothermic

Stage 2: Carbon monoxide is madeThe carbon dioxide reacts with more cokeC(s) + CO2(g) 2CO(g)

- Carbon dioxide is reduced- Endothermic

Stage 3: The iron(III) oxide is reducedCarbon monoxide reacts with the iron ore, giving liquid iron:Fe2O3(s) + 3CO(g) – 2Fe (l) + 3CO2(g)

- Carbon monoxide act as reducing agent,- CO is oxidizes to CO2

LimestoneLimestone breaks down in the heat:CaCO3 CaO(s) + CO2(g)Calcium oxide form reacts with the sandCaO(s) + SiO2(s) CaSO3(s)Calcium silicate forms a slag which runs down the furnace and floats on the iron.

- Purpose: produce CaO to remove the sand

- Calcium silicate is used for road building

The waste gases: hot CO2 and N come out from the top of the furnace. The heat is removed from them to heat the incoming blast of air

- CO2 is from reaction 3- N is from the air blast.

1. The iron from the blast furnace is known as pig iron. It is impure which contain mostly sand and carbon.

2. These iron are used to make cast iron(hard but brittle-due to high percentage of carbon). Eg, canister

3. Most of the iron are used to make steel.

Aluminium Extraction

1. Geologist will analyze the rock on how many bauxite it is.2. The bauxite is red-brown in colour, the ore is taken to a bauxite plant where impurities is

removed resulting white aluminium oxide or alumina.3. The alumina is taken to another plant or another country for electrolysis.4. The extracted metal is made into sheets and blocks.

The electrolysis

1. Alumina is dissolved in molten cryolite, or sodium aluminium fluoride which has a lowe melting point.

2. Once alumina is dissolves, its aluminium and oxide ions are free to move.3. Cathode: The aluminium ions gain electrons:

4Al3+(l) + 12e- 4Al (l)4. The aluminium drop to the bottom as molten metal.5. Anode: The oxygen ions lose electrons:

6O- (l) 3O2(g) + 12e- The oxygen gas, then react with the anode:C(s) + O2(g) CO2 (g) So the carbon block corrode and need to be replaced.

6. The overall reaction:2Al2O3(l) 4Al (l) + 3O2(g)

Summary of the properties and uses of each metals.

Metals Uses PropertiesAluminium Overhead electricity cable (with

a steel core for strength)- Good conductor of

electricity - Cheaper and lighter

compare to copper- Ductile- Resist to corrosion

Cooking foil and food cartons - Non toxic- Resistant to corrosion- Can be rolled to thin

sheetDrink cans - Light

- Non toxic- Resistant to corrosion

Coating CDs and DVDs - Can be deposited as a thin film

- Shiny surface reflects laser beam

Copper Electrical wiring - Good conductor of electricity

- DuctileSaucepans and its base - Malleable

- Conduct heat- Unreactive- Tough

Zinc Protecting steel from rusting - Offer sacrificial protection to the iron in steel

Coating and galvanishing iron and steel

- Resists corrosion but offer sacrificial protection if coating cracks

For torch batteries - Gives current when connected.

Alloy

1. Alloy: Mixture of metal and other substance. (eg: brass: molten zinc + copper)2. Properties:

- Pure metal- Arranged in a regular

lattice

- When pressure is applied, the layers can slide over each other easily. That is why metal are malleable and ductile.

- When metal turn to alloy, new atoms enter the lattice

- Can no longer slide easily- That is why alloy is

stronger than metal3. Besides stronger, alloy is also more resistant to corrosion.4. Examples of alloy:

Alloy Made from Special properties UsesBrass 70% Copper

30% zincHarder than copper, does not corrode

Musical instrument, ornament, door knobs

Aluminium alloy 90.25% Aluminium6% zinc2.5% magnesium1.25% copper

Light but strong Doesn’t corrode

Aircraft

Mild steel 99.7% iron0.3% carbon

Harder and stronger Building ships, car bodies and machinery

Stainless steel 70% iron20% chromium 10% nickel

HarderRust proof

Cutlery and equipment in chemical factories.

Making steel

1. Steel is made from the molten iron from the blast furnace which is impure.2. Firstly, the impurities is removed from the iron:- The molten iron is poured into an oxygen furnace, a jet of oxygen is turn on.- The oxygen reacts with the carbon, forming carbon monoxide and carbon dioxide gases which is

carried out. The oxygen also react with other impurities to form acidic oxides.- Then calcium oxide is added to react with silicon dioxide and other acidic oxides to give a slag

and skimmed off.3. Some steel are just iron plus carbon because it makes them stronger. However too much

carbon will cause the iron brittle and hard to shape. Therefore, carbon content is checked continuously.

4. Secondly, other elements may be added

- Material are measure carefully go give steel such as stainless steel.