Chemistry - 9 - Metals

Describe the uses of metals in terms of their physical properties: Aluminium and Copper

ALUMINUM aluminium in the manufacture of aircraft because of its low density. aluminium in the manufacture of overhead electrical cables because of its low density and good electrical conductivity. Aluminium in food containers because of its resistance to corrosion COPPER copper in electrical wiring because of its good electrical conductivity and ductility

Explain the apparent unreactivity of aluminium in terms of its oxide layer

Aluminium is high in the reactivity series, but in reality, it does not react with water and the reaction with dilute acids can be quite slow. This is because it reacts readily with oxygen, forming a protective layer of aluminium oxide which is very thin. This layer prevents reaction with water and dilute acids, so aluminium can behave as if it is unreactive.

Describe an alloy a) brass b) stainless steel

An alloy as a mixture of a metal with other elements brass as a mixture of copper and zinc stainless steel as a mixture of iron and other elements such as chromium, nickel and carbon

Describe the extraction of aluminium from purified bauxite / aluminium oxide: the reactions at the electrodes, including ionic half-equations

At the cathode (negative electrode): Aluminium ions gain electrons (reduction). Al3+ + 3e- → Al At the anode (positive electrode): Oxide ions lose electrons (oxidation) 2O2- → O2 + 4e- The overall equation for the reaction is: 4Al + 3O2 → 2Al2O3 The carbon in the graphite anodes reacts with the oxygen produced to produce CO2 C(s) + O2 (g) → CO2 (g)

Explain reactivity series in-terms of their reactions

Calcium and above react with water. Metals below calcium react with steam. Metals above hydrogen react with dilute acids

State common barrier methods to prevent rusting

Coating with; Grease Paint Oil Plastic

Explain in terms of structure how alloys can be harder and stronger than the pure metals

Different sized atoms in alloys mean the layers can no longer slide over each other.

Describe the use of zinc in galvanising as an example of a barrier method and sacrificial protection

Galvanising is a process where the iron to be protected is coated with a layer of zinc Zinc is used in galvanising as zinc is more reactive than iron.

Describe the extraction of iron from hematite in the blast furnace

Iron ore (hematite), coke (an impure form of carbon), and limestone are added into the top of the blast furnace. Hot air is blown into the bottom. ZONE 1: Coke burns in the hot air forming carbon dioxide: carbon + oxygen → carbon dioxide ZONE 2: Due to high temperatures, more coke reacts with carbon dioxide forming carbon monoxide carbon + carbon dioxide → carbon monoxide ZONE 3: Carbon monoxide reduces the Iron (III) Oxide to form iron. Iron (III) oxide + carbon monoxide → Iron + carbon dioxide Limestone (calcium carbonate) is added to remove impurities from the iron ore. The limestone thermally decomposes to form calcium oxide calcium carbonate → calcium oxide + carbon dioxide The calcium oxide formed reacts with silicon dioxide, which is an impurity in the iron ore to form calcium silicate calcium oxide + silicon dioxide → calcium silicate - which floats on top of molten iron.

State that the main ore of aluminium and how is it extracted?

Main ore is bauxite Extracted by electrolysis

Describe the general chemical properties of metals, limited to their reactions with: Reactivity with Cold Water

Metals that react with cold water form a metal hydroxide and hydrogen gas metal + water → metal hydroxide + hydrogen

Describe the general chemical properties of metals, limited to their reactions with: Reactivity with Steam

Metals that react with steam form metal oxide and hydrogen gas. metal + water -> metal oxide + hydrogen

Describe the reactions, if any, of: magnesium, zinc, iron, copper, silver and gold with dilute hydrochloric acid and explain these reactions in terms of the position of the metals in the reactivity series

Only metals above hydrogen will react with dilute acids. metal + acid → salt + hydrogen Therefore: Copper, Silver and Gold will not react with acids.

State the conditions required for the rusting of iron and steel to form hydrated iron(III) oxide

Oxygen and water must be present for rust to occur. iron + water + oxygen → hydrated iron(III) oxide

Compare the general physical properties of metals and non-metals: (a) thermal conductivity (b) electrical conductivity (c) malleability and ductility (d) melting points and boiling points

Properties of metals - Forms Positive Ions - Forms Basic Oxides - Conducts Heat and Electricity - Are Malleable ( can be hammered ) - Are Ductile ( drawn into thin wires ) - High melting and Boiling Points Properties of non-metals - Forms Negative Ions - Forms Acidic Oxides - Does not conduct Heat and Electricity - Are brittle when solid - Low melting and boiling points

Describe how barrier methods prevent rusting by excluding oxygen or water

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

Describe the uses of alloys in terms of their physical properties Stainless Steel

Used in cutlery because of its hardness and resistance to corrosion

Describe the extraction of aluminium from purified bauxite / aluminium oxide: why the carbon anodes need to be regularly replaced

The carbon in the graphite anodes reacts with the oxygen produced to produce CO2 As a result the anode wears away and has to be replaced regularly.

Describe the ease in obtaining metals from their ores, related to the position of the metal in the reactivity series

Those metals placed higher up on the series (above carbon) have to be extracted using electrolysis. Metals lowerdown on the series can be extracted by heating with carbon.

Explain sacrificial protection in terms of the reactivity series and in terms of electron loss

Zinc is more reactive than iron therefore will lose its electrons more easily than iron and is oxidised more easily. The iron is less reactive therefore will not lose its electrons as easily so it is not oxidised; the zinc is sacrificed to protect the steel.

State the symbol equations for the extraction of iron from hematite

Zone 1 The burning of carbon (coke) to provide heat and produce carbon dioxide: C(s) + O2 (g) → CO2 (g) Zone 2 The reduction of carbon to carbon monoxide: C(s) + CO2 → 2CO(g) Zone 3 The reduction of iron (III) oxide by carbon monoxide: Fe2O3 (s) + 3CO(g) → 2Fe(l) + 3CO2 (g) Thermal decomposition of calcium carbonate (limestone) to calcium oxide: CaCO3 (S)→ CaO (s) + CO2 (g) The formation of slag: CaO (S) + SiO2 (s) → CaSiO3 (l)

Why alloys?

alloys can be harder and stronger than the pure metals and are more useful

Describe the extraction of aluminium from purified bauxite / aluminium oxide: Role of cryolite

aluminium oxide has a melting point of over 2000°C which would use a lot of energy and be very expensive. The resulting mixture has a lower melting point without interfering with the reaction.

Describe the general chemical properties of metals, limited to their reactions with: Reactivity with Dilute acids

metal + acid → salt + hydrogen

Describe the general chemical properties of metals, limited to their reactions with: Reactivity with oxygen

metal + oxygen → metal oxide

Describe the reactions, if any, of: potassium, sodium and calcium with cold water and explain these reactions in terms of the position of the metals in the reactivity series

metal + water → metal hydroxide + hydrogen The more reactive metals will react with cold water to form a metal hydroxide and hydrogen gas.

Describe the reactions, if any, of: magnesium with steam and explain these reactions in terms of the position of the metals in the reactivity series

metal + water → metal oxide + hydrogen Metals just below calcium in the reactivity series do not react with cold water but will react with steam to form a metal oxide and hydrogen gas