Standard GradeChemistry

Topic 11 - Metals

Properties of Metals Density – this is the mass of a substance in a given

volume. A high density material is much heavier than the same volume of

a low density material e.g. aluminium (low density) – used to build aircraft. Lead (high density) – is used as weights for fishing nets/lines.

Thermal Conductivity - metals all conduct heat well because of the close contact of the atoms. E.g. pots/pans.

Electrical Conductivity - metals all conduct electricity when solid and when molten because electrons can travel easily through the structure. E.g. cables

Malleability - metals can be beaten into different shapes. E.g. jewellery.

Strength - most metals are strong because of the metallic bond which holds the atoms together. E.g. bridges, cars, buildings etc.

Alloys

The properties of metals can be extended or altered by mixing them with other metals or with non-metals.

Iron can be changed into stainless steel by mixing it with small amounts of chromium. This stops the metal rusting.

Alloy Main

Metal

Other Element

s present

Uses Reason

Stainless steel

Iron Chromiu

m, Nickel Sinks, Cutlery

Non-rusting, strong

Mild steel

Iron Carbon Girders, Car

bodies Strong, rust resistant

Gold Gold Copper Rings, Electrical

contacts Good conductor,

unreactive

Solder Lead

(50%) Tin (50%)

Joining metals, electrical contacts

Low melting point, good conductor

Brass Coppe

r Zinc

Machine bearings,

ornaments

Hard wearing, attractive

Recycling Metals

Metals need to be recycled because they will not last forever (they are finite resources).

Reactions of Metalsa) With Water

Metal + Water Metal hydroxide + Hydrogen

E.g.Potassium + Water Potassium hydroxide + Hydrogen

K + H2O KOH + H2  

Sodium + Water Sodium hydroxide + Hydrogen

Na + H2O NaOH + H2  

Calcium + Water Calcium hydroxide + Hydrogen

Ca + H2O Ca(OH)2 + H2  

Magnesium + Water Magnesium hydroxide + Hydrogen

Mg + H2O Mg(OH)2 + H2

Reactions of Metalsb) Metal Reacting with Acid

Metal + Acid A Salt + Hydrogen 

E.g.Magnesium + Hydrochloric acid Magnesium chloride +

Hydrogen

Mg + HCl MgCl2 + H2

Reactions of Metals c) Metals reacting with oxygen

Oxygen can be made by heating potassium permanganate in a test tube and allowing the gas to pass through the preheated metal.

Metal + Oxygen Metal oxide E.g.

Magnesium + Oxygen Magnesium oxide

Mg + O2 MgO

Summary

Metal Ores

Ores are naturally-occuring compounds of metals from which metals can be extracted.

The three main types of ore are metal carbonates, metal oxide and metal sulphides.

Common Ores

Common name

Chemical name Metal

present

Haematite Iron oxide Iron

Bauxite Aluminium oxide Aluminium

Galena Lead sulphide Lead

Cinnabar Mercury sulphide Mercury

Malachite Copper(II) carbonate

Copper

Extracting Metals

Metals such as gold and silver occur uncombined on earth because they are unreactive and because of this these elements were among the first to be discovered.

Other metals, such as those in the table are found in compounds and have to be extracted (which is an example of reduction).

Extraction of Metals from Ores

The method used to extract a metal depends on the reactivity of the metal.

The more reactive the metal, the more difficult it is to extract.

The less reactive the metal, the easier it is to extract.

Methods of extraction a) Heating metal oxides

Silver oxide Silver + Oxygen

Ag2O Ag + O2

Few metals can be obtained in this way.

b) Heating Metal Oxides with Carbon

Metal oxide + Carbon Metal + Carbon dioxide  

E.g. Iron oxide + Carbon Iron + Carbon dioxide

Fe2O3 + C Fe + CO2

This method is used to extract metals below aluminium in the reactivity series.

c) Using Electricity

Electricity can be used to split ionic compounds into their elements in a process called electrolysis.

The method is used to extract reactive metals above zinc in the reactivity series.

A large electric current is passed through the molten compound, and metal appears at the negative electrode.

d) Heating with Carbon Monoxide

Iron is extracted from its ore in the blast furnace by heating with carbon (coke) in the presence of air.

(Zone 1)

At the bottom of the furnace the reaction makes carbon dioxide

C + O2 CO2

(Zone 2)

Higher up, the carbon dioxide reacts with carbon to make carbon monoxide

CO2 + C CO

(Zone 3) Further up the carbon monoxide reacts with iron oxide to make iron and carbon dioxide

Fe2O3 + CO Fe + CO2

This is a reduction reaction.

Activity

Electrochemical Series

Potassium

Sodium

Calcium

Magnesium

Aluminium

Zinc

Iron

Nickel

Tin

Lead

Copper

Mercury

Silver

GoldCan be broken by heat alone

Separated from ore by heating with

CHARCOAL, thus releasing CARBON

DIOXIDE

Must be electrolysed to release

metal from ore