Standard Grade Chemistry 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 Elements present UsesReason Stainless steel Iron Chromium, Nickel Sinks, Cutlery Non-rusting, strong Mild steel IronCarbon Girders, Car bodies Strong, rust resistant Gold Copper Rings, Electrical contacts Good conductor, unreactive Solder Lead (50%) Tin (50%) Joining metals, electrical contacts Low melting point, good conductor BrassCopperZinc 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 Metals a) With Water Metal + Water  Metal hydroxide + Hydrogen E.g. Potassium + Water  Potassium hydroxide + Hydrogen K + H 2 O  KOH + H 2 Sodium + Water  Sodium hydroxide + Hydrogen Na + H 2 O  NaOH + H 2 Calcium + Water  Calcium hydroxide + Hydrogen Ca + H 2 O  Ca(OH) 2 + H 2 Magnesium + Water  Magnesium hydroxide + Hydrogen Mg + H 2 O  Mg(OH) 2 + H 2

Reactions of Metals b) Metal Reacting with Acid Metal + Acid  A Salt + Hydrogen E.g. Magnesium + Hydrochloric acid  Magnesium chloride + Hydrogen Mg + HCl  MgCl 2 + H 2

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 + O 2  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 HaematiteIron oxideIron BauxiteAluminium oxideAluminium GalenaLead sulphideLead CinnabarMercury sulphideMercury 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 Ag 2 O  Ag + O 2 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 Fe 2 O 3 + C  Fe + CO 2 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 + O 2  CO 2 (Zone 2) Higher up, the carbon dioxide reacts with carbon to make carbon monoxide CO 2 + C  CO

(Zone 3) Further up the carbon monoxide reacts with iron oxide to make iron and carbon dioxide Fe 2 O 3 + CO  Fe + CO 2 This is a reduction reaction.

Activity

Electrochemical Series Potassium Sodium Calcium Magnesium Aluminium Zinc Iron Nickel Tin Lead Copper Mercury Silver Gold Can be broken by heat alone Separated from ore by heating with CHARCOAL, thus releasing CARBON DIOXIDE Must be electrolysed to release metal from ore