Metals

• Metals have many uses such as:

  Construction

  Making tin cans for food

  Making electrical wires to hang between pylons

  Making cars and other vehicles

  Making saucepans
• Aluminium 


  Density is 2.7 g/cm3

  Melting point - 659 degrees

  Strength -medium

  Electrical conductivity - good

  Reactivity - corrodes slowly

  Relative Cost - medium
• Copper


  Density - 9 g/cm3

  Melting point - 1083 degrees

  Strength - strong

  Electrical conductivity- very good

  Reactivity - corrodes slowly

  Relative Cost - medium
• Iron and Steel


  Density - 7.9 g/cm3

  Melting point - 1540 degrees

  Strength - strong

  Electrical conductivity- medium

  Reactivity - corrodes quickly

  Relative Cost - low
• Lead


  Density - 11.3 g/cm3

  Melting point - 328 degrees

  Strength - weak

  Electrical conductivity- poor for a metal

  Reactivity - corrodes slowly

  Relative Cost - low
• Tin


  Density - 7.3 g/cm3

  Melting point - 232 degrees

  Strength - weak

  Electrical conductivity- poor for a metal

  Reactivity - No corrosion

  Relative Cost - high
• Most suitable for Construction

  Copper as it is strong, corrodes slowly, it is medium cost and it has a high melting point
• Most suitable for cars and vehicles

  Aluminium as it corrodes slowly, it is light and it is medium cost
• Most suitable for electrical wires

  Copper is most suitable as it is ductile (flexible), strong and corrodes slowly
• Most suitable for coating food cans


  Lead as it is low cost, corrodes slowly and has weak conductivity
• Most suitable for aeroplanes

  Iron as it is strong, its low cost and it has a high melting point
• Properties of metals


  Lustrous - bright and shiny

  Hard and strong

  High density

  Good conductors of heat and electricity

  High melting and boiling points

  Can be bent and pressed into different shapes (malleable)

  Can be drawn into wires - ductile
• Metals 


  Metals are in left / middle of periodic table

  Non metals are in right
• The reactivity series


  When metals react with other substances the metal atoms form positive ions. The reactivity of a metal is related to its tendency to form positive ions.

  Metals can be arranged in order of their reactivity in a reactivity series
• Reactivity Series


  The metals potassium, sodium, lithium, calcium, magnesium, zinc, iron and copper can be put in order of their reactivity from their reactions with water and dilute acids

  The non metals hydrogen and carbon are often included in the reactivity series

  A more reactive metal displaces a less reactive metal from a compound
• Displacement


  The Reactivity Series of metal is a type of a chemical ‘league table’. It shows the metals in order with the most reactive at the top. Where a metal comes in the table, depends on if it reacts with oxygen, water and acid

  The reactivity series enables us to make predictions regarding chemical reactions between metals and metal salts - these are displacement reactions

  In a displacement reaction a more reactive metal displaces a less reactive metal from its compounds
• Reactions for reactivity


  Results table

  
• Magnesium


  Reacts with:

  Copper nitrate

  Iron sulphate

  Zinc sulphate

  Doesn’t react with:

  Magnesium sulphate
• Copper


  Doesn’t react with:

  Magnesium sulphate

  Copper nitrate

  Iron sulphate

  Zinc sulphate
• Iron


  Does react with:

  Copper nitrate

  Doesn’t react with:

  Magnesium sulphate

  Iron sulphate

  Zinc sulphate
• Zinc

  Does react with:

  Copper nitrate

  Iron sulphate

  Doesn’t react with

  Magnesium sulphate

  Zinc sulphate
• Metals reacting with water and acids

  The reactivity of metals with water or dilute acids is related to the tendency of the metal to form its positive ion

  The reactions of metals with acids and water is limited to room temperature and doesn’t include reactions with steam
• Ore


  A rock containing a high concentration (economically viable) of a metal or metal compound
• Native

  A metal that is found in its metallic form, either pure or as an alloy, in nature
• Extracting metals

  More reactive a metal is , the harder it is to extract the metal from its ore

  To extract the metal, you must use an element that is higher up the reactivity series

  This will kick out the metal that you want leaving you free to either sell or use it
• Extracting metals

  Unreactive metals like gold are found in the earth as metals itself but most metals are found as compounds that require chemical reactions to extract the metal

  Metals less reactive than carbon can be extracted from their oxides by reduction with carbon which involves the loss of oxygen

  Metal oxide + carbon - carbon dioxide + metal

  Oxidation is loss of electrons

  Reduction is the gain of electrons
• Displacement reaction

  A more reactive metal displaces a less reactive metal from an aqueous solution of one of its salts

  Eg: magnesium and copper sulphate - the magnesium metal forms aqueous magnesium ions and dissolves into the solution

  Magnesium + copper sulphate - copper + magnesium sulphate

  An ionic equation shows only the ions and the atoms that change in a reaction - in this reaction the sulfate ions stay the same so don’t appear in the ionic equation:

  Mg(s)+Cu2+ - Mg2+(aq)+Cu(s)

  This shows that magnesium atoms have greater tendencies to form positive ions than copper atoms
• Hydrogen in the Reactivity Series 


  These non metal can be included using displacement reactions. You can think of the metal + acid reaction as displacement of hydrogen ions, H+(aq) from solution

  Copper can’t displace the hydrogen from an acid whereas lead can - so hydrogen is placed between copper and lead
• Carbon in the reactivity Series


  Carbon can be used in the extraction of metals from their oxides (another type of displacement reaction)

  However it can only do this for metals below aluminium in the series

  It doesn’t displace aluminium from aluminium oxide as but can displace zinc from zinc oxide

  So carbon is placed between aluminium and zinc
• Oxidation and Reduction


  Can apply these definitions to displacement reactions in solutions

  The displacement of copper ions by iron - used in industry for copper extraction from copper sulphate solution, the iron in cheap scrap iron, ionic equation is:

  Fe(s)+Cu2+(aq) - Fe2+(aq)+Cu(s)

  The iron atoms lose 2 electrons to form iron ions - oxidation, half equation for this is:

  Fe(s) - Fe2+(aq)+2e-

  The 2 electrons from iron are gained by cooper atoms - reduction - copper ions reduced, half equation:

  Cu2+(aq)+2e- - Cu(s)

  Displacement reactions are also redox reactions (reduction - oxidation)
• Where do metals come from

  Found in the earth's crust

  Most metals are combined chemically with other chemical elements

  This means that the metal must be chemically separated from its compound before it can be used

  When there is enough of a metal or a metal compound in a rock to make it worth extracting, the rock is called a metal ore

  Ores are mined from the ground and some of them need to be concentrated before the metal is extracted and purified

  Eg: copper ores are ground up into a powder, them mixed with water and a chemical that makes the copper compound repel water
• Where do metals come from (2)

  Copper ores (continued) - Air is then bubbled through the mixture and the copper compounds floats on top as froth, the rocky bits sink and the concentrated copper compound is craped of the top - it is then ready to have its copper extracted.

  The worth of extracting a particular metal depends on:

  How easy it is to extract it from it's ore

  How much metal the ore contains

  The changing demands for a particular metal

  These factors can change over time ( a new cheaper method may come).
• Where do metals come from (3)

  You might also find a new way to extract a metal efficiently from a rock which contains only small amounts of a metal ore. An ore that was once thought to be 'low grade' could then become an economic source of a metal

  Metals like gold and silver are so unreactive they are found as the metals (elements) themselves - exist in native state

  Sometimes a nugget of gold is so large it can simply be picked up

  At other times, tiny flakes have to be physically separated from sand and rocks by panning
• Reduction of oxide by carbon

  The way that a metal is extracted depends on its place in the reactivity series. Carbon will displace less reactive metals from their oxides. Carbon is used to extract some metals from their ores in industry. You can find many metals such as copper, lead, iron and zinc combined with oxygen as metal oxides. Because carbon is more reactive than each of the metals, it is used to extract the metals from their oxides. Heat the metal oxide with carbon - CO2 and metal is formed

  Metal oxide and carbon - carbon dioxide and metal
• Metals and water

  Metal + water - metal hydroxide + hydrogen
• Reduction of oxide by hydrogen

  Another metal extracted by reduction of its oxide is tungsten. The non metal reacting agent is hydrogen even though carbon is cheaper. This is because carbon forms a compound tungsten carbide, with the metal formed by reduction. The tungsten from reduction of its oxide by hydrogen is very pure.

  Tungsten oxide and hydrogen - tungsten and water (as steam)

  WO3(s)+3H2(g) - W(s)+3H20(g)

  The metals that are more reactive than carbon aren't extracted from their ores by reduction with carbon - instead they are extracted by electrolysis of the molten metal compound.
• Extracting copper from copper rich ores


  Most copper is extracted from this - finite resource, in danger of running out

  2 main methods:

  1 - Sulfric acid is used to produce copper sulfate solution, before extracting the copper metal

  2 - Smelting (roasting) - copper ore is heated to a high temp in a furnace with air to produce impure copper, that is then used as the positive electrode in electrolysis to make pure copper

  80% of copper is produced by smelting

  Smelting and purifying copper ores use lots of energy and electricity which means a lot of money and pollution of the environment.
• Extracting copper from copper rich ores

  Metal ions are positively charged meaning in electrolysis they deposit at the cathode. In industry the use of electrolysis of copper is made in many cells at the same time - gives pure copper for electrical wiring. Electrolysis used to purify impure copper from smelting.

  Cathode: Cu2+(aq)+2e- - Cu(s)

  Anode: Cu(s) - Cu2+(aq)+2e-

  The copper can be extracted from copper sulphate solution in industry by adding scrap iron - iron can displace copper from its solution

  Iron + copper sulphate - Iron sulphate + copper

  Fe(s)+Cu2+(aq) - Fe2+(aq)+Cu(s)
• Extracting copper from low grade ores

  Would be uneconomical using traditional methods - new techniques use bacteria (bioleaching) or plants (phytomining) to help extract copper.
• Phytomining

  Plants that can absorb copper ions are grown on soil containing low grade copper ore. This could be on heaps of previously discarded waste from the processing of copper rich ores. Then the plants are burned and copper is extracted from copper compounds in the ash. The copper ions can be dissolved from the ash by adding sulfric acid - this makes a solution (leachate) of copper sulphate. Displacement by scrap iron and then electrolysis makes pure copper metal.