How are metals extracted from their ores? How are metals prevented from reverting to their oxides?

1. How are metals extracted from their ores? How are metals prevented from reverting to their oxides? Reactivity series Electrolysis background How to extract metals IRON Preventing iron reverting BRINGS YOU BACK HERE ALUMINIUM Preventing aluminium reverting END Copper purification

2. Some metals are more reactive than others. A list of metals in order of their reactivity is called the REACTIVITY SERIES. HIGH REACTIVITY copper oxide copper + oxygen    2 2 2 2 balanced balanced The metal burns with a bright, white flame, leaving a white ash – magnesium oxide. The metal slowly gets a black covering of copper oxide when heated. All these metals burn vigorously with a bright flame. An unreactive element, found in the earth’s crust as the metal itself. Little reaction with oxygen. LOW REACTIVITY Reactions with air / oxygen Potassium (K) Sodium (Na) Calcium (Ca) Magnesium (Mg) Aluminium (Al) Zinc (Zn) Iron (Fe) Tin (Sn) Lead (Pb) Copper (Cu) Silver (Ag) Gold (Au) Platinum (Pt) Cu + O2 CuO 2 NOT balanced The burning of magnesium ….. Mg + O2 MgO

3. SUMMARY OF REACTIONS WITH WATER • The less reactive metals do nothing. • Magnesium reacts only when heated with steam. • Calcium reacts gently when cold • Sodium & potassium react increasingly violently when cold. • IT ALL FITS IN WITH THE REACTIVITY SERIES Calcium slowly dissolves in cold water and fizzes. The solution is an ALKALI The gas is hydrogen. The hot metal burns with a bright, white flame when steamis passed over it. It produces magnesium oxide. Hydrogen can be detected.. Sodium and potassium run around on the surface of cold water, produce heat & dissolve, with lots of fizzing. The solution is a strong ALKALI The gas is hydrogen.    No reactions. balanced balanced balanced magnesium oxide (s) magnesium (s) + water (g)  + hydrogen(g) calcium hydroxide(aq) calcium(s) + water(l)  + hydrogen(g) Reactions of metals with water This state symbol, (g) for “gas” tells us it’s STEAM liquid water alkalis contain the hydroxide ion, OH- HIGH REACTIVITY Potassium (K) Sodium (Na) Calcium (Ca) Magnesium (Mg) Aluminium (Al) Zinc (Zn) Iron (Fe) Lead (Pb) Copper (Cu) Gold (Au) sodium (s) + water (l)  sodium hydroxide(aq) + hydrogen(g) 2 Na + H2O  NaOH + H2 Mg + H2O  MgO + H2 2 2 Note: metals that react with STEAM produce the OXIDE metals that react with WATER produce the HYDROXIDE Ca + H2O  Ca(OH)2 + H2 2 NOT balanced NOT balanced

4. The zinc displaces the copper and forces the copper to become an element.  NOTE : Lead, for example would not displace iron from iron chloride solution because lead is LESS reactive. x balanced Pb(s) + FeCl3 (aq) copper displaced from its compound zinc is more reactive & becomes a compound A MORE REACTIVE METAL CAN DISPLACE A LESS REACTIVE ONE FROM ITS COMPOUNDS MORE REACTIVE Sodium (Na) Calcium (Ca) Magnesium (Mg) Aluminium (Al) Zinc (Zn) Iron (Fe) Lead (Pb) Copper (Cu) Gold (Au) Put some zinc metal into blue copper sulphate solution. Because zinc is more reactive, it has a greater tendency to become a compound than copper has. LESS REACTIVE Zinc(s) + copper sulphate(aq)  zinc sulphate(aq) + copper(s) In the test tube we see the zinc dissolving, the copper sulphate solution getting less blue and copper metal appearing at the bottom. CuSO4  Zn + ZnSO4 + Cu REMEMBER The MORE reactive a metal is, the more it likes being in a COMPOUND The LESS reactive a metal is, the more it likes being an ELEMENT The zinc has displaced the copper from its compound.

5. x  Cu(s) + ZnO (s)  balanced Aluminium oxide(s) NOTE : There would be no reaction between copper and zinc oxide because copper is LESS reactive. Aluminium(s) + iron oxide(s)  + iron(s) A MORE REACTIVE METAL CAN DISPLACE A LESS REACTIVE ONE FROM ITS OXIDE MORE REACTIVE Sodium (Na) Calcium (Ca) Magnesium (Mg) Aluminium (Al) Zinc (Zn) Iron (Fe) Lead (Pb) Copper (Cu) Gold (Au) Heat aluminium powder with powdered iron(III) oxide. The mixture flares up. The aluminium is displacing the iron from its oxide. The aluminium is taking the oxygen from the iron, leaving iron metal. LESS REACTIVE 2 2 Fe2O3  Al + Al2O3 + Fe NOT balanced

6. React with cold water : violent with acids A more vigorous reaction. Hot solution & lots of bubbles. A reaction of moderate speed. Steady production of bubbles. Acids are compounds containing hydrogen as the H+ ion. We must include hydrogen in the reactivity series. Less reactive than hydrogen. Cannot displace it. These metals have no reaction with acid. Metal + acid  salt + hydrogen (s) (aq) (aq) (g) REACTIONS OF METALS WITH ACIDS MORE REACTIVE Sodium (Na) Calcium (Ca) Magnesium (Mg) Aluminium (Al) Zinc (Zn) Iron (Fe) Lead (Pb) Hydrogen (H) Copper (Cu) Gold (Au) LESS REACTIVE Metals that are more reactive than hydrogen, displace it from the acid and set the hydrogen free as the gaseous element. zinc sulphate + hydrogen Zinc + sulphuric acid 

7.    hydrochloric acid balanced balanced balanced magnesium +  salt(aq) +hydrogen(g) metal(s) + acid(aq) Examples iron(II) sulphate + hydrogen iron + sulphuric acid  H2SO4 H2 FeSO4 + Fe + magnesium chloride + hydrogen HCl  2 Mg + MgCl2 + H2 lead nitrate NOT balanced lead + nitric acid  + hydrogen H2 2 HNO3 Pb(NO3) 2 + Pb + NOT balanced

8. EXTRACTING METALS FROM THEIR ORES. The earth’s crust contains metals and metal compounds, always found mixed with other substances. Gold is an unreactive metal, at the bottom of the reactivity series. It is found in the earth as the metal itself and chemical separation is not needed. In ORES, the metal or its compound is concentrated enough to make it economic to extract the metal. Often an ore contains a metal oxide or something that can easily be changed into a metal oxide. The ore haematite is iron(III) oxide, Fe2O3 The ore bauxite is aluminium oxide, Al2O3 To extract the metal, the oxygen must be removed from the metal oxide. ThIs process is called REDUCTION.

9. HOW A METAL IS EXTRACTED FROM ITS ORE DEPENDS ON HOW REACTIVE IT IS. Pass a stream of hydrogen gas over heated, black copper oxide. It will gradually go brown as copper metal is made. MORE REACTIVE Hydrogen will displace less reactive metals from oxides of those metals. Because its more reactive, it is able to remove the oxygen and combine with it to make water. Aluminium (Al) Zinc (Zn) Iron (Fe) Lead (Pb) Hydrogen (H) Copper (Cu) Silver (Ag) Gold (Au) So hydrogen can reduce ; silver oxide copper oxide Hydrogen cannot reduce ; lead oxide iron oxide zinc oxide, etc LESS REACTIVE copper oxide(s) + hydrogen(g) = copper(s) + water(g) H2  CuO + Cu + H2O

10. HOW CARBON CAN BE USED TO EXTRACT A METAL FROM ITS ORE.(this is an important, central point) Using first wood and then coal, this has been known about for thousands of years. (since the Iron Age) The difficulty of extracting aluminium from its oxide meant a stronger method, electrolysis, was needed & this is expensive. Electricity generation is a modern development. So we have only been able to extract the more reactive metals in recent times. Aluminium is MORE reactive than carbon and so carbon does NOT have the ability to remove oxygen from aluminium oxide. This is the position of the non-metal, carbon in the reactivity series. A metal such as iron, which is less reactive than carbon CAN be extracted from its ore using carbon. or zinc MORE REACTIVE Sodium (Na) Calcium (Ca) Magnesium (Mg) Aluminium (Al) Carbon (C) Zinc (Zn) Iron (Fe) Lead (Pb) Copper (Cu) Gold (Au) Because it is more reactive, carbon can take the oxygen from the iron oxide. As a result, iron is obtained from its ore using carbon in the Blast Furnace. Aluminium has to be extracted from Bauxite using ELECTROLYSIS. These two methods are considered in the following slides. LESS REACTIVE

11. The raw materials are : • coke (C) • haematite (Fe2O3) • limestone (CaCO3) waste gases  balanced carbon monoxide carbon dioxide + carbon  Hot air is blown in SLAG MOLTEN IRON EXTRACTION OF IRON IN THE BLAST FURNACE 1. The coke burns in an exothermic reaction. Energy is released, raw material gets hot and carbon dioxide is formed. 2. At the high temperatures, the carbon dioxide reacts with more coke to make carbon monoxide. 3. The carbon monoxide REDUCES the iron oxide in the ore, into molten iron which flows to the bottom of the furnace. carbon + oxygen  carbon dioxide C + O2  CO2 4. Limestone is added to remove acidic impurities forming a molten slag which floats on top of the iron. 2 CO2 + C  CO NOT balanced

12.  Hot air This is the central, important reaction in the Blast Furnace. balanced MOLTEN IRON carbon dioxide carbon monoxide Iron(III) oxide +  iron + SLAG This is REDUCTION This is OXIDATION The carbon monoxide REDUCES the iron oxide in the ore, into molten iron which flows to the bottom of the furnace. The process of removing oxygen from the ore is called REDUCTION. The carbon monoxide combines with the oxygen from the iron ore to produce carbon dioxide. This is called OXIDATION. Fe2O3 + CO  Fe + CO2 3 3 2 NOT balanced

13. connecting iron with a more reactive metal.“Galvanised iron” is the name given to iron plated with zinc. • The more reactive metal corrodes first, (zinc) making sure • the iron does NOT corrode. • That is why the zinc would be called a “sacrificial metal”. Here, the more reactive magnesium is being sacrificed, saving the iron pipe. wire • Steel can be mixed with other metals such as chromium (Cr) to make an alloy which will not rust. • Lots of cutlery made in Sheffield is manufactured from this “stainless steel”. underground iron pipe magnesium Theory of Electrolysis ALUMINIUM HOW CAN IRON BE PREVENTED FROM REVERTING TO ITS OXIDE ? Iron & steel corrode with air and water more quickly than most transition metals. It can be prevented by :

14. MAKING ALUMINIUM METAL INDUSTRIALLY USING ELECTROLYSIS. This large block of carbon is connected to the positive of the voltage supply. Al3+ MOLTEN ALUMINIUM OXIDE IN CRYOLITE O2- - + The lining of this large tank is made of carbon and is connected to the negative of the voltage supply. The ions are attracted as shown Oxygen forms at the positive electrode The aluminium forms at the negative electrode The raw material from which aluminium is produced is aluminium oxide, Al2O3 which contains the ions Al3+ and O2- The ore is called BAUXITE which needs purifying to get the aluminium oxide. The ions must be able to move but melting the aluminium oxide is difficult because of its high melting point. So the aluminium oxide is dissolved in molten aluminium compound called CRYOLITE at a much lower temperature. The oxide ion loses electrons and is oxidised : 2O2- - 4e  O2 This oxygen reacts with the carbon (+) electrode and makes carbon dioxide gas. So the electrode burns away quickly and often has to be replaced. The aluminium ion gains electrons and is reduced Al3+ + 3e  Al

15. Gets covered in a thin layer of aluminium oxide as soon as it is made. HOW CAN ALUMINIUM BE PREVENTED FROM REVERTING TO ITS OXIDE ? Aluminium is almost as reactive as magnesium & we might expect it to corrode quickly over time, or to burn up (oxidise) completely if it got hot. But it does not do this. Aluminium metal This surface layer forms a barrier to oxygen and water & so prevents further corrosion. Aluminium is a useful structural metal, low in density. It can be made harder, stronger & stiffer by mixing it will small amounts of other metals such as magnesium, to make an alloy.

16. is the copper ion, Cu2+ + + + + + + - - - - - impurities separated out REDUCTION AT THE NEGATIVE ELECTRODE The solution must contain the Cu2+ion Copper sulphate(aq) will do. OXIDATION AT THE POSITIVE ELECTRODE Cu2+ + e  Cu 2 Cu - e  Cu2+ 2 PURIFICATION OF COPPER - + The negative electrode is pure copper. The positive electrode is scrap copper containing impurities. - + - The scrap copper dissolves in the solution. Pure copper gets plated onto the negative electrode. + - - + - +

17. THE END These are the remains of some of the earliest Blast Furnaces. (Coalbrookdale Museum of Iron) This is a painting of the “Bedlam” Blast Furnaces at night, hundreds of years ago. To find out more about the Steel Industry, visit : The Ironbridge Gorge Museums, Telford Kelham Island Museum, Sheffield