1. Making Changes Topic overview

2. The topic can be conveniently split into six interrelated sections  Oxidation/Reduction  Salts  Preparation of gases  Metal extraction  Reactions of carbonates  Hydration

3. Oxidation & Reduction A substance is oxidised when  It gains oxygen  Or loses hydrogen 2Cu + O 2  2CuO Copper (Cu) is oxidised A substance is reduced when  It gains hydrogen  Or loses oxygen CuO + H 2  Cu + H 2 O Copper oxide (CuO) is reduced

4. Salts Are formed when a metal atom replaces the hydrogen atom(s) in an acid Are usually soluble The acids that are needed to be known about are Sulphuric acid - H 2 SO 4 - makes sulphates Hydrochloric acid - HCl- makes chlorides Nitric Acid - HNO 3 - makes nitrates

5. Metal oxide + acid  metal salt + water Magnesium Oxide + sulphuric Acid  magnesium sulphate + water MgO + H 2 SO 4  MgSO 4 + H 2 O Metal Hydroxide + acid  metal salt + water Sodium Hydroxide + Hydrochloric acid  sodium chloride + water NaOH + HCl  NaCl + H 2 O Metal carbonate + acid  metal salt + water + carbon dioxide Calcium carbonate + nitric acid  calcium nitrate + water + carbon dioxide CaCO 3 + HNO 3  Ca(NO 3 ) 2 + H 2 O + CO 2

6. Neutralisation  When an acid is added to an alkali  Equal amounts of the acid and alkali react together  Technique for measuring amounts is called titration  Titration can be used to measure concentrations of alkaline solutions and acids

7. Preparation of oxygen  Decomposition of hydrogen peroxide in the presence of manganese dioxide catalyst  Hydrogen peroxide  oxygen + water  H 2 O 2  O 2 + H 2 O Preparation of hydrogen  React a metal with acid  Magnesium + Hydrochloric acid  magnesium chloride + hydrogen  Mg + 2HCl  MgCl 2 + H 2

8. Collection of gases  Upward displacement of water – suitable for a low density, insoluble gas e.g. oxygen or hydrogen  Downward displacement of air – suitable for a dense, soluble gas e.g. chlorine  Gas syringe – suitable for soluble gases, e.g. ammonia or carbon dioxide

9. Tests for common gases  Oxygen- relights a glowing spill  Hydrogen- “pop” test with a lit spill  Carbon dioxide- turns limewater cloudy (or milky)  Ammonia- forms a white smoke with hydrochloric acid vapour  Chlorine- bleaches moist indicator paper

10. Metal extraction  An ore is any rock containing commercially useful amounts of a metal  Metals often found as oxides or sulphides  The method used to extract a metal depends upon the reactivity of that metal Unreactive metals (below hydrogen in the reactivity series) e.g. gold, platinum  Often found un-combined (or “native”) in the ore  Ore simply broken up and the pure metal extracted  Sometimes simple heating of the ore is required to extract the metal

11. Metals in the middle of the reactivity series (above hydrogen, below carbon)  Metal compound converted to oxide if not already  Heated with carbon, the metal is displaced by the carbon  Carried out in a blast furnace Reactive metals (above carbon in the reactivity series)  Extraction is more difficult  Either displacement using a more reactive metal (Titanium Chloride + sodium  titanium + sodium chloride)  Or use electrolysis (e.g. aluminium or sodium)

12. Carbonates  Decompose on heating (thermal decomposition) to give the oxide and carbon dioxide  Calcium carbonate  Calcium Oxide + carbon dioxide  CaCO 3  CaO + CO 2 Hydrogen carbonates  Decompose readily on heating to give the oxide, carbon dioxide and water  Sodium hydrogen carbonate  sodium oxide + carbon dioxide + water

13. Hydration  When a substance has water present it is said to be hydrated, If the water is removed it is dehydrated or anhydrous  E.g. anhydrous copper sulphate is a pale blue/grey colour, addition of a small amount of water to the anhydrous salt turns it into the dark blue hydrated salt.  Anhydrous copper sulphate + water  hydrated copper sulphate  CuSO 4 + 5H 2 O  CuSO 4.5H 2 O Dehydration is the reverse, for example heating the hydrated copper sulphate will give the anhydrous form and water