19/09/2018 Chemistry in Action W Richards The Weald School

Sodium + water sodium hydroxide + hydrogen Balancing equations 19/09/2018 Consider the following reaction: Sodium + water sodium hydroxide + hydrogen Na + H2O NaOH + H2 Na O H O H Na + H + This equation doesn’t balance – there are 2 hydrogen atoms on the left hand side (the “reactants” and 3 on the right hand side (the “products”)

Balancing equations We need to balance the equation: 19/09/2018 We need to balance the equation: Sodium + water sodium hydroxide + hydrogen Na O H O H Na O H Na O H + H + Na Now the equation is balanced, and we can write it as: 2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)

Some examples 2 2 3 2 3 Mg + O2 Zn + HCl Fe + Cl2 NaOH + HCl CH4 + O2 19/09/2018 2 2 3 2 3 Mg + O2 Zn + HCl Fe + Cl2 NaOH + HCl CH4 + O2 Ca + H2O NaOH + H2SO4 CH3OH + O2 MgO ZnCl2 + H2 FeCl3 NaCl + H2O CO2 + H2O Ca(OH)2 + H2 Na2SO4 + H2O 2 2 4

Testing for carbon dioxide 19/09/2018 Gas Limewater Limewater turns milky/cloudy

Adding acid to carbonates 19/09/2018 Carbonates are compounds containing carbon and oxygen. When an acid is added to a carbonate the carbonate starts to _______. A gas called ______ _______ is produced. Carbonates used to be used as building materials but aren’t any more because acid rain would eventually ________ the building. Calcium carbonate + hydrochloric acid calcium chloride + carbon dioxide + water CaCO3(s) + HCl(aq) CaCl2(aq) + CO2(g) + H2O(l) Words – dissolve, fizz, carbon dioxide, oxygen

Flame tests 19/09/2018 Compound Colour of flame

Flame tests 19/09/2018 Compounds containing lithium, sodium, potassium, calcium and barium can be recognised by burning the compound and observing the colours produced: Lithium Red Sodium Yellow Potassium Lilac Calcium Brick red Barium Green

Calcium chloride has the formula CaCl2 Metal ions 19/09/2018 Metal compounds in a solution contain metal ions. For example, consider calcium chloride: Calcium is in group 2 and has two electrons in its outer shell, so it will form a Ca2+ ion. Chlorine is in group 7 so a chloride ion will be Cl- Calcium chloride has the formula CaCl2

Metal ions and precipitates 19/09/2018 Some metal ions form precipitates, i.e. an insoluble solid that is formed when sodium hydroxide is added to them. Consider calcium chloride: Ca2+(aq) + OH- Ca(OH)2 (s) 2

Metal ions and precipitates 19/09/2018 Some metal ions form precipitates, i.e. an insoluble solid that is formed when sodium hydroxide is added to them. Consider calcium chloride: Ca2+(aq) + OH- Ca(OH)2 (s) 2 Metal ion Precipitate formed Colour Calcium Ca2+ Calcium hydroxide: Ca2+(aq) + OH-(aq) Ca(OH)2 (s) White Aluminium Al3+ Magnesium Mg2+ Copper(II) Cu2+ Iron(II) Fe2+ Iron(III) Fe3+

Testing for chloride and sulphate ions 19/09/2018 For each test state: 1) The colour of the precipitate 2) What compound it is Test 1: Chloride ions Add a few drops of dilute nitric acid to the chloride ion solution followed by a few drops of silver nitrate. Precipitate formed = silver chloride (white) Test 2: Sulphate ions Add a few drops of dilute hydrochloric acid to the sulphate ion solution followed by a few drops of barium chloride. Precipitate formed = barium sulphate (white again)

Ammonium, nitrate, bromide and iodide ions 19/09/2018 Ammonium ions: Add sodium hydroxide and test the gas using damp litmus paper – ammonia gas turns damp litmus paper blue. Nitrate ions: Add sodium hydroxide followed by aluminium powder and test using damp litmus paper. Bromide and iodide ions: Add a few drops of dilute nitric acid followed by a few drops of silver nitrate solution. A pale yellow precipitate should be formed for bromide ions and a darker yellow precipitate for iodide ions.

Thermal decomposition 19/09/2018 A “thermal decomposition” reaction occurs when a compound breaks down (“decomposition”) through the action of heat. Practical work: Perform a thermal decomposition reaction on each of these compounds and state: The colour changes you observed The reaction that happened Copper carbonate: CuCO3 (s) CuO(s) + CO2 (g) (Green – Black) Zinc carbonate: ZnCO3 (s) ZnO(s) + CO2 (g) (White – Yellow)

How sulphuric acid is made: 19/09/2018 Sulphuric acid has many important uses – car batteries, detergents, fertilisers etc. How sulphuric acid is made: Step 1: Burn sulphur in air: Sulphur + oxygen sulphur dioxide Step 2: Pass the sulphur dioxide over a vanadium oxide catalyst at 450OC: Sulphur dioxide + oxygen sulphur trioxide Step 3: Dissolve the sulphur trioxide in sulphuric acid: Sulphur trioxide + conc. sulphuric acid oleum Step 4: Add water to the oleum: Oleum + water sulphuric acid

Endothermic reactions Reversible Reactions 19/09/2018 When a reversible reaction occurs in a CLOSED SYSTEM (i.e. no reactants are added or taken away) an EQUILIBRIUM is achieved – in other words, the reaction goes at the same rate in both directions: A + B C D Endothermic reactions Increased temperature: Decreased temperature: Exothermic reactions Increased temperature: Decreased temperature: A + B C D A + B C D More products Less products A + B C D A + B C D Less products More products

Solution – use 450OC as a compromise Sulphuric acid 19/09/2018 Step 2 in the manufacture of sulphuric acid is an example of a reversible reaction: Endothermic Exothermic 2SO2 + O2 2SO3 What would happen if the temperature was decreased? The reaction would favour the production of sulphur trioxide BUT the reaction would happen at a slower rate. Solution – use 450OC as a compromise

Words – slag, brittle, steel, oxygen, acidic Iron and Steel 19/09/2018 In previous work we considered the role of the blast furnace in extracting iron from its ore. The iron contains roughly 5% carbon and different metals and is very ________. In order to reduce these impurities and convert the iron into _________ the molten iron is transferred into another furnace where it is mixed with recycled scrap iron and pure ___________. The oxygen reacts with the metal impurities to form ________ oxides. Calcium carbonate is also added to remove some of the acidic oxides as _______ when the furnace is tilted. Words – slag, brittle, steel, oxygen, acidic

Making steel – the reactions 19/09/2018 1) Mixing oxygen with silicon impurities: Silicon + oxygen Silicon oxide 2) Decomposition of limestone: Calcium carbonate calcium oxide + carbon dioxide 3) Adding these products together: Silicon oxide + calcium oxide calcium silicate Steel with a high carbon content is strong but brittle Steel with a low carbon content is easily shaped Steel with chromium and nickel is called stainless steel

Titanium chloride + sodium titanium + sodium chloride 19/09/2018 Titanium is a strong metal used in planes, replacement hip joints, bikes etc. Two steps are used in its manufacture: Step 1: Convert titanium dioxide (ore) to titanium chloride Step 2: Displace the titanium using sodium or magnesium: Titanium chloride + sodium titanium + sodium chloride In this reaction the titanium is displaced my a more reactive metal. This reaction is done in an argon atmosphere to avoid any further reactions. Titanium ions have a charge of 4+ and gain four electrons to become titanium atoms. This is a reduction reaction.

Aluminium 19/09/2018 Aluminium is a fairly reactive metal that doesn’t corrode due to forming a thin layer of aluminium oxide. This explains why greenhouses don’t rust and don’t need to be painted. A thicker layer of aluminium oxide can be made artificially. There are two stages: ++++ ---- H2SO4 Al 1) Remove the natural layer by placing the aluminium in sodium hydroxide. 2) Use electrolysis on sulphuric acid with the aluminium as the positive electrode. This is called anodising.

Solution containing silver ions Electroplating 19/09/2018 ++++ ---- Silver electrode Object to be plated Solution containing silver ions