1. 19/09/2018
Chemistry in Action
W Richards
The Weald School

2. Sodium + water sodium hydroxide + hydrogen
Balancing equations
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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”)

3. 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) NaOH(aq) + H2(g)

4. Some examples 2 2 3 2 3 Mg + O2 Zn + HCl Fe + Cl2 NaOH + HCl CH4 + O2
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Mg O2
Zn HCl
Fe Cl2
NaOH HCl
CH O2
Ca H2O
NaOH H2SO4
CH3OH O2
MgO
ZnCl H2
FeCl3
NaCl H2O
CO H2O
Ca(OH) H2
Na2SO H2O 2

5. Testing for carbon dioxide
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Gas
Limewater
Limewater turns milky/cloudy

6. Adding acid to carbonates
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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

7. Flame tests
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Compound
Colour of flame

8. Flame tests
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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

9. 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

10. Metal ions and precipitates
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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

11. Metal ions and precipitates
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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+

12. Testing for chloride and sulphate ions
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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)

13. Ammonium, nitrate, bromide and iodide ions
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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.

14. Thermal decomposition
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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)

15. How sulphuric acid is made:
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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

16. Endothermic reactions
Reversible Reactions
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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

17. Solution – use 450OC as a compromise
Sulphuric acid
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Step 2 in the manufacture of sulphuric acid is an example of a reversible reaction:
Endothermic
Exothermic
2SO2 + O SO3
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

18. Words – slag, brittle, steel, oxygen, acidic
Iron and Steel
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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

19. Making steel – the reactions
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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

20. Titanium chloride + sodium titanium + sodium chloride
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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.

21. Aluminium
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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.

22. Solution containing silver ions
Electroplating
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++++
----
Silver electrode
Object to be plated
Solution containing silver ions