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Chemical Changes
AQA 2016 Chemistry topic 4

2. 4.1 Reactivity of Metals
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3. Metal Oxides Examples of metal oxides
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Examples of metal oxides
A metal oxide is a compound formed when a metal reacts with oxygen. Here are two examples:
Magnesium oxide – formed by burning magnesium
Oxidation = “adding oxygen”
Reduction = “reducing (taking away) oxygen”
Iron oxide – formed by iron rusting

4. Reactions of metals with water
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When a metal reacts with water hydrogen is always given off. The other product will be either a metal hydroxide or a metal oxide.
METAL + WATER METAL OXIDE + HYDROGEN
METAL + WATER METAL HYDROXIDE + HYDROGEN
Copy and complete the following reactions:
Sodium + water
Potassium + water
Calcium + water
Iron + steam

5. Words – gold, corroded, fizzes, disappear
Adding acids to metals
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If an acid is added to a (fairly reactive) metal the metal will be quickly ________ by the acid. We can see a reaction happening because the mixture _________ and the metal eventually __________.
Some metals, like ____, are so unreactive that nothing will happen.
Words – gold, corroded, fizzes, disappear

6. Reactions of metals with acids
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METAL + ACID SALT + HYDROGEN
e.g. magnesium + hydrochloric acid magnesium chloride + hydrogen Mg H Cl H Cl
Copy and complete the following reactions:
Calcium + hydrochloric acid
Zinc + hydrochloric acid
Iron + hydrochloric acid
Lithium + sulphuric acid

7. Reactivity Practical Task: to place six metals in order of reactivity
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Task: to place six metals in order of reactivity
Equipment: hydrochloric acid, calcium, copper, iron, aluminium, magnesium, zinc
Conclusion: I think the order of reactivity is…
Calcium
Magnesium
Aluminium
Zinc
Iron
Copper
The actual order of reactivity is:

8. The Reactivity Series Increasing reactivity
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Potassium
Sodium
Calcium
Magnesium
Aluminium
Carbon
Zinc
Iron
Lead
Hydrogen
Copper
Silver
Gold
Increasing reactivity
The Reactivity Series lists metals in order of reactivity:
Note the two non-metals in here!
The reactivity of these metals is related to their tendency to form positive ions.

9. What is the order of reactivity of these metals?
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What is the order of reactivity of these metals?
Metal
Reaction with dilute acid
Reaction with water
Reaction with oxygen A
Some reaction
Slow reaction
Burns brightly B
No reaction
Reacts slowly C D
Violent reaction E
Reasonable reaction
Reacts with steam only

10. Displacement reactions
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A displacement reaction is one where a MORE REACTIVE metal will DISPLACE a LESS REACTIVE metal from a compound. Mg
Magnesium
SO4 Cu
Copper sulphate
The magnesium DISPLACES the copper from copper sulphate
SO4 Mg
Magnesium sulphate Cu
Copper
Magnesium + copper sulphate magnesium sulphate + copper

11. Displacement Reactions
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Example 1 – Magnesium and copper sulphate O Cu S
Copper sulphate + Mg O S
Magnesium sulphate + Cu
Copper Mg
Magnesium
Example 2 – Zinc and copper sulphate Zn O Cu S
Zinc +
Copper sulphate
Copper
Zinc sulphate

12. Some example reactions…
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Reaction
Predicton
(yes or no?)
Observations
Lead + copper sulphate
Lead + iron sulphate
Zinc + copper sulphate
Zinc + iron sulphate
Copper + copper sulphate
Copper + iron sulphate
Reaction
No Reaction
Reaction
Reaction
No Reaction
No Reaction
Extension work – write down the equations for these reactions

13. Extracting Metals Some definitions:
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Some definitions:
A METAL ORE is a mineral or mixture of minerals from which it is “economically viable” to extract some metal.
Most ores contain METAL OXIDES (e.g. rust = iron oxide).
To “extract” a metal from a metal oxide we need to REDUCE the oxygen. This is called a REDUCTION reaction. To put it simply:
Oxide
Iron
Iron ore
“Reduce” the oxygen to make iron

14. Increasing reactivity
How do we do it?
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Potassium
Sodium
Calcium
Magnesium
Aluminium
Carbon
Zinc
Iron
Tin
Lead
Copper
Silver
Gold
Platinum
Increasing reactivity
Metals ABOVE CARBON, because of their high reactivity, are extracted by ELECTROLYSIS, which is very expensive!
Metals BELOW CARBON are extracted by heating them with carbon in a BLAST FURNACE. This is a “displacement reaction”
Carbon
Oxide
Iron
These LOW REACTIVITY metals won’t need to be extracted because they are SO unreactive you’ll find them on their own, not in a metal oxide

15. Extracting metals What is an ore?
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What is an ore?
In what form are metals usually found in the Earth?
How do you get a metal out of a metal oxide?
What is this type of reaction called?
Type of metal
Extraction process
Examples
High reactivity (i.e anything above carbon)
Middle reactivity (i.e. anything below carbon)
Low reactivity

16. Reduction and Oxidation
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Some examples of reduction:
Aluminium + iron oxide aluminium oxide + iron
heat
2Al(s) + Fe2O3(s) Al2O3(s) + 2Fe(s)
heat
Lead oxide + carbon lead + carbon dioxide
heat
2PbO(s) + C(s) Pb(s) + CO2(s)
heat
An example of oxidation:
Magnesium + oxygen magnesium oxide
heat
Mg(s) + O2(s) MgO(s)
heat

17. What is a Redox Reaction?
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Basically, during a redox reaction electrons are either lost or gained:
The Golden Rule: OILRIG
Oxidation Is Loss (of electrons)
Reduction Is Gain (of electrons)
For example:
Fe Fe2+
These reactions both involve the loss of electrons – they are Oxidation reactions
2Cl Cl2
Fe Fe
These reactions both involve the gain of electrons – they are Reduction reactions
Cl Cl-

18. 4.2 Reactions of Acids
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19. Reactions of metals with acids recap
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METAL + ACID SALT + HYDROGEN
e.g. magnesium + hydrochloric acid magnesium chloride + hydrogen Mg H Cl H Cl
Copy and complete the following reactions:
Calcium + hydrochloric acid
Zinc + hydrochloric acid
Iron + hydrochloric acid
Lithium + sulphuric acid

20. Redox reactions with acids and metals (higher only)
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Redox reactions with acids and metals (higher only)
Let’s consider one of the reactions on the previous page in more detail:
Zinc + hydrochloric acid Zinc chloride + hydrogen
Zn + 2HCl ZnCl2 + H2
During this reaction, the zinc atoms lose electrons to form a 2+ ion, ready to bond with two ions of chlorine (Cl-).
The hydrogen from the hydrochloric acid gains one electron to turn into a neutral diatomic atom.
The Golden Rule: OILRIG
Oxidation Is Loss (of electrons)
Reduction Is Gain (of electrons)
In other words, this is a REDOX reaction:

21. Common acids and alkalis
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Acids
Alkalis
Hydrochloric acid, HCl
Sodium hydroxide, NaOH
Nitric acid, HNO3
Potassium hydroxide, KOH
Sulphuric acid, H2SO4
Magnesium hydroxide, Mg(OH)2
Calcium hydroxide, Ca(OH)2

22. Quiz on acids and alkalis
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Acid, alkali or both???
This a pH of less than 7
This could kill cells
This is often used in cleaners or soap
This would turn Universal Indicator red
Sodium hydroxide is a common ____________
This would feel soapy on your skin
This could be a corrosive
This will turn universal indicator purple
This would taste sour
Lemon juice and vinegar are examples of weak _____

23. Neutralisation reactions
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A neutralisation reaction occurs when an acid reacts with an alkali. An alkali is a metal carbonate or metal hydroxide dissolved in water.
ACID + ALKALI SALT + WATER Na Cl H O
Copy and complete the following reactions:
Sodium hydroxide + hydrochloric acid
Calcium hydroxide + hydrochloric acid
Sodium hydroxide + sulphuric acid
Magnesium hydroxide + sulphuric acid

24. 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 and the acid is neutralised.
Carbonates used to be used as building materials but aren’t any more because acid rain would eventually ________ the building.
Words – dissolve, fizz, carbon dioxide, oxygen

25. Reactions of metals carbonates with acid
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A metal carbonate is an alkaline compound containing a metal, carbon and oxygen.
METAL CARBONATE + ACID SALT + CARBON DIOXIDE + WATER Mg H Cl C O
Copy and complete the following reactions:
Magnesium carbonate + hydrochloric acid
Calcium carbonate + hydrochloric acid
Sodium carbonate + sulphuric acid

26. Acids and metal hydroxides
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A neutralisation reaction occurs when an acid reacts with an alkali. An alkali is a metal oxide or metal hydroxide dissolved in water.
ACID + ALKALI SALT + WATER Na Cl H O
Copy and complete the following reactions:
Sodium hydroxide + hydrochloric acid
Calcium hydroxide + hydrochloric acid
Sodium hydroxide + sulphuric acid
Magnesium hydroxide + sulphuric acid

27. Reactions of metal oxides with acid
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A metal oxide is a compound containing a metal and oxide. They are sometimes called BASES. For example: Mg O Na Al
Magnesium oxide
Sodium oxide
Aluminium oxide
METAL OXIDE + ACID SALT + WATER Mg O H Cl
Copy and complete the following reactions:
Magnesium oxide + hydrochloric acid
Calcium oxide + hydrochloric acid
Sodium oxide + sulphuric acid

28. Making salts
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Whenever an acid and alkali or base neutralise each other we are left with a salt, like a chloride or a sulphate, and water. Complete the following table:
Hydrochloric acid
Sulphuric acid
Nitric acid
Sodium hydroxide
Sodium chloride + water
Potassium hydroxide
Potassium sulphate + water
Calcium hydroxide
Calcium nitrate + water

29. Required Practical 1 - Soluble Salts
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Method:
Neutralise an acid using a solid insoluble substance, such as a metal, metal oxide, metal hydroxide or metal carbonate. Keep adding the solid until an excess is left.
Filter off the excess to leave you with a salt solution.
Crystallise the solution to leave the salt.

30. Universal Indicator and the pH scale
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Universal Indicator is a mixture of liquids that will produce a range of colours to show how strong the acid or alkali is: 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Stomach acid
Lemon juice
Water
Soap
Baking powder
Oven cleaner
Strong alkali
Strong acid
Neutral

31. Acids and Alkalis
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Acids produce hydrogen ions when they dissolve in water: H Cl + -
Alkalis produce hydroxide ions: H O Na - +

32. Different indicators
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Litmus paper, used to simply indicate if something is acidic or alkaline
Universal indicator paper and pH meters, used to detect a pH value

33. Neutralisation reactions
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When acids and alkalis react together they will NEUTRALISE each other:
Sodium hydroxide
Hydrochloric acid Na H OH Cl
The sodium “replaces” the hydrogen from HCl Cl Na
Sodium chloride
H2O
Water
General equation: Acid + alkali or base Salt + water

34. Neutralisation reactions
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The basic equation for any neutralisation reaction is:
H+(aq) + OH-(aq) H2O(l)
Write word and chemical equations for the following reactions:
Hydrochloric acid + sodium hydroxide
Hydrochloric acid + potassium hydroxide
Nitric acid + potassium hydroxide
Sulphuric acid + calcium hydroxide
Nitric acid + copper oxide, CuO
Sulphuric acid + calcium carbonate, Ca(CO)3

35. Req. Practical 2 (Chem only) - Titration
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Req. Practical 2 (Chem only) - Titration
1) Fill a burette with sodium hydroxide solution of known concentration
2) Accurately measure out 25cm3 of acid and place it in the conical flask
3) Add phenolphthalein indicator to the flask
4) Slowly add the alkali until the mixture in the flask turns pink
5) Repeat until you get similar results

36. Titration Equations (higher only)
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Q. 0.05dm3 of HCl neutralises 0.1dm3 of NaOH of concentration 0.5mol dm-3. What is the concentration of the acid?
The key steps:
1) Look at the equation to compare the numbers of moles:
HCl + NaOH NaCl + H2O
Notice that 1 mole of HCl neutralises 1 mole of NaOH
2) Use this equation:
No. of moles = concentration x volume
So, the number of moles of NaOH is (0.5 x 0.1) = 0.05mol
According to the equation, this will neutralise 0.05mol of HCl
Therefore we have (0.05mol/0.05dm3) = 1mol dm-3 HCl

37. Titration Equations
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0.2dm3 of HCl neutralises 0.1dm3 of NaOH of concentration 0.5mol dm-3. What is the concentration of the acid?
H2SO4 of concentration 0.4mol dm-3 neutralises 0.1dm3 of NaOH of concentration 0.2mol dm-3. How much acid was used?
HCl + NaOH NaCl + H2O
H2SO4 + 2NaOH Na2SO4 + 2H2O

38. Universal Indicator and the pH scale
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Recall the pH scale: 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Stomach acid
Lemon juice
Water
Soap
Baking powder
Oven cleaner
Strong alkali
Strong acid
Neutral
A “strong” acid is one that is complete ionised in aqueous solutions. Examples are hydrochloric acid and sulphuric acid.
A weak acid is therefore only partly ionised in aqueous solutions. Examples are ethanoic, citric and carbonic acids.

39. More Information on Acids
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Fact 1: In the pH scale, if the pH decreases by one unit (e.g. 6 to 5) then the concentration of hydrogen ions has increased by a factor of 10.
Q. If hydrochloric acid has a pH of 1 and carbonic acid has a pH of 4, how many more hydrogen ions are in the HCl?
Conc. H2SO4
Fact 2: “strong” and “weak” refer to the degree if ionisation whereas “dilute” and “concentrated” refer to how much acid there is in a given volume.

40. 4.3 Electrolysis
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41. Testing for hydrogen
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“POP”

42. Testing for Oxygen
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Oxygen will relight a glowing splint

43. Testing for Chlorine Chlorine “bleaches” damp indicator paper
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Chlorine “bleaches” damp indicator paper

44. Electrolytes
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An electrolyte is an ionic substance that has been melted or dissolved in water so that the ions are free to move and conduct electricity:
Cl-
Na+
Cl-
Na+
Cl-
Na+
Cl-
Na+
Cl-
Na+
Cl-
Na+

45. Electrolysis ++++ ----
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Passing an electric current through an electrolyte will cause the ions to move:
Positive electrode
(“anode”)
++++
----
Negative electrode
(“Cathode”)
Cu2+
Cl-
Electrolyte solution containing copper ions and chloride ions
Cu2+
Cl-
Cu2+
Cl-

46. Electrolysis
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During electrolysis the substance being broken down is called the “electrolyte”.
= chloride ion
= copper ion
When we electrolysed copper chloride the _____ chloride ions moved to the ______ electrode and the ______ copper ions moved to the ______ electrode – OPPOSITES ATTRACT!!!

47. Electrolysis half equations
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We need to be able to write “half equations” to show what happens during electrolysis (e.g. for copper chloride):
At the negative electrode the positive ions GAIN electrons to become neutral copper ATOMS. The half equation is:
Cu e Cu 2
At the positive electrode the negative ions LOSE electrons to become neutral chlorine MOLECULES. The half equation is:
Cl e Cl2 2 2

48. Extracting Metals recap
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Potassium
Sodium
Calcium
Magnesium
Aluminium
Carbon
Zinc
Iron
Tin
Lead
Copper
Silver
Gold
Platinum
Increasing reactivity
Metals ABOVE CARBON, because of their high reactivity, are extracted by ELECTROLYSIS, which is very expensive as you need to melt the ore!
Displaced by carbon in a blast furnace
Don’t need to be extracted

49. Words – melting point, replaced, negative, bauxite, reactive, move
Extracting Aluminium
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Aluminium has to be extracted from its ore (called ________) by electrolysis. This is because aluminium is very ___________. The ore is mixed with cryolite to lower its ________ ________. The ore is then melted so that the ions can ______. The positively charged aluminium ions gather at the ___________ electrode. Oxygen forms at the positive electrode and causes it to wear away, which means that they have to be __________ frequently.
Words – melting point, replaced, negative, bauxite, reactive, move

50. Required Practical 3 - Electrolysis of Aqueous Solutions
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Required Practical 3 - Electrolysis of Aqueous Solutions
The ions discharged by electrolysis depend on the relative reactivity of the elements involved:
++++
----
At the positive electrode (anode), oxygen is produced UNLESS the solution contains halide ions, in which case a halogen is produced.
At the negative electrode (cathode), hydrogen is produced IF the metal is more reactive than hydrogen.
These patterns happen because in the aqueous solution water molecules break down, producing hydrogen ions and hydroxide ions that are then discharged.

51. Products from electrolysis
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Given these two rules, complete the following table:
Electrolyte
Product at cathode
Product at anode
Copper chloride solution
Copper sulfate solution
Sodium sulfate solution
Molten lead bromide
Copper
Chlorine
Copper
Oxygen
Hydrogen
Oxygen
Lead
Bromine

52. Redox reactions “Redox” reactions happen during electrolysis:
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“Redox” reactions happen during electrolysis:
At the positive electrode (anode) the negative ions LOSE electrons to become neutral – this is OXIDATION
At the negative electrode (cathode) the positive ions GAIN electrons to become neutral – this is REDUCTION
These two processes are called REDOX REACTIONS
OILRIG – Oxidation Is Loss of electrons
Reduction Is Gain of electrons

53. Electrolysis equations
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Try writing half equations for the electrolysis of copper sulfate…
At the negative electrode (cathode):
Cu2+ + 2e Cu
At the positive electrode (anode):
4OH- - 4e O2 + 2H2O