1. Predicting and Identifying Reactions and Products
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10/11/2018
Predicting and Identifying Reactions and Products
OCR Gateway 2016 Chemistry topic 4
“POP”
W Richards
The Weald School

2. C4.1 Predicting Chemical Reactions
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C4.1 Predicting Chemical Reactions

3. Recap: The Periodic table
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Mendeleev
The periodic table arranges all the 100 or so elements in groups according to their properties.
Vertical columns are called GROUPS
Horizontal rows are called PERIODS

4. Group 0 – The Noble gases He Ne Ar Kr Xe Rn Questions:
10/11/2018 He Ne Ar Kr Xe Rn
Questions:
How many electrons do these elements have in their outer shell?
How does this affect their reactivity?

5. Words – neon, stable, low, shell, atoms, increases
Group 0 – The Noble gases
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Some facts…
All of the noble gases have a full outer ______.
They all have _____ melting and boiling points and are inflammable.
3) They exist as single _______.
Their boiling point ______ as atomic mass increases.
5) Because they have a full outer shell, the noble gases are ______ and unreactive.
Words – neon, stable, low, shell, atoms, increases

6. Group 1 – The alkali metals
10/11/2018 Li Na K Rb Cs Fr

7. Group 1 – The alkali metals
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Some facts…
1) These metals all have ___ electron in their outer shell.
2) They are not very ________
3) Reactivity increases as you go _______ the group.
4) They all react with water to form an alkali (hence their name) and __________, e.g:
Potassium + water potassium hydroxide + hydrogen
2K(s) H2O(l) KOH(aq) H2(g)
5) They form ionic compounds – white solids that dissolve in ______ to form ________ solutions (e.g. salt water).
Words – down, one, hydrogen, dense, colourless, water

8. Properties of the Alkali Metals
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Element
Melting Point (OC)
Boiling Point (OC)
Density (g/cm3)
Lithium
180
1340
0.53
Sodium 98
883
0.97
Potassium 64
760
0.86
Rubidium 39
688
1.53
Caesium ??

9. Trends in Group 1 Consider a sodium atom: +
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Consider a sodium atom: +
Take away one of the electrons (“oxidation”)
Sodium ion
Now consider a potassium atom: +
Take away one of the electrons
Potassium ion
Potassium loses its electron more easily because its further away – potassium is MORE REACTIVE

10. Group 7 – The halogens
10/11/2018 F Cl Br I At

11. Words – diatomic, liquid, decreases, water, ionic
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Group 7 – The Halogens
Decreasing
reactivity
Some facts…
1) Reactivity ______ as you go down the group. Cl
2) They exist as _______ molecules (so that they both have a full outer shell): Cl
3) Because of this fluorine and chlorine are _____ at room temperature and bromine is a gas.
4) They react with metals to form ______ compounds, e.g. salt.
5) They form molecular compounds with other non-metallic compounds, e.g. _______.
Words – diatomic, liquid, decreases, water, ionic

12. Properties of Group 7 Element Melting Point (OC) Boiling Point (OC)
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Element
Melting Point (OC)
Boiling Point (OC)
Density (g/cm3)
Flourine
-220
-188
0.0016
Chlorine
-101
-34
0.003
Bromine -7 59
3.12
Iodine
114
184
4.95
Astatine ??

13. Add an electron (“reduction”)
Trends in Group 7
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Consider a fluorine atom: -
Add an electron (“reduction”)
Fluoride ion
Now consider a chlorine atom: -
Add an electron
Chloride ion
Chlorine doesn’t gain an electron as easily as fluorine so it is LESS REACTIVE

14. The halogens – some reactions
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1) Halogen + metal: Na + Cl - Na Cl +
Note that the halogen will have a charge of -1
Halogen + metal ionic salt
2) Halogen + non-metal: Cl Cl H H +
Halogen + non-metal covalent molecule

15. Displacement reactions
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To put it simply, a MORE reactive halogen will displace a LESS reactive halogen from a solution of its salt.
Potassium chloride KCl(aq)
Potassium bromide KBr(aq)
Potassium iodide KI (aq)
Chlorine Cl2
Bromine Br2
Iodine I2 F Cl Br I
Decreasing reactivity

16. Words – hard, coloured, higher, mercury, less, catalyst, insoluble
The Transition Metals
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Some facts…
1) They are all ______ and solid (except _________).
2) They are ____ reactive than the alkali metals.
3) They can form __________ compounds, usually _______.
They can be used as a ______ (a chemical that speeds up a reaction).
They have ______ melting points and densities compared to group 1.
Words – hard, coloured, higher, mercury, less, catalyst, insoluble

17. Examples of Reactions + + Magnesium chloride: Cl Cl Mg Mg Cl Cl MgCl2
10/11/2018 Cl -
Magnesium chloride: Cl Mg 2+ Mg + Cl - Cl
MgCl2
Calcium oxide: O Ca + 2+ 2-
CaO

18. Balancing ions Some common ions:
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Some common ions:
Sodium – Na+
Potassium – K+
Magnesium – Mg2+
Ammonium – NH4+
Chloride – Cl-
Bromide – Br-
Oxide – O2-
Sulphate – SO42-
Determine the formula of these compounds:
Sodium chloride
Magnesium oxide
Magnesium chloride
Ammonium chloride
Sodium sulphate
Sodium oxide
Answers:
NaCl
MgO
MgCl2
NH4Cl
Na2SO4
NaO

19. 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

20. 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

21. 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

22. 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:

23. 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.

24. 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

25. C4.2 Identifying the Products of Reactions
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C4.2 Identifying the Products of Reactions

26. Testing for hydrogen
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“POP”

27. Testing for Oxygen
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Oxygen will relight a glowing splint

28. Testing for Carbon Dioxide
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Limewater
Limewater turns milky/cloudy
Calcium carbonate + hydrochloric acid calcium chloride + carbon dioxide + water

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

30. Precipitation Reactions
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A precipitation reaction occurs when an insoluble solid is made by mixing two ionic solutions together.
Method:
1) Mix the reactants together
2) Filter off the precipitate
3) Wash the residue
4) Dry the residue in an oven at 50OC

31. Metal Hydroxides
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Sodium hydroxide can be used to identify some metal ions (cations). 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+
Aluminium hydroxide: Al3+(aq) + OH-(aq) Al(OH)3(aq)
Zinc Zn2+
Zinc hydroxide: Zn2+(aq) + OH-(aq) Zn(OH)2 (s)
Copper(II) Cu2+
Copper hydroxide: Cu2+(aq) + OH-(aq) Cu(OH)2 (s)
Blue
Iron(II) Fe2+
Iron(II) hydroxide: Fe2+(aq) + OH-(aq) Fe(OH)2 (s)
Green
Iron(III) Fe3+
Iron(III) hydroxide: Fe3+(aq) + OH-(aq) Fe(OH)3(aq)
Brown
Q. Can you complete this table?

32. Testing for halide 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)
Ag+(aq) + Cl-(aq) AgCl(s)
Test 2: Bromide and iodide ions:
Add a few drops of dilute nitric acid followed by a few drops of silver nitrate solution again. A pale yellow precipitate should be formed for bromide ions and a darker yellow precipitate for iodide ions.

33. Testing for Carbonate and Sulphate ions
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Method:
Add a few drops of dilute hydrochloric acid to the carbonate or sulphate ion solution followed by a few drops of barium chloride.
e.g. Precipitate formed = barium sulphate (white again)

34. Flame tests
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Compound
Colour of flame

35. Q. What would happen if you used a mixture of chemicals?
Flame tests
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Compounds containing lithium, sodium, potassium, calcium and copper metal ions (“cations”) can be recognised by burning the compound and observing the colours produced:
Lithium
Red
Sodium
Yellow
Potassium
Lilac
Calcium
Brick red
Copper
Green
Q. What would happen if you used a mixture of chemicals?

36. Instrumental Methods
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Hi. We’re industrial scientists and we want to test for ions but use instrumental methods instead of things like flame tests. What are the advantages of doing these tests instrumentally?
Advantages of instrumental methods:
More accurate
More sensitive
Quicker

37. Flame Emission Spectroscopy
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Flame emission spectroscopy is an example of an instrumental method:
Step 1: Burn the chemical and pass the light through a spectroscope:
Step 2: Analyse the line spectrum output to identify the metal ion:
Unknown ion
Potassium
Calcium