1. C5 Chemicals of the Natural Environment
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C5 Chemicals of the Natural Environment
OCR 21st Century
M Barker
Shirebrook Academy

2. The Earth 1) The atmosphere 2) The hydrosphere 3) The lithosphere
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1) The atmosphere
2) The hydrosphere
3) The lithosphere

3. C5.1 What types of chemicals make up the atmosphere?
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C5.1 What types of chemicals make up the atmosphere?

4. The Earth’s Atmosphere
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Present day atmosphere contains 78% nitrogen, 21% oxygen, 1% noble gases and about 0.04% CO2
Carbon dioxide, water vapour
Oxygen
Nitrogen
Noble gases

5. Molecular Compounds
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Most non-metal elements and compounds made from non-metals will form molecules, like hydrogen: H
Hydrogen has a very low melting point and a very low boiling point. Why?
2) When a substance is heated it is the intermolecular forces that are overcome, NOT the covalent bond in each molecule, which is much stronger!
1) The intermolecular forces are very weak so each one of these H2 molecules doesn’t really care about the others – it’s very easy to pull them apart.
Also, the molecules do not carry a charge so covalent compounds usually do not conduct electricity.

6. Chemicals in the Air Chemical Structure Diagram Boiling point/OC
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Chemical
Structure
Diagram
Boiling point/OC
Melting point/OC
Oxygen, O2
O=O
-183
-218
Nitrogen, N2
N=N
-196
-210
Carbon dioxide, CO2
O=C=O
-78
No liquid state
Water vapour, H2O
H-O-H
100
Argon. Ar Ar
-186
-189

7. More about Forces 1) Forces between molecules:
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1) Forces between molecules:
The forces between each molecule are very weak so the molecules can easily be pulled apart – this means they will have low boiling points.
2) Forces within the molecule:
Forces within the molecules are very strong due to the electrostatic attraction in a covalent bond caused by the protons attracting electrons.
Each line represents an electron being shared between the atoms

8. Other ways of drawing molecules
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Consider ammonia (NH3): H N H N H N

9. C5.2 What happens in the Hydrosphere?
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C5.2 What happens in the Hydrosphere?

10. The Hydrosphere
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Most of the Earth’s surface is water – we call this the “hydrosphere” and it consists of lakes, oceans, seas and rivers. These features contain lots of dissolved compounds called salts.

11. The Structure of salts – “a lattice”
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Cl-
Na+
When many positive and negative ions are joined they form a “giant ionic lattice” where each ion is held to the other by strong electrostatic forces of attraction (ionic bonds).
If these ions are strongly held together what affect would this have on the substance’s:
Melting point?
Boiling point?
State (solid, liquid or gas) at room temperature?

12. Chemicals of the hydrosphere - Water
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13. Dissolving a crystal lattice
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14. Dissolving Ionic Structures
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When an ionic structure like sodium chloride is dissolved it enables the water to conduct electricity as charge is carried by the ions:
Cl-
Na+
Cl-
Na+
Cl-
Na+
Cl-
Na+
Cl-
Na+
Cl-
Na+

15. 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

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

17. 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

18. Solubility rules
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The following guidelines are useful in working out if a substance will dissolve:
All common sodium, potassium and ammonium salts are soluble
All nitrates are soluble
Common chlorides are soluble but not silver and lead
Common sulfates are soluble but not those of lead, barium and calcium
Common carbonates and hydroxides are insoluble except those of sodium, potassium and ammonium

19. CaCl2 + 2NaOH Ca(OH)2 + 2NaCl
Precipitates
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Some metal compounds form precipitates, i.e. an insoluble solid that is formed when another ionic substance is added to them. Consider calcium chloride and sodium hydroxide:
CaCl NaOH Ca(OH)2 + 2NaCl
Ca OH Ca(OH)2
What precipitates are formed with the following metal compounds when they react with sodium hydroxide?
Metal compound
Precipitate formed
Soluble or insoluble?
Colour
Calcium chloride
Calcium hydroxide
White
Aluminium chloride
Magnesium chloride
Ammonium chloride

20. Testing for chloride and sulfate 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)

21. Testing for carbonate ions
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Limewater
Limewater turns milky/cloudy
Calcium carbonate + hydrochloric acid calcium chloride + carbon dioxide + water

22. C5.3 What types of chemicals make up the lithosphere?
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C5.3 What types of chemicals make up the lithosphere?

23. The Earth
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The lithosphere, the outer layer of the Earth, is made up of a mixture of minerals

24. Giant Covalent structures (“lattices”)
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Notice that giant covalent structures have very different properties to individual covalent molecules:
2. Graphite – carbon atoms arranged in a layered structure, with free _______ in between each layer enabling carbon to conduct _________ (like metals)
1. Diamond – a giant covalent structure with a very ____ melting point due to ______ bonds between carbon atoms
3. Silicon dioxide (sand) – a giant covalent structure of silicon and oxygen atoms with strong _____ causing a high ______ point and it’s a good insulator as it has no free electrons O Si
Words – melting, high, electrons, bonds, strong, electricity

25. Using Covalent Structures
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Form of carbon
Property
Uses
Why?
Carbon – diamond
Very hard
Drill tips
Extremely strong covalent structure
Graphite
Soft, conducts electricity
Lubricants and making electrodes
Graphite is arranged in layers that can slide over each other and it contains free electrons.

26. Elements in Rocks
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A lot of the silicon and oxygen in the lithosphere exists in the form of silicon dioxide (sand)

27. C5.4 How can we extract useful metals from rocks?
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C5.4 How can we extract useful metals from rocks?

28. “Reduce” the oxygen to make iron
Extracting Metals
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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

29. 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, cannot be extracted using carbon
Metals BELOW CARBON are extracted by heating them with carbon. This is a “displacement reaction”
Carbon
Oxide
Iron
Carbon + iron oxide carbon dioxide + 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

30. Sodium + water sodium hydroxide + hydrogen
Balancing equations
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Consider the following reaction:
Sodium + water sodium hydroxide + hydrogen 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”)

31. Balancing equations We need to balance the equation:
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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)

32. 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

33. Mass and atomic number revision
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Particle
Relative Mass
Relative Charge
Proton 1 +1
Neutron
Electron
Very small -1
MASS NUMBER = number of protons + number of neutrons He 2 4
SYMBOL
PROTON NUMBER = number of protons (obviously)

34. Relative formula mass, Mr
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The relative formula mass of a compound is the relative atomic masses of all the elements in the compound added together.
Relative atomic mass of O = 16
E.g. water H2O:
Relative atomic mass of H = 1
Therefore Mr for water = 16 + (2x1) = 18
Work out Mr for the following compounds:
HCl
NaOH
MgCl2
H2SO4
K2CO3
H=1, Cl=35 so Mr = 36
Na=23, O=16, H=1 so Mr = 40
Mg=24, Cl=35 so Mr = 24+(2x35) = 94
H=1, S=32, O=16 so Mr = (2x1)+32+(4x16) = 98
K=39, C=12, O=16 so Mr = (2x39)+12+(3x16) = 138

35. Calculating percentage mass
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If you can work out Mr then this bit is easy…
Percentage mass (%) =
Mass of element Ar
Relative formula mass Mr
x100%
Calculate the percentage mass of magnesium in magnesium oxide, MgO:
Ar for magnesium = 24 Ar for oxygen = 16
Mr for magnesium oxide = = 40
Therefore percentage mass = 24/40 x 100% = 60%
Calculate the percentage mass of the following:
Hydrogen in hydrochloric acid, HCl
Potassium in potassium chloride, KCl
Calcium in calcium chloride, CaCl2
Oxygen in water, H2O 3%
52%
36%
89%

36. Recap questions Work out the relative formula mass of:
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Work out the relative formula mass of:
Carbon dioxide CO2
Calcium oxide CaO
Methane CH4 44 56 16
Work out the percentage mass of:
Carbon in carbon dioxide CO2
Calcium in calcium oxide CaO
Hydrogen in methane CH4
27%
71%
25%

37. Calculating the mass of metal that can be extracted
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Calculating the mass of metal that can be extracted
This rock of iron oxide ore has a mass of 250g. How much iron could be extracted from it?
One possible method:
1) Iron oxide has a formula of Fe2O3. Use this information to calculate the percentage masses.
70% iron
2) Use the percentage mass of iron to calculate the mass of iron in the rock.
175g

38. Calculating the mass of metal
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After you’ve calculated the percentage mass you can work out the actual mass of a metal:
Mass of metal = % mass of metal x mass of substance
Calculate the mass of metal in the following:
Potassium in 10g of potassium chloride, KCl
Sodium in 20g of sodium chloride, NaCl
Calcium in 50g of calcium chloride, CaCl2
Magnesium in 100g of magnesium chloride, MgCl2
5.2g
7.9g
18g
25.3g

39. Solution containing copper and chloride ions
Electrolysis
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++++
----
Positive electrode
Negative electrode
Cu2+
Cl-
Solution containing copper and chloride ions
Cu2+
Cl-
Cu2+
Cl-

40. Electrolysis
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Electrolysis is used to separate a metal from its compound.
= 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!!!

41. Words – negative, reactive, move, electrons, molecules, atoms
Extracting Aluminium
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Aluminium has to be extracted from its ore by electrolysis. This is because aluminium is very ___________. The ore is then melted so that the ions can ______. The positively charged aluminium ions gather at the ___________ electrode where they gain ________ to become neutral atoms. Oxide ions move to the positive electrode where they lose electrons to become oxygen ____ which then combine to form oxygen ________.
Words – negative, reactive, move, electrons, molecules, atoms

42. Copper, Aluminium and Titanium
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Metal
Uses and why
Extraction method
Problems
Copper
Electrical wires – good conductor
Electrolysis
Limited supply
Aluminium and titanium
Planes – light and corrosion resistant
Complicated and expensive
Expensive and difficult to extract

43. Metals
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Metal atoms are very closely packed together in a regular arrangement. The atoms are held together by metallic bonds that cause the metal to usually have high melting and boiling points.

44. Properties of metals
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Metals have very high melting points (which means that they are usually _____) whereas non-metals will melt at lower ___________
All metals conduct heat and __________ very well, whereas non-metals don’t (usually)
Metals are strong and ______ but bendable. Non-metals are usually _____ or they will snap.
Metals will _____ when freshly cut or scratched, whereas non-metals are usually dull.
Metals have higher _______ than non-metals (i.e. they weigh more)
Metals can be used to make ______ (a mixture of different metals)
Words - alloys, electricity, solids, weak, densities, temperatures, tough, shine

45. Words – slip, electrons, melting, electricity, strong, ions
A closer look at metals
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Metals are defined as elements that readily lose ______ to form positive ____. The ions are closely packed (hence the metal is ______) and they have strong bonds holding them together (hence the high _______ points). The presence of free electrons means that metals can conduct ______. Metals can bend because the layers can “____” over each other:
Words – slip, electrons, melting, electricity, strong, ions + + + + + + + + + + +