true or false in a ‘reduction’ reaction oxygen is added to a metal in electrolysis a positive...
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True or FalseTrue or FalseIn a ‘reduction’ reaction Oxygen is added to a metal
In electrolysis a positive ion is attracted to the positive electrode (anode)
Organic chemicals found in the Biosphere are often formed around chains of CARBON atoms
Photosynthesis adds carbon to the atmosphere
Chemicals of the atmosphere have high boiling points and are made up of molecules containing lots of atoms
Giant covalent structures such as Silicon Dioxide have high melting points
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OCR Additional ScienceOCR Additional ScienceChemicals of the Natural Chemicals of the Natural
EnvironmentEnvironment
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The EarthThe Earth
1) The atmosphere
2) The hydrosphere
3) The biosphere
4) The lithosphere
19/04/23The Carbon The Carbon CycleCycle
CO2 in air
Photosynthesis
Respiration
Carbon is eaten by animals
Death of animals
Microbes respiring
Respiration
CO2 dissolves into the ocean
Death of plants
Sediment pressurized
Cement making
Fossil fuels
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The Nitrogen CycleThe Nitrogen Cycle1. Nitrogen-fixing bacteria convert N2 in the air into nitrates
2. Plants are then eaten by animals – the nitrogen becomes PROTEIN
3. Decomposers break down waste products and dead animals and plants to form AMMONIUM COMPOUNDS
4. Denitrifying bacteria convert nitrates and ammonium compounds into atmospheric nitrogen
Nitrates in the soil
Waste and dead animals
6. Nitrates taken in by plants
N2 in air
5. Nitrifying bacteria convert ammonium compounds into nitrates
Lightn
ing
Denitrifyin
g
bacte
ria
1. Fe
rtilisers
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Chemicals in the AirChemicals in the AirChemical Structure Diagram Boiling
point/OCMelting point/OC
Oxygen, O2 O=O -183 -218
Nitrogen, N2 N=N -196 -210
Carbon dioxide, CO2
O=C=O -78No liquid state
Water vapour, H2O
H-O-H 100 0
Argon. Ar Ar -186 -189
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ForcesForces1) Forces between molecules:
2) Forces within the molecule:
The forces between each molecule are very _____ so the molecules can _____ be pulled apart.
Forces within the molecules are very ______ due to the _______ bond so its very difficult to pull apart each molecule
Each line represents an electron being shared between the atoms
19/04/23Chemicals of the hydrosphere - WaterChemicals of the hydrosphere - Water
e-e- e-
e-
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Dissolving a crystal latticeDissolving a crystal lattice
-
-
-
- -
+
+ +
++
19/04/23Chemicals of the Chemicals of the lithosphere - Silicon lithosphere - Silicon
DioxideDioxide
O OO
O
Si
O O
OSi
OO
O
Si
Silicon dioxide forms a giant ______ structure where each atom is covalently bonded, forming a very strong 3-D ______. This causes it to be _____, have high _____ and boiling points and a good electrical ________.
Words – melting, covalent, insulator, hard, structure
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Using Covalent StructuresUsing Covalent StructuresElement/ compound
Property Uses Why?
Carbon – diamond
Very hard Drill tips Extremely strong covalent structure
Silicon dioxide
High melting point (1610OC)
Furnace linings
Very difficult to melt
Silica glass Doesn’t conduct electricity
Electrical insulators
No free electrons to carry charge
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Chemicals of the biosphereChemicals of the biosphere
GlucoseDNA
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Balancing equationsBalancing equationsConsider the following reaction:
Na
O
H HH H
Na
OH
Sodium + water sodium hydroxide + hydrogen
+ +
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”)
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Balancing equationsBalancing equationsWe need to balance the equation:
Na
O
H H
H H
Na
OH
Sodium + water sodium hydroxide + hydrogen
+ +
Na
O
H HNa
OH
Now the equation is balanced, and we can write it as:
2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)
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Some examplesSome examples
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
CO2 + H2O
2
2
2 3
2
2
2
2 3
2
2
2
2
2 4
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Extracting MetalsExtracting Metals
A METAL ORE is a mineral or mixture of minerals from which it is “economically viable” to extract some metal.
To “extract” a metal from a metal oxide we need to REDUCE the oxygen. This is called a REDUCTION reaction. To put it simply:
Most ores contain METAL OXIDES (e.g. rust = iron oxide).
Some definitions:
Iron OxideIron ore
“Reduce” the oxygen to make
iron
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OxideIron
How do we do it?How do we do it?Potassium
Sodium
Calcium
Magnesium
Aluminium
Carbon
Zinc
Iron
Tin
Lead
Copper
Silver
Gold
Platinum
Metals ABOVE CARBON, because of their high reactivity, are extracted by ELECTROLYSIS
Metals BELOW CARBON are extracted by heating them with carbon in a BLAST FURNACE. This is a “displacement reaction”
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
Carbon
19/04/23Calculating percentage Calculating percentage massmass
Calculate the percentage mass of magnesium in magnesium oxide, MgO:
Ar for magnesium = 24 Ar for oxygen = 16
Mr for magnesium oxide = 24 + 16 = 40
Therefore percentage mass = 24/40 x 100% = 60%
Percentage mass (%) =
Mass of element Ar
Relative formula mass Mr
x100%
Calculate the percentage mass of the following:
1) Hydrogen in hydrochloric acid, HCl
2) Potassium in potassium chloride, KCl
3) Calcium in calcium chloride, CaCl2
4) Oxygen in water, H2O
19/04/23Calculating the mass of Calculating the mass of metalmetal
After you’ve calculated the percentage mass you can work out the actual mass of a metal:
Calculate the mass of metal in the following:
1) Potassium in 10g of potassium chloride, KCl
2) Sodium in 20g of sodium chloride, NaCl
3) Calcium in 50g of calcium chloride, CaCl2
4) Magnesium in 100g of magnesium chloride, MgCl2
Mass of metal = % mass of metal x mass of substance
19/04/23Life Cycle Assessments Life Cycle Assessments (LCAs)(LCAs)
Step 1: Manufacture
What resources are needed? What effect will this have on the environment?
Step 2: Use
How much energy will be needed? What is the effect on the environment?
Step 3: Disposal
How is the product disposed of? What is the effect on the environment?
19/04/23ElectrolysisElectrolysis
++++
----
Positive electrode
Cu2+
Cu2+
Cu2+
Negative electrode
Cl-
Cl-
Cl-
Solution containing copper and
chloride ions
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ElectrolysisElectrolysisElectrolysis 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!!!
19/04/23Electrolysis equationsElectrolysis equationsWe need to be able to write “half equations” to show what happens during electrolysis (e.g. for copper chloride):
2 2
2
At the negative electrode the positive ions GAIN electrons to
become neutral copper ATOMS. The half equation is:
Cu2+ + e- Cu
At the positive electrode the negative ions LOSE electrons to
become neutral chlorine MOLECULES. The half equation is:
Cl- - e- Cl2
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Extracting AluminiumExtracting Aluminium
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
19/04/23Electrolysis of Aluminium Electrolysis of Aluminium OxideOxide
Overall:
At the cathode: At the anode:
Al3+(l) + 3e- Al(l) 2O2-
(l) - 4e- O2(g)
Aluminium oxide aluminium + oxygen
2Al2O3(l) 4Al(l) + 3O2(g)
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Using IronUsing Iron
Iron produced by the blast furnace (“cast iron”) contains about 96% iron and 4% impurities. These impurities make it very brittle and easy to break.
Ironbridge, Shropshire – made out of cast iron and safe for horses and carts but not modern vehicles.
19/04/23Copper, Aluminium and Copper, Aluminium and TitaniumTitanium
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
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MetalsMetals
Metal atoms are very closely packed together in a regular arrangement. The atoms are held together by metallic bonds.
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Properties of metalsProperties of metals
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
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A closer look at metalsA closer look at metals
+ + + + +
+ + + + ++ + + + ++ + + + ++ + + + +
+ + + + +
+ + + + +
+ + + + ++ + + + +
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