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GCSE - chemistry > CC11 - extracting Metals & CC12 - reversible reactions and equilibria > Flashcards

CC11 - extracting Metals & CC12 - reversible reactions and equilibria Flashcards

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1
Q

What is oxidation

A

When oxygen is added to a substance (loss of electrons)

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2
Q

What is reduction

A

When oxygen is removed from a substance (gain of electrons)

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3
Q

What is a redox reaction

A

A reaction where both oxidation and reduction occur

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4
Q

What is a sign that a reaction has occurred

A

Effervescence (more = higher reactivity)

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5
Q

What gas is produced when metals are reacted with acid

A

Hydrogen

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6
Q

What is the test for hydrogen

A

Hold a lit splint to the gas, if hydrogen is present there will be a squeaky pop

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7
Q

Word equation for metals reacting with acid

A

Metal + acid —> salt + hydrogen

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8
Q

Word equation for metal reacting with water

A

Metal + water —> metal hydroxide + hydrogen

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9
Q

Example of a redox reaction

A

Displacement reactions

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10
Q

What occurs during a displacement reaction

A

A more reactive element reacts to take the place of a less reactive element in a compound

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11
Q

Redox in metal displacement reactions

A

More reactive metal = lose electrons (oxidation)
Less reactive metal = gain electrons (reduction)

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12
Q

What happens when a reactive metal is put in a solution of a less reactive metal salt

A

The reactive metal will react to take the place of the less reactive metal in the salt compund

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13
Q

What happens if a less reactive metal is added to a solution of a more reactive metal salt

A

Nothing, a less reactive metal cannot take the place of a more reactive metal

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14
Q

What happens if a metal is added to a solution of a metal salt of the same metal

A

Nothing, the same metal cannot displace itself

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15
Q

What is an ore

A

A rock that contains a compound with enough metal to make extracting the metal economically viable

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16
Q

What is economically viable

A

It make sense financially eg. Profit can be made

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17
Q

Copper ore

A

Malachite

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18
Q

Aluminium ore

A

Bauxite

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19
Q

Iron ore

A

Hematite

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20
Q

What does the method used to extract the metal from its ore depend on

A

How reactive it is

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21
Q

Why are gold and platinum present in the earth as uncombined elements

A

They are very unreactive

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22
Q

What does extracting metals by reduction using carbon depend on

A

It only works if the metal is less reactive than carbon

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23
Q

Word equation for extraction using carbon

A

Metal oxide + carbon —> metal + carbon dioxide

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24
Q

How are metals that are more reactive than carbon extracted from their ores

A

Electrolysis

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25
Q

Why is electrolysis only used for metals more reactive than carbon

A

It is more expensive to run as it involves large amounts of electricity
It also costs a lot to melt or dissolve the metal ore so it conducts (ions can move)

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26
Q

Why can carbon only be used to extract metals less reactive than itself

A

Carbon can only take the oxygen (displace) from elements less reactive than iself

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27
Q

Why must ores be molten or dissolved to under go electrolysis

A

So that the ions can move to the electrodes once electric current is passed through

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28
Q

Where is the metal discharged in electrolysis

A

Cathode (negative)

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29
Q

Where is the non-metal discharged in electrolysis

A

Anode (positive)

30
Q

What happens with oxide ions in electrolysis of aluminium oxide

A

They produce oxygen gas which reacted with graphite (carbon) anodes to form CO2 gas

31
Q

Why do anodes need to be replaced at intervals in the electrolysis of aluminium oxide

A

The carbon is used up producing CO2, and the anode gets smaller over time

32
Q

reasons that iron nails are galvanised (coated in zinc)

A
  • zinc is a sacrificial coating
  • zinc prevents oxygen reaching the iron in the nails
  • Its more reactive, so it oxidises in preference to the iron
33
Q

what are some biological methods of extracting metals

A

bioleaching and phytoextraction

34
Q

why may biological methods be used to extract metals from ores

A
  • supply of metal rich ores is limited eg. copper
  • demand for metals is increasing: might lead to future shortages
  • scientists are looking for ways to extract metals from low-grade ores or from waste currently produced when metals are extracted
35
Q

what is a low-grade ore

A

ores that only contain a small percentage of the metal or its compound, it’ll not be as economically viable

36
Q

what is bioleaching

A
  • bacteria breaks energy bonds between atoms in an ore, separating the metal from the ore
  • bacteria produces a solution called leachate which contains the metal compound needed
  • the metal can be extracted from the leachate using displacement with carbon, or electrolysis
37
Q

positives of bioleaching

A
  • more economically viable than just extracting metal from low-grade ores
  • better for the environment
38
Q

negatives of bioleaching

A
  • slow method of extraction
  • still not pure metal: displacement with carbon, or electrolysis still needed
39
Q

what is phytoextraction

A
  • plants grown in soil that contains lowgrade ores
  • metal becomes concentrated in plant tissues
  • plants are dried and burnt in furnaces, metal compounds are found in the ashes
  • metal can be extracted from compound using displacement with carbon, or electrolysis
40
Q

positives of phytomining

A
  • more economically viable than lowgrade ore displacement
  • no heavy machinery needed = better for the environment
41
Q

negatives of phytomining

A

still not pure metal other methods such as displacement with carbon, or electrolysis need to be used to extract the metal

42
Q

what is aluminium oxide dissoved in for electrolysis, and why

A

molten cryolite, because cryolite has a lower melting point (1000°C) than aluminium oxide (2000 °C) therefore it is more economically viable

43
Q

how is the position of a metal in the reactivity series is related to its resistance to oxidation

A
  • more reactive metals (top) lose electrons easily and are also oxidised more easily
  • less reactive metals (bottom) dont lose electrons as easily and are more resistant to oxidation
44
Q

how does recycling conserve resources and energy

A
  • extracting raw materials requires lots of energy (from burning fossil fuels)
  • fossil fuels are finite so need to be conserved
  • recyling uses significantly less energy than extracting new resources
  • raw materials are finite: reusing conserves them
45
Q

how does recycling protect the environment

A
  • mines destroy habitats and ruin the landscape, less mines needed if materials are recycled
  • recycling cuts down on waste sent to landfill, landfill takes up space and pollutes surroundings
46
Q

economic benefits of recycling

A
  • saves money as less energy is used
  • saves money on materials that are expensive to buy or extract
  • large industry: creates jobs (more than is things were just sent to landfill)
47
Q

costs of recycling

A

collection
processing
wages
transport

48
Q

benefits of recycling aluminium

A

for every 1kg recycled:
- 95% energy saved than mining new aluminium
- 4kg aluminium ore saved

49
Q

what do life cycle assessments work out

A

the total environmental impact of a product over the entire period of its life

50
Q

what are the stages of LCA

A
  • obtaining and processing raw materials (choice of material)
  • manufature
  • use of product
  • disposal
51
Q

LCA: obtaining and processing raw materials (choice of material)

A
  • metals have to be mined and extracted (uses lots of energy + causes pollution)
  • raw materials and fossil fuels are finite and extraction and refining use lots of energy + pollute
52
Q

LCA: manufacturing

A
  • uses lots of energy
  • causes pollution (fumes eg. CO)
  • disposal of waste products from manufacture (can it be recycled?)
  • chemical manufacture uses water: don’t put polluted water back in environment after process
53
Q

LCA: use of product

A
  • paint can gice toxic fumes
  • burning fuels releases greenhouse gases
  • fertilisers can leach and damage ecosystems
54
Q

LCA: disposal

A
  • many products disposed at landfill
  • pollutes environment and takes up space
  • air pollution caused by products that are incinerated
55
Q

what does ‘⇌’ mean

A

equilibrium symbol:
the reaction is reversible

56
Q

what is a reversible reaction

A

the reaction may proceed in either direction depending on the conditions
reactants can be made into products and products can be made into reactants

57
Q

what is equilibrium

A
  • when reactants react their conc. fall: foward reaction slows down
  • as conc. of products increases: backward reaction speeds up
  • at equilibrium the foward and backward reactions are happening at the same rate, both reactions are happening but there’s no overall change
58
Q

what is dynamic equilibrium

A

when foward and backward reactions happen at the same time and same rate, and conc. of products and reactants reach a balance and wont change

59
Q

what does it mean when the equilibrium lies to the right

A

conc. of products is greater than the conc. of reactants

60
Q

what does it mean when the equilibrium lies to the left

A

conc. or reactants is greater than the conc. of products

61
Q

what can change the position of equilibrium

A

temperature, pressure (if gases are involved), concentration of products and reactants

62
Q

what is the harber process

A

a reversible reaction: nitrogen and hydrogen react to form ammonia

63
Q

where are the nitrogen and hydrogen gained from for the harber process

A

N2 = air (78% N)
H3 = natural gas

64
Q

method of the harber process

A
  • H and N in a reactor
  • gases are cooled and ammonia turns into a liquid and is removed
  • unreacted H and N recycled, undergo the process again
65
Q

what are the conditions in the reactor for the harber process

A
  • 450°C
  • 200 atmospheres
  • iron catalyst
66
Q

what is the foward reaction in the haber process

A

N2(g) + H3(g) —–> 2NH3 (g) (EXOTHERMIC)

67
Q

what is the backwards reaction in the haber process

A

2NH3 (g) —-> N2(g) + H3(g) (ENDOTHERMIC)

68
Q

what is le chatelier’s principal

A

if there is a change in concentreation, pressure or temperature in a reversible reaction, the equilibrium position will move to help counteract the change

69
Q

le chatelier’s principal: temperature

A
  • all reactions are exothermic in one direction, and endothermic in the other
  • if temperature is decrease, the equilibrium will move in the exothermic direction to produce more heat
  • if it is increased, the equilibrium will move in the endothermic direction to absorb the extra heat
70
Q

le chatelier’s principal: pressure

A
  • only affects equilibria involving gases
  • if presure is increased, equilibrium will move towards the side that has fewer molecules of gas to reduce pressure
  • if pressure is decreased, equilibrium will move towards the side that has more molecules of gas to increase pressure
71
Q

le chatelier’s principal: concentration

A
  • if conc of reactants is increased, equilibrium will move to the right to use up the reactants (make more products)
  • if conc of products in increased, equilibrium will move to left to use up the products (make more reactants)
  • decreasing conc has the opposite effect

GCSE - chemistry (15 decks)

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