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CHEMISTRY > SC4: extracting metals and equilibria > Flashcards

SC4: extracting metals and equilibria Flashcards

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1
Q

the more reactive a metal is…

A

the more vigorous its reactions are
the more easily it loses electrons in reactions to form cations

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2
Q

metal + water

A

metal hydroxide + hydrogen

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3
Q

metals that react quickly with cold water are…?

A

very reactivr

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4
Q

metal + steam

A

metal oxide + hydrogen

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5
Q

how do metals that react slowly with cold water react with steam?

A

quickly

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6
Q

what happens in the reactions of metals with water, steam and acids?

A

-the metals lose electrons and form cations
-the metal is oxidised and the water is reduced

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7
Q

which metals don’t react with dilute acids?

A

metals below hydrogen in the reactivity series

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8
Q

what happens in the reactions of metals with water, steam and acids?

A

-the metals lose electrons and form cations
-the metal is oxidised and the water is reduced
-hydrogen is produced

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9
Q

how does reactivity affect metals tendency to form cations?

A

-the higher up a metal, the more likely to form cations
-the lower down a metal, the more likely to resist oxidation

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10
Q

displacement reaction

A

a reaction in which a more reactive element displaces a less reactive element from an aqueous solution of the latter’s ions

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11
Q

how can the reactivity series be deduced?

A

by doing several displacement reactions; a piece of metal is dipped into a salt solution, different combinations of metal and salt solution are tested

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12
Q

what does it mean if something has been coated in a displacement reaction?

A

the metal reacting with the solution has displaced it

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13
Q

spectator ions

A

ions that do not participate in a reaction

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14
Q

redox reaction

A

an oxidation reaction paired with a reduction reaction

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15
Q

what do metals with a higher reactivity than hydrogen do in displacement reactions?

A

the displace hydrogen from acids

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16
Q

ore

A

a rock that contains enough of a metal or a metal compound to make extracting the metal worthwhile

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17
Q

low grade ores vs high grade ores

A

-low-grade ores = small percentage of the metal or its compound
-high-grade ores contain a larger percentage

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18
Q

how are unreactive metals found?

A

they are found in the earth as the metal itself

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19
Q

why isn’t electrolysis used to extract all metals?

A

large amounts of electrical energy are needed so it’s expensive

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20
Q

how is a metal extracted if it’s less reactive than carbon?

A

heating with carbon

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21
Q

metal oxide + carbon

A

metal + carbon dioxide

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22
Q

extracting iron

A

-as iron is below carbon in the reactivity series it can be displaced from its compounds by heating with carbon
-iron is extracted from iron ore in a a blast furnace
-iron(III) oxide is reduced to molten iron when it reacts with carbon

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23
Q

how are metals higher than carbon extracted?

A

electrolysis

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24
Q

how is impure copper purified?

A

electrolysis

25
Q

what are electrolytes?

A

ionic compounds in the molten state or dissolved in water

26
Q

what are electrodes?

A

charged metal plates

27
Q

cathode

A

negative electrode

28
Q

anode

A

negative electrode

29
Q

what happens at the cathode & anode in electrolysis?

A

cathode: metal ions gain electrons & form an atom

anode: substance loses electrons & forms a gas

30
Q

electrolysis of aluminium oxide

A

-aluminium oxide is insoluble in water, so it must be molten
-the melting point of aluminium oxide is high, a lot of energy must be transferred to break its strong ionic bonds, and this is expensive
-to reduce costs, powdered aluminium oxide is dissolved in molten cryolite
-this ionic compound melts at a lower temperature than aluminium oxide, reducing costs
-both electrodes are made of graphite
-at the cathode, aluminium ions gain electrons and form aluminium atoms
-at the anode, oxide ions lose electrons and form oxygen gas

31
Q

steps of recycling metals

A
  1. collecting and transporting the used items to a recycling centre
  2. breaking up and sorting the different metals
  3. removing impurities from the metals

(the metals can then be used to manufacture new metal items)

32
Q

advantages of recycling metals

A
  1. more economic - less energy is needed to produce a metal
  2. less damage to the environment - fewer quarries and mines, less noise and less heavy traffic
  3. saves valuable raw materials - reserves of metal ores will last longer
33
Q

disadvantages of recycling

A

-the collection and transport of used items needs organisation, workers, vehicles and fuel
-it can be difficult to sort different materials from one another

34
Q

simple way to separate aluminium from iron

A

a magnet or electromagnet will attract iron but not aluminium

35
Q

why is a life cycle assessment (LCA) carried out?

A

carried out to assess the environmental impact of products

36
Q

main stages of a LCA

A
  1. obtaining the raw materials needed for manufacture
  2. manufacturing the product
  3. using the product
  4. disposing of the product at the end of its useful life
37
Q

impact of raw materials (LCA)

A

-using up limited resources such as ores and crude oil
-damaging habitats through quarrying, mining, or felling trees

38
Q

impact of manufacture (LCA)

A

using up land for factories the use of machines and people

39
Q

impact of use (LCA)

A

-the impact of a product on the environment during its use depends on the type of product
-for example, a wooden chair has very little impact, unless it needs cleaning or repair
-on the other hand, a car will have a significant impact

40
Q

impact of disposal (LCA)

A

-using up land for landfill sites
-whether any or all of the product can be recycled or reused

41
Q

phytoextraction steps

A
  1. plants are grown on a low-grade ore that contains lower amounts of metal
  2. the plants absorb metal ions through their roots and concentrate these ions in their cells
  3. the plants are harvested and burnt
  4. the ash left behind contains a higher concentration of the metal than the original ore
  5. the ash is processed to obtain the metal
42
Q

phytoextraction advantages & disadvantages

A

advantages
-reduces the need of mining
-conserves limited supplies of valuable ores

disvantages
-slow

43
Q

quarries

A

-large holes in the ground for mining
-create noise, dust and traffic
-destroy natural habitats

44
Q

biobleaching

A

-certain bacteria can break down low-grade ores to produce an acidic solution (leachate) containing metal ions
-iron is used to displace copper from the leachate
-because iron is cheaper than copper, it’s cost effective

45
Q

biobleaching advantages and disadvantages

A

advantages:
-can extract copper
-doesn’t need high temps
-cost effective

disadvantages:
-produces toxic substances (eg sulfuric acid) which damage the environment

46
Q

reversible reaction

A

the products can be changed back into the reactants

47
Q

dynamic equilibrium

A

-the proportions of reactants and products stay the same
-the term ‘dynamic’ emphasises that the forward and the backward reactions continue to occur (at the same rate)

48
Q

when can dynamic equilibrium happen?

A

in a closed system

49
Q

haber process

A

an industrial process for producing ammonia from nitrogen and hydrogen by combining them under high pressure in the presence of an iron catalyst

50
Q

haber process steps

A
  1. nitrogen (extracted from the air) and hydrogen (obtained from natural gas) are pumped through pipes
  2. a compressor increases the gas pressure to 200 atmospheres
  3. the pressurised gases are heated to
    450°C and passed through a reaction chamber containing an iron catalyst to speed up the reaction
  4. the reaction mixture is cooled so that ammonia liquefies and can be removed
  5. unreacted nitrogen and hydrogen are recycled
51
Q

how can an equilibrium position
be changed?

A

-change temp, pressure or concentration

52
Q

changing pressure in equilibrium

A

if the pressure is increased, the equilibrium position moves in the direction of the fewest molecules of gas

53
Q

changing concentration in equilibrium

A

if the concentration of a solute (thing dissolved) is increased, the equilibrium position moves in the direction away from this solute

54
Q

changing the temperature in equilibrium

A

-in a reversible reaction, if the reaction is exothermic in one direction, it is endothermic in the other direction
-if the temperature is increased, the equilibrium position moves in the direction of the endothermic process

55
Q

exothermic

A

releases energy/heat

56
Q

endothermic

A

absorbs heat/energy

57
Q

what does the temp used in a
reversible reactions depend on?

A

-low enough to get an acceptable yield
-high enough to do this in an acceptable time

58
Q

what does pressure used in reversible reactions depend on?

A

-low enough to keep costs down
-high enough for achievable yield

CHEMISTRY (9 decks)

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