extracting metals and equilibria

Question 1

what do the two arrows over each other going in opposite directions show us

Answer 1

• the reaction goes both ways

Question 2

how can the direction of some reversible reactions be altered

Answer 2

by changing the reaction conditions

Question 3

chemical reaction can be

Answer 3

reversed

Question 4

what is meant by dynamic equilibrium

Answer 4

• when the rate of the forward reaction is equal to the rate of the backward reaction
• at dynamic equilibrium the concentration of reactants and products remains constant

Question 5

describe the formation of ammonia

Answer 5

• a reversible reaction
  -> between nitrogen (extracted from air) and hydrogen (obtained from natural gas)
  -» that can reach a dynamic equilibrium

Question 6

recall the conditions for that Haber process carried out as

Answer 6

• temp 450 degrees
• pressure 200 atmospheres
• iron catalyst

Question 7

predict how the position of dynamic equilibrium is affected by changes in temperature

Answer 7

• decrease the temperature and the equilibrium will move in the exothermic direction to produce more heat
• increasing the temperature makes the equilibrium move in the endothermic direction to absorb extra heat

Question 8

predict how the position of dynamic equilibrium is affected by changes in pressure (only affects equilibria in gases)

Answer 8

• increase pressure = equilibria moves towards the side that has fewer moles of gas to reduce pressure
• decrease pressure = the equilibria will move towards the side that has more moles of gas to increase pressure

Question 9

predict how the position of dynamic equilibrium is affected by changes in concentration

Answer 9

• increase concentration of reactants = equilibria will move to the right to use up the reactant (making more products)
• increase concentration of products = equilibrium will move to the left to use up the products (making more reactants)
• decreasing concentration has the opposite effect

Question 10

Deduce the relative reactivity of some metals, by their reactions
with water

Answer 10

• more reactive elements (potassium, sodium, lithium, calcium) react a lot with water
• less reactive elements (magnesium, zinc, iron) react less with water (react with steam)
• copper does not react with water or steam

Question 11

Deduce the relative reactivity of some metals, by their reactions
with acids and salt solutions

Answer 11

• more reactive metal means faster reaction will go with acid

Question 12

Explain displacement reactions as redox reactions, in
terms of gain or loss of electrons

Answer 12

• more reactive element reacts to take place of less reactive element
• more reactive metal is oxidised and less reactive metal is reduced

Question 13

explain the reactivity series of metals in terms of the reactivity of the metals with water and dilute acids and that these reactions show the relative tendency of metal atoms to form cations

Answer 13

• metals at top of series are most reactive and lose their electrons to form cations (+), oxidised easily
• metals at bottom are less reactive and are harder to form cations, more resistant to oxidation

Question 14

where are most metals extracted from

Answer 14

ores found in the earth’s crust

Question 15

where are unreactive metals found

Answer 15

in the earth’s crust as the uncombined elements

Question 16

oxidation is

Answer 16

gain of electrons

Question 17

reduction is

Answer 17

loss of electrons

Question 18

what does the extraction of metals involve

Answer 18

reduction of ores

Question 19

explain why the method used to extract a metal from its ore is
related to its position in the reactivity series and the cost of the
extraction process, illustrated by
a. heating with carbon (including iron)

Answer 19

• metals higher than carbon are extracted with electrolysis = expensive
• metals below carbon are extracted by reduction using carbon
  -> as carbon can only take oxygen away from metals which are less reactive than carbon itself

Question 20

what is the bacterial method of extraction

Answer 20

• bioleaching
• uses bacteria to separate metals from their ores

Question 21

what is the phytoextraction method of extraction

Answer 21

• uses plants in soil which contain metal compounds

Question 22

explain bacterial/ bioleaching method of extraction

Answer 22

• uses bacteria to separate metals from their ores
• bacteria get energy from bonds between atoms in the ore so separating out the metal from the ore
• the leachate (solution produced by the process) contains metal ions which can be extracted
  -> ex by electrolysis or displacement with a more reactive metal

Question 23

explain the phytoextraction method of metal extraction

Answer 23

• involves growing plants in soil which contains metal compounds
• plants metals builds up in the leaves
• plants are harvested, dried then burned
• ash contains metal compounds which metal can be extracted from
  -> using electrolysis or displacement reactions

Question 24

evaluate alternative biological methods of metal extraction (bacterial and phytoextraction)

Answer 24

• less damaging to environment (reduces mining)
• slower
• bioleaching can produce toxic substances

Question 25

Explain how a metal’s relative resistance to oxidation is related to its position in the reactivity series

Answer 25

- bottom of series means more resistant to oxidation -> because they don't give up their electrons to form cations as easily

Question 26

advantages of recycling metals

Answer 26

- less energy needed to produce a metal = more economic - less damaging to environment (fewer mines) - saves valuable raw materials (reserves of metal ores will last longer)

Question 27

what is a life cycle assessment

Answer 27

impact of a manufactured product on the environment

Question 28

stages of the life cycle assessment

Answer 28

1. obtaining raw materials 2. manufacturing product 3. using product 4. disposing product once not useful

Question 29

explain the impacts to the environment of the stages of the life cycle assessment

Answer 29

1. raw materials - using up limiting resources like ores and crude oil, damages habitats 2. manufacture - using up land for factories, use of machines and people 3. use - depends 4. disposal - using up land for landfill, whether product can be recycled or reused

Question 30

evaluate data from a life cycle assessment of a product

Answer 30

see which are more harmful to environment