Topic 4 – Extracting Metals & Equilibria

Question 1

Explain the advantages of recycling aluminium & iron rather than extracting them from their ores (6)

Answer 1

• less power / energy used
—> therefore conserves fossil fuels
• reduces waste in landfill sites
—> so less damage to habitats/landscape
• carbon dioxide is a greenhouse gas
—> greenhouse gases cause global warming
• avoids use of large amounts of electricity to extract aluminium from its ore
—> electricity is expensive

Question 2

Explain why the reaction between metal Y and excess dilute sulfuric acid stopped even though there was solid metal Y left

Answer 2

• metal sulfate insoluble
• prevents further reaction of metal with acid

Question 3

State an advantage of extracting nickel by phytoextraction rather than from its ore

Answer 3

• decontaminates ground / conserves nickel (ores)
• less noise due to mining / less carbon dioxide

Question 4

Describe the experiments that can be done to determine the order of reactivity of these metals (Cu,Mg & Zn) by displacement reactions (3)

Answer 4

• place separate pieces of each metal into solutions of their salt (copper/magnesium/zinc sulfate)
• observe colour change in metal/solution
• the more reactive metal shows the greater number of reactions

Question 5

Devise a simple method to obtain a sample of copper from copper oxide in the laboratory (2)

Answer 5

• react copper oxide with dilute hydrochloric acid
• electrolyse solution formed

Question 6

Explain why aluminum cannot be extracted from its ore by heating with carbon but can be extracted by electrolysis (2)

Answer 6

• aluminum is more reactive than carbon (so electrolysis required)
• carbon cannot displace aluminum
• electrolysis can be used to reduce aluminum ions

Question 7

Explain why electrolysis is used to extract aluminum from its ore

Answer 7

• aluminium is high in the reactivity series / very reactive / more reactive than carbon
• so it requires a lot of energy (to remove oxygen from oxide)

Question 8

Explain why aluminum has to be extracted from its oxide by electrolysis and not by heating its oxide with carbon

Answer 8

• aluminum is high in reactivity
• aluminum (oxide) cannot be reduced by carbon

Question 9

Disadvantages of phytoextraction to extract metals from low-grade ores

Answer 9

• slow process
• large area of land required
• only extracts metal from the ground surface
• metals need further extraction
• harmful/toxic gas released on burning plants

Question 10

Advantages of recycling metals rather than extracting metals from their ores

Answer 10

• reduces waste
• reduces energy needed for metal extraction
• preserves habitats/landscape/resources

Question 11

Metals found in the Earth’s crust as uncombined elements are…

Answer 11

Very unreactive (gold)

Question 12

What type of metals are found in ores?

Answer 12

Reactive metals
(metals are combined with other elements in ores)

Question 13

Stages of life-cycle assessment

Answer 13

• obtaining and processing the raw materials
• manufacturing the product
• using the product
• disposal of the product

Question 14

Advantages of obtaining aluminum by recycling aluminium waste rather than mining the raw material & extracting aluminium from that raw material

Answer 14

• less damage to landscape/habitats
• less pollution/noise
• less energy required
• less waste metal goes into landfill

Question 15

Describe how growing plants can result in phytoextraction of copper

Answer 15

• plants absorb copper/metal ions from soil/ores
• plants are harvested & burned (to leave copper/metal compound)

Question 16

Ca & K react with water in similar ways. One similarity is that hydrogen gas is produced. State one other similarity in the products of the reactions of Ca & K with water

Answer 16

both form a hydroxide

Question 17

State why potassium is higher in the reactivity series & reacts more vigorously with water than calcium

Answer 17

Potassium loses outer electrons:forms cations more easily

Question 18

State why iron can be extracted by heating iron oxide with carbon

Answer 18

Iron is less reactive than carbon

Question 19

State why electrolysis is not used to extract iron

Answer 19

• electrolysis is expensive
• heating with carbon is cheaper
• electrolysis requires a large amount of electricity

Question 20

Advantage of producing a metal by electrolysis

Answer 20

Metal produced is very pure

Question 21

The Haber process is an example of…

Answer 21

A reversible reaction

Question 22

Describe how nitrogen is obtained

Answer 22

From the air (78%)

Question 23

Describe how hydrogen is obtained

Answer 23

Extracted from hydrocarbons from natural gas & crude oil

Question 24

3 conditions for Haber process:

Answer 24

• temperature: 450 degrees Celsius
• pressure: 200 atmospheres
• iron catalyst

Question 25

Explain what is meant by dynamic equilibrium

Answer 25

• forward & backward reactions occur at the same time & at the same rate
• concentrations of reactants + produces are the same, won’t change

Question 26

Explain why equilibrium can only be reached if the reversible reaction takes place in a closed system

Answer 26

• reactants + produces can’t escape
•

Question 27

Le Chatelier’s Principle

Answer 27

if there’s a change in concentration, pressure or temperature in a reversible reaction, the equilibrium position will move to help counteract that change

Question 28

Le Chatelier’s Principle – Temperature

Answer 28

• decreasing temperature
—> equilibrium moves in exothermic direction, to produce more heat

• increasing temperature
—> equilibrium moves in endothermic direction to absorb extra heat.

Question 29

Le Chatelier’s Principle – Pressure

Answer 29

only affects equilibria involving gases
• increase in pressure
—> equilibrium moves towards the side with fewer moles of gas to reduce pressure

• decrease in pressure
—> equilibrium moves towards the side with more moles of gas to increase pressure

Question 30

Le Chatelier’s Principle – Concentration

Answer 30

• increasing concentration of reactants
—> equilibrium moves to the right to use up reactants (making more products)

• increasing concentration of products
—> equilibrium moves to the left to use up products (making more reactants)

• decreasing concentration has opposite effect