4. Extracting Metals And Equilibria

Question 1

What are the products when a metal reacts with cold water?

Answer 1

Metal hydroxide and hydrogen gas

Question 2

What are the products when a metal reacts with steam?

Answer 2

Metal oxide and hydrogen gas

Question 3

Write the chemical equation for the reaction that occurs when calcium reacts with cold water

Answer 3

Ca + 2H₂O –> Ca(OH)₂ + H₂

Question 4

Write the chemical equation for the reaction that occurs when zinc reacts with steam

Answer 4

Zn + H₂O –> ZnO + H₂

Question 5

What are the products when a metal reacts with dilute acids?

Answer 5

Salt and hydrogen

Question 6

If a metal reacts with cold water, what does it suggest about the reactivity of this metal?

Answer 6

It suggests the metal is very reactive as only the most reactive metals can react with cold water.

Question 7

A metal reacts with oxygen but not acid or cold water. What does this suggest about the reactivity of this metal?

Answer 7

Not very reactive, most metals react with oxygen.

Question 8

Name a metal which will not react with water, acid, or oxygen

Answer 8

Gold

Question 9

Describe an experiment that uses displacement to compare the reactivity of two metals

Answer 9

Add a solid metal to a salt solution (the salt must contain a different metal).

If the solid metal is more reactive, it will gradually disappear, displacing the metal that was in the salt solution.

If nothing happens, the metal in the salt is more reactive and can’t be displaced.

Question 10

What would you expect to observe when magnesium is added to copper sulfate solution?

Answer 10

The copper sulfate solution is blue.

Magnesium is more reactive than copper so when magnesium is added, the blue solution decolourises and copper coats the surface of the magnesium.

Question 11

Why can a displacement reaction be called a redox reaction? Explain in terms of electron transfer.

Answer 11

A redox reaction occurs when reduction and oxidation are taking place in the same reaction.

In a displacement reaction, the more reactive metal atoms lose electrons to form ions (oxidation) and the less reactive metal ions gain electrons to form the element (reduction).

Question 12

Fill in the gap: ‘The reactivity of a metal is related to its tendency to form _______’

Answer 12

Cations (positive ions)

Question 13

Which metals are most easily oxidised?

Answer 13

The metals highest in the reactivity series. More reactive metals are more likely to react with water and dilute acids to form cations.

Question 14

Where are most metals extracted from?

Answer 14

From ores found in the Earth’s crust.

Question 15

What is an ore?

Answer 15

A rock which contains metals often chemically combined with other substances.

Question 16

Which metals are found in the earth’s crust as uncombined elements?

Answer 16

Unreactive metals

Question 17

Explain what oxidation means in terms of oxygen

Answer 17

Gain of oxygen

Question 18

Explain what reduction means in terms of oxygen

Answer 18

Loss of oxygen

Question 19

Most ores contain metals chemically combined with oxygen. What process must be carried out to extract the metal?

Answer 19

Reduction

Question 20

How can metals be extracted from their ores?

Answer 20

Reduction with carbon: can only be done if the metal is less reactive than carbon (links to reactivity series).

Electrolysis: can be done with all metals, but requires a large amount of energy (high cost).

Question 21

How would you extract iron from its ore?

Answer 21

Iron is less reactive than carbon so can be extracted by reduction with carbon.

Electrolysis could also be used, but this would use a lot of unnecessary energy (high cost).

Question 22

What is the chemical equation for the reduction of iron with carbon?

Answer 22

2Fe₂O₃ + 3C –> 4Fe + 3CO₂

Question 23

How can aluminium be extracted from its ore?

Answer 23

Aluminium is more reactive than carbon so electrolysis must be used.

When the molten ore undergoes electrolysis, the metal forms at the cathode.

Question 24

When aluminium is extracted from aluminium oxide, why is it first dissolved in molten cryolite?

Answer 24

Aluminium oxide has a very high melting point. It is dissolved in molten cryolite to produce an electrolyte with a lower melting point, reducing energy usage and cost.

Question 25

How can plants be used as an alternative metal extraction method? How does it work?

Answer 25

Phytoextraction:
Plants are grown in areas with metals in the soil. The plants take up metals through their roots and concentrate them in their shoots and leaves. These plants are burned and the metals are removed from the ash.

Question 26

How can bacteria be used as an alternative metal extraction method? How does it work?

Answer 26

Bacterial extraction:
Some bacteria absorb metal compounds. These bacteria produce solutions called leachates containing the metals. Scrap iron can be used to remove the metal from the leachate.

Question 27

What are the limitations of biological methods of extraction (bacterial and phytoextraction)?

Answer 27

• Only suitable for low grade ores with smaller quantities of metals.
• Slow processes.
• Require displacement or electrolysis for the final step.

Question 28

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

Answer 28

Oxidation is the loss of electrons. Metals lower in the reactivity series are less reactive. This means that they are less likely to form their cations so are more resistant to oxidation.

Question 29

What are the advantages of recycling metals?

Answer 29

• Economically beneficial because electrolysis is expensive.
• Prevents the detrimental environmental impact of mining and extraction of new metals.
• Less waste produced so less landfill.
• Less energy required compared to electrolysis.
• More sustainable as its not using up the finite resources.
• Recycling process provides employment.

Question 30

What is a life cycle assessment?

Answer 30

Analysis of the overall environment impact that a product may have throughout its lifetime.

Question 31

What different factors does a life cycle assessment of a product consider?

Answer 31

• Extraction and processing of raw materials.
• Manufacturing.
• Packaging and transportation.
• Use of the product.
• Disposal.

Question 32

What is a reversible reaction?

Answer 32

A reaction in which the products can react to form the original reactants.
Donated by the symbol ⇌

Question 33

How can the direction of a reversible reaction be altered?

Answer 33

Changing the reaction conditions.
E.g. temperature, pressure, concentration.

Question 34

What is meant by the term dynamic equilibrium?

Answer 34

Dynamic equilibrium is when the rate of the forward reaction equals the rate of the backwards reaction. This means the concentration of reactants and products are constant even though compounds are continually reacting.

Question 35

What is a closed system?

Answer 35

A system where nothing is added or removed. All reactants and products remain in the reaction vessel.

Question 36

Why is equilibrium only reached if the reaction takes place in a closed system?

Answer 36

The closed system prevents any reactants and products from escaping so that they are able to react continuously.

Question 37

What is the Haber process?

Answer 37

An industrial process used to produce ammonia (for making fertilisers).

Question 38

Write the chemical equation for the reversible reaction between nitrogen and hydrogen, forming ammonia

Answer 38

N₂ + 3H₂ ⇌ 2NH₃

Question 39

Where are the sources of nitrogen and hydrogen for the Haber process?

Answer 39

Nitrogen: extracted from the air.
Hydrogen: obtained from natural gas.

Question 40

TRUE OR FALSE: The process used to form ammonia is a reversible reaction that will never reach dynamic equilibrium.

Answer 40

False - The formation of ammonia is a reversible reaction that will reach dynamic equilibrium in a closed system.

Question 41

What conditions are used for the Haber process?

Answer 41

• 450°C temperature
• 200 atmosphere pressure
• Iron catalyst

Question 42

Explain the effect of increasing the temperature of a reversible reaction if the forward reaction is endothermic.

Answer 42

The forward reaction is endothermic so increasing the temperature favours the forward reaction. The equilibrium will shift towards the forward reaction and the yield of the products will increase.

Question 43

Explain the effect of increasing the pressure of a reversible gaseous reaction.

Answer 43

An increase in pressure will favour the reaction that produces the least number of molecules. The equilibrium position will shift towards the side that produces the fewest gaseous molecules.

Question 44

The equation of the Haber process is N₂ + 3H₂ ⇌ 2NH₃
Explain the effect of increasing the pressure on the yield of ammonia.

Answer 44

Increasing the pressure will shift equilibrium to the right as there are fewer molecules of gas. The yield of ammonia will increase.

Question 45

The concentration of the reactants are increased during a reversible reaction. What effect will this have on the equilibrium position?

Answer 45

The equilibrium will shift to the right so the product yield will increase. This will reduce the effect of the increased concentration of the reactants.

Question 46

If there are equal gaseous molecules of the reactant and product in a reversible reaction, what effect will changing the pressure have on the equilibrium position?

Answer 46

No effect.