Topic 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

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

Answer 3

Salt and hydrogen

Question 4

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

Answer 4

It is very reactive

Question 5

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

Answer 5

Not very reactive, most metal react with oxygen

Question 6

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

Answer 6

Gold

Question 7

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

Answer 7

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 cannot be displaced

Question 8

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

Answer 8

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 9

What is the reactivity of a metal related to its tendency to form?

Answer 9

Cations

Question 10

Which metals are most easily oxidised?

Answer 10

The ones highest in the reactivity series.

Question 11

Where are most metals extracted from?

Answer 11

From ores forums in the earth’s crust

Question 12

What is an ore?

Answer 12

A rock which contains metals often chemically combined with other substances

Question 13

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

Answer 13

Unreactive metals

Question 14

Explain what oxidation means in terms of oxygen

Answer 14

Gain of oxygen

Question 15

Explain what reduction means in terms of oxygen

Answer 15

Loss of oxygen

Question 16

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

Answer 16

Reduction

Question 17

Which two methods could be used to extract metals from their ores?

Answer 17

Reduction with carbon

Electrolysis

Question 18

How would you extract iron from its ore?

Answer 18

Iron is less reactive than carbon so can be extracted by reduction with the carbon
Electrolysis could also be used, but this would use a lot of unnecessary energy

Question 19

How can aluminium be extracted from its ore?

Answer 19

Aluminium is more reaction than carbon so electrolysis must be used
When the molten ore undergoes electrolysis, the metal forms at the cathode

Question 20

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

Answer 20

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 21

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

Answer 21

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

Question 22

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

Answer 22

Bacteria 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 23

What are the limitations of biological methods of extraction?

Answer 23

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

Question 24

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

Answer 24

Metals lower in the reactivity series are less reactive. This means they are less likely to form their cations so are more resistant to oxidation

Question 25

What are the advantages of recycling metals?

Answer 25

Prevents detrimental environmental impact of mining and extraction of new metals
Less waste produced so less landfill
Less energy required compared to electrolysis
More sustainable
The process provides employment

Question 26

What is a life cycle assessment?

Answer 26

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

Question 27

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

Answer 27

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

Question 28

What is a reversible reaction?

Answer 28

A reaction in which the products can react to form the original reactants

Question 29

How can the direction of a reversible reaction be altered?

Answer 29

Changing the reaction conditions

Question 30

What is meant by the term dynamic equilibrium?

Answer 30

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 31

What is a closed system?

Answer 31

A system where nothing is added or removed

All reactants and products remain in the reaction vessel

Question 32

Why is equilibrium only reached if the reaction take solace in a close system?

Answer 32

It prevents any reactants and products escaping so that they are able to react continuously

Question 33

What is the Haber process?

Answer 33

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

Question 34

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

Answer 34

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

Question 35

Is the formation of ammonia a reversible reaction?

Answer 35

Yes, it will reach dynamic equilibrium in a closed system

Question 36

What conditions are used for the Haber process?

Answer 36

450°C temperature
200 at, pressure
Iron catalyst

Question 37

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

Answer 37

It favours the forward reaction so the yield of th products will increase

Question 38

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

Answer 38

It will favour the reaction that produces the least number of molecules

Question 39

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

Answer 39

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

Question 40

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 40

No effect