Topic 4 - Extracting Metals And Equilibria

Question 1

How can you deduce the reactivity of metals by reacting them with acids?

Answer 1

You can place little pieces of various metals of same size into dilute hydrochloric acid.

• Magnesium will make a loud squeaky pop (Most Reactive)
• Aluminium will make a fair squeaky pop
• Zinc will make a quiet squeaky pop
• Iron will make a very quiet squeaky pop
• Copper will not make a sound (Least reactive)

Question 2

How can you deduce the reactivity of metals by reacting them with water? (6)

Answer 2

Place metal pieces in water
Fast reaction with cold water: Potassium, Sodium
Slow reaction with cold water: Calcium, Magnesium
Usually no reaction: Aluminium, Zinc
Rusts slowly: Iron
Definitely no reaction: Copper, Silver, Gold

Question 3

How can you deduce the reactivity of metals by reacting them with salt solutions?

Answer 3

A more reactive metal can displace a less reactive metal from its compounds. For example, magnesium is more reactive than copper. It displaces copper from copper sulfate solution (salt).

magnesium + copper sulfate → magnesium sulfate + copper

Question 4

Why are displacement reactions known as redox reactions?

Answer 4

Reduction and oxidation happen at the same time, so displacement reactions are called redox reactions.

E.G:
Mg(s) + Cu2+(aq) → Mg2+(aq) + Cu(s)

This equation is an example of a balanced ionic equation. It can be split into two half equations:

Mg(s) → Mg2+(aq) + 2e- (oxidation)

Cu2+(aq) + 2e- → Cu(s) (reduction)

Notice that:
magnesium atoms lose electrons - they are oxidised
copper ions gain electrons - they are reduced

Question 5

What are the most reactive metals likely to form?

Answer 5

Cations as they lose their electrons more easily.

Question 6

What is a metal ore?

Answer 6

A rock which contains enough metal to make it economically worthwhile extracting metal from it. In many cases the ore is an oxide of an metal.

Question 7

Where are most metals obtained from?

Answer 7

Most metals that we use are found in their ores in the Earth’s crust. The ores are mined and the metals can be extracted.

Question 8

How are unreactive metals found?

Answer 8

Some unreactive metals, such as gold and platinum, are present in the Earth’s crust as uncombined elements. These metals can be mined straight out of the ground, but they usually need to be refined before they can be used.

Question 9

What is oxidation and reduction?

Answer 9

Oxidation is the gain of oxygen by a substance

Reduction is the loss of oxygen by a substance

Question 10

How are metals higher than carbon in the reactivity series extracted?

Answer 10

Electrolysis - Potassium, sodium, calcium, magnesium and aluminium.

Question 11

How are metals below carbon extracted?

Answer 11

Reduction using carbon. Iron oxide is reduced in a blast furnace to make iron. This is because carbon can only take the oxygen away from metals which is less reactive than carbon itself is.

Question 12

Describe the preparation for the electrolysis of Aluminium oxide to get Aluminium.

Answer 12

Aluminium oxide is insoluble in water, so it must be molten to act as an electrolyte. However, 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.

Question 13

Describe the electrolysis of Aluminium oxide to get Aluminium

Answer 13

At the cathode, aluminium ions gain electrons and form aluminium atoms
At the anode, oxide ions lose electrons and form oxygen gas

The oxygen reacts with the carbon anodes, forming carbon dioxide. So the anodes gradually wear away. They must be replaced frequently, adding to the cost of producing aluminium.

Question 14

Why is Electrolysis more expensive than reduction with carbon? (3)

Answer 14

Lots of electricity is need which is very expensive. You have to melt/ dissolve the metal ore so it can conduct electricity. Whereas carbon is cheap and also acts as a fuel to provide the heat need for the reduction reaction to happen.

Question 15

Describe the alternative bacterial method of extracting metals. (4)

Answer 15

Certain bacteria can break down low-grade ores to produce an acidic solution containing metal ions. The solution is called a leachate and the process is called bioleaching.

Bioleaching can be used to extract copper metal. It does not need high temperatures, but it produces toxic substances, including sulfuric acid, which damage the environment.

Question 16

Describe the alternative biological method of extracting method - Phytoextraction. (6)

Answer 16

Plants absorb mineral ions through their roots. Phytoextraction makes use of this to extract metals:

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

Question 17

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

Answer 17

The less reactive metals are more resistant to oxidation than more reactive metals.

Question 18

What are the advantages of recycling metals? (3)

Answer 18

• More economic - less energy is needed to produce a metal
• Less damage to the environment - fewer quarries and mines, less noise and less heavy traffic
• Saves valuable raw materials - reserves of metal ores will last longer

Question 19

What are the disadvantages of recycling metals? (2)

Answer 19

• The collection and transport of used items needs organisation, workers, vehicles and fuel
• It can be difficult to sort different materials from one another

Question 20

What is a Life-cycle Assessment and what are its main stages? (5)

Answer 20

A life-cycle assessment or LCA is a ‘cradle to grave’ analysis of the impact of a manufactured product on the environment. The main stages are:

1) obtaining the raw materials needed
2) manufacturing the product
3) using the product
4) disposing of the product at the end of its useful life

Question 21

Describe the first stage of a Life-cyle Assessment - Raw materials. (3)

Answer 21

All the raw materials we need come from the Earth’s crust, atmosphere or oceans, or are due to living organisms. Obtaining these materials has an impact on the environment, including:

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

Question 22

Describe the second stage of a Life-cycle Assessment - Manufacture. (2)

Answer 22

The manufacture of products has an impact on the environment, including:

• using up land for factories
• the use of machines and people

Question 23

Describe the third stage of a Life-cycle Assessment - Use

Answer 23

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.

Question 24

Describe the fourth stage of a Life-Cycle Assessment - Disposal. (2)

Answer 24

The disposal of old products has an impact on the environment, including:

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

Question 25

Describe reversible reactions. (3)

Answer 25

This means that the products can be changed back into the original reactants. Chemical reactions are reversible and may reach a dynamic equilibrium. The direction of reversible reactions can be altered by changing the reaction conditions.

Question 26

What is dynamic equilibrium? (4)

Answer 26

When a reversible reaction happens in a closed container, it can achieve a dynamic equilibrium. At equilibrium:

• the forward and backward reactions are still happening
• the rates of the forward and backward reactions are the same
• the concentrations of the reactants and products remain constant (they do not change)

Question 27

Describe what ammonia is used and how it is formed.

Answer 27

Ammonia is an important industrial product used to make fertilisers, explosives and dyes. It is manufactured using the Haber process. This involves a reversible reaction between nitrogen and hydrogen:

N2(g) + 3H2(g) ⇌ 2NH3(g)

The reaction can reach a dynamic equilibrium.

Question 28

Describe the Haber Process. (5)

Answer 28

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

Question 29

Describe the conditions for the Haber process

Answer 29

• 450˚c
• 200 ATMOSPHERES
• IRON catalyst

Question 30

Why is the Haber process conducted at 450˚c?

Answer 30

A low temperature is needed for this reaction so the equilibrium will move in the exothermic direction to increase the heat therefore making more ammonia which improves the productivity of the Haber process. However, the rate of reaction becomes too slow at very low temperatures so a compromise temperature of 450˚c is used as is low enough to achieve an acceptable yield of ammonia and high enough to create this amount of ammonia in an acceptable time.

Question 31

Why is the Haber process conducted at 200 atmospheres?

Answer 31

A higher pressure means that the equilibrium will shift to the right which the side of the fewest moles to decrease pressure which is also the side that increases the production of ammonia. However, it is expensive to achieve high pressures as more energy and stronger equipment is needed so a compromise pressure is used to keep costs low and get an acceptable yield.

Question 32

How is the position of equilibrium affected by pressure?

Answer 32

In a reaction involving gases, if the pressure is increased, the equilibrium position moves in the direction of the fewest moles of gas to decrease pressure.

If the pressure is decreased, the equilibrium position moves in the direction of the most moles of gas to increase the pressure.

Question 33

How is the position of equilibrium affected by temperature?

Answer 33

If the temperature is increased, the equilibrium position moves in the direction of the endothermic process to absorb the extra heat (decrease temperature).

If the temperature is decreased, the equilibrium position moves in the direction of the exothermic process to produce more heat (increase temperature).

Question 34

How is the position of equilibrium affected by concentration?

Answer 34

If the concentration of a reactant is increased the equilibrium will shift in the direction of the reaction that uses the reactants, so that the reactant concentration decreases. The forward reaction is favoured.

The forward reaction is also favoured if the concentration of the product is decreased, so that more product is formed.

If the concentration of a reactant is decreased the equilibrium will shift in the direction of the reaction that produces the reactants, so that the reactant concentration increases. The reverse reaction is favoured.

The reverse reaction is also favoured if the concentration of the product is increased, so that product is used.