Core Knowledge – Topic 4

105) Magnesium produces small bubbles of gas when placed in water; it reacts rapidly with steam and acid. Lithium fizzes on the surface of water. Which is more reactive?

Answer 33
Lithium.

106) What is a displacement reaction?

Answer 106
A redox reaction in which a more reactive element displaces a less reactive element from its compound. Both metals and non-metals take part in displacement reactions.

107) In metal displacement reactions, is the reactive metal oxidised or reduced?

Answer 107
Oxidised.

108) Where are most metals obtained from?

Answer 108
Ores found in the Earth’s crust.

109) Name a metal that is not extracted from an ore and explain why.

Answer 109
Gold because it is so unreactive it doesn’t combine with oxygen in the environment.

110) When metals are extracted are ores oxidised or reduced?

Answer 110
Reduced.

111)Describe how iron is extracted from its ore.

Answer 111
Iron ore (iron oxide) is heated with carbon (the carbon displaces the iron. The iron is reduced – loses its oxygen to the carbon).

112) Describe how aluminium is extracted from its ore.

Answer 112
Aluminium is extracted by electrolysis.

113) Explain why aluminium is extracted in this way, and not by simply heating it with carbon.

Answer 113

Aluminium is a reactive metal.

Reactive metals bond strongly to the other elements in their ores. It requires a lot of energy to break these chemical bonds. Electrolysis can provide large amounts of electrical energy to separate the metal from the other elements in the ore.

All reactive metals have to be extracted by electrolysis. The disadvantage is that this method is expensive.

114) Why is iron not extracted from its ore using electrolysis?

Answer 114
It is cheaper to displace it with carbon.

115) How does the phyto extraction of copper work?

Answer 115
Some plants absorb copper compounds through their roots, the plant is then burnt and the copper extracted from the ash.

116) What is bioleaching?

Answer 116
A method of extracting copper that involves bacteria absorbing copper compounds. The bacteria then produce solutions called leachates which contain copper compounds from which the copper can be extracted.
Answer 116
molecules.

117) Would you expect a metal low down the reactivity series to be susceptible to oxidation?

Answer 117
No, unreactive metals are much less likely to react with oxygen.

118) Why do we recycle scrap metal?

Answer 118

  1. It can often be cheaper to recycle rather than extract new metal from its ore.
  2. Recycling cuts waste which could otherwise harm the environment.
  3. Preserves the remaining raw materials on the planet.

119) What does a lifetime assessment of a product involve?

Answer 33

Evaluating the effect on the environment of:

  1. Manufacturing
  2. Using
  3. Disposing

120) What does this symbol mean? ⇌

Answer 120
It shows a reaction is reversible.

121) What is meant by the term ‘dynamic equilibrium’?

Answer 121
A reversible reaction is said to be in dynamic equilibrium when the rate of the forward reaction is equal to the rate of the backward reaction.

122) How can you change the equilibrium of a reversible reaction?

Answer 122
By changing the conditions, for example temperature and pressure.

123) What is the equation for the Haber process?

Answer 123
N2 (g)   +   3H2 (g)   ⇌   2NH3 (g)

124) Where are the reactants obtained from in the Haber process?

Answer 124
The nitrogen is extracted from air and the hydrogen is obtained from natural gas.

125) What is the chemical formula for ammonia?

Answer 125
NH3

126) What are the conditions used in the Haber process?

Answer 126

  • temperature 450 °C
  • pressure 200 atmospheres
  • iron catalyst

127) How does increasing the temperature affect the yield of ammonia?

Answer 127
The production of ammonia is exothermic so increasing the temperature reduces the yield.

128) If increasing the temperature reduces the yield of ammonia why is a temperature of 450 oC used?

Answer 128
450 oC is a compromise, the temperature is raised to increase the rate of reaction even though it decreases the yield.

129) How does increasing the pressure affect the yield of ammonia?

Answer 129
4 molecules of reactants are needed to make 2 molecules of ammonia. If the pressure is raised more ammonia is produced because that would reduce the number of particles present.

130) How does adding a catalyst affect the yield of ammonia?

Answer 130
It does not affect the yield it just increases the rate.

131) How would the position of a dynamic equilibrium be affected by?

  1. temperature?
  2. pressure?
  3. concentration?
Answer 131

  1. Increasing the temperature will move the dynamic equilibrium in the direction of the endothermic reaction.
  2. Increasing the pressure will move the dynamic equilibrium towards the side where there are less gas molecules.
  3. Increasing the centration of a substance will move the equilibrium to reduce the concentration of that substance.