Industrial processesIB MYP Chemistry: Subtopic test

1. 1
   Ammonia is made on a large scale in the Haber process. Nitrogen from the air reacts with hydrogen at about 450 °C and 200 atmospheres pressure, over an iron catalyst: N₂ + 3H₂ ⇌ 2NH₃. The mixture leaving the reactor contains ammonia, nitrogen and hydrogen.

   (a)

   What does the symbol ⇌ in the equation show?

   [1 mark]

   • AThe reaction goes to completion
   • BThe reaction can go in both directions
   • CThe reaction needs a catalyst
   • DThe reaction releases heat

   (b)

   What is the role of the iron in the Haber process?

   [1 mark]

   • AIt is a reactant that is used up
   • BIt increases the percentage of ammonia at equilibrium
   • CIt is a product of the reaction
   • DIt speeds up the reaction and is not used up

   (c)

   Explain why the unreacted nitrogen and hydrogen leaving the reactor are recycled.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A fertiliser factory in Brazil uses ammonia from the Haber process to make ammonium nitrate, NH₄NO₃, which is sold to farmers who grow maize.

   (a)

   Which element in ammonium nitrate is most important for helping maize plants to grow?

   [1 mark]

   • ANitrogen
   • BOxygen
   • CHydrogen
   • DCalcium

   (b)

   The factory makes ammonium nitrate by reacting ammonia with nitric acid. What type of reaction is this?

   [1 mark]

   • ACombustion
   • BDisplacement
   • CNeutralisation
   • DDecomposition

   (c)

   Explain why farmers add nitrogen fertilisers to the soil.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Sulfuric acid is made on a large scale by the Contact process. Sulfur is burned in air to make sulfur dioxide. The sulfur dioxide is then converted to sulfur trioxide, SO₃, in a reversible reaction using a vanadium(V) oxide catalyst at about 450 °C. Finally the sulfur trioxide is absorbed to make concentrated sulfuric acid.

   (a)

   Write balanced symbol equations for the burning of sulfur and for the conversion of sulfur dioxide to sulfur trioxide.

   [3 marks]

   (b)

   The conversion of sulfur dioxide to sulfur trioxide gives the highest percentage of sulfur trioxide at low temperatures, but it is slow. Explain why the temperature chosen is about 450 °C and why a catalyst is used.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A chemical company is planning a new ammonia plant in Kenya to supply nitrogen fertiliser to local farmers. Engineers carry out trials of the Haber process with an iron catalyst. At a pressure of 200 atmospheres: at 350 °C, 40% of the mixture is ammonia and it takes 40 hours to reach equilibrium; at 450 °C, 18% and 8 hours; at 550 °C, 8% and 2 hours. At 450 °C: at 100 atmospheres 10% of the mixture is ammonia, at 200 atmospheres 18%, and at 400 atmospheres 30%.

   (a)

   Describe the trends in the data and use them to evaluate the choice of 450 °C and 200 atmospheres for the plant.

   [6 marks]

   (b)

   Discuss and evaluate the company's plan to build the ammonia plant to supply nitrogen fertiliser to farmers.

   [6 marks]

   Total for question 4: 12 marks

End of questions