1. 1
   A chemical engineer at an ammonia (Haber process) plant uses iron as a catalyst to speed up the reaction between nitrogen and hydrogen. She notices that a very dense metal is used for the reactor casing and catalyst pellets.

   (a)

   Which property of iron makes it useful as a catalyst in the Haber process?

   [1 mark]

   • AIt speeds up the reaction without being used up
   • BIt has a low melting point
   • CIt reacts vigorously with cold water
   • DIt is a poor conductor of heat

   (b)

   Which of the following is a general physical property of transition elements such as iron?

   [1 mark]

   • ALow density
   • BHigh density
   • CForms colourless compounds only
   • DFull outer shell of electrons

   (c)

   State two general properties of transition elements, other than high density.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A jewellery designer selects gemstones and metal alloys for a new collection. She notices that compounds containing copper give a blue-green colour to some of the stones, while pure iron and nickel are used to make strong, hard-wearing rings.

   (a)

   Which type of element forms compounds that are often coloured, such as the blue-green copper compounds used in the gemstones?

   [1 mark]

   • AGroup I metals
   • BNoble gases
   • CTransition elements
   • DNon-metals

   (b)

   Which statement about transition elements is correct?

   [1 mark]

   • AThey form ions with only one oxidation number
   • BThey are unreactive gases
   • CThey have low melting points
   • DThey form ions with variable oxidation numbers, such as iron(II) and iron(III)

   (c)

   Iron can form compounds containing iron(II) ions or iron(III) ions. Explain what is meant by 'variable oxidation numbers' and give this example.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A doctor prescribes iron supplements to a patient with anaemia. The supplements contain iron(II) sulfate, but when exposed to air for a long time some of the iron(II) compound changes into an iron(III) compound, changing the colour of the tablets from pale green to brown.

   (a)

   Explain, in terms of oxidation numbers, why the change from iron(II) sulfate to an iron(III) compound shows that iron is a transition element.

   [3 marks]

   (b)

   Suggest why the colour change described (pale green to brown) is expected for a transition element compound, and describe two other general properties of transition elements that would not be shown by a Group I metal compound in the same tablets.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A historian researching the industrial revolution studies old factory records describing the use of iron and iron catalysts in various chemical industries, alongside decorative brass and bronze fittings made from copper alloys.

   (a)

   Using the information about iron and the general properties of transition elements, describe how transition elements differ from Group I metals in terms of density, melting point, hardness and reactivity with cold water.

   [6 marks]

   (b)

   Explain why transition elements such as iron and copper are useful in industry, referring to their properties as catalysts, their variable oxidation numbers, and their physical properties.

   [6 marks]

   Total for question 4: 12 marks

End of questions