1. 1
   A fertiliser company manufactures ammonium sulfate, (NH4)2SO4, by reacting ammonia with sulfuric acid. The finished product contains nitrogen, hydrogen, sulfur and oxygen atoms chemically bonded together in a fixed ratio, and is packaged in sealed bags for distribution to farms.

   (a)

   Which term best describes ammonium sulfate?

   [1 mark]

   • AAn element
   • BAn isotope
   • CA mixture
   • DA compound

   (b)

   Which row correctly gives the chemical symbols of the four elements present in ammonium sulfate, (NH4)2SO4?

   [1 mark]

   • ANa, He, Si, O
   • BN, H, S, O
   • CN, He, S, Os
   • DNi, H, Su, O

   (c)

   Explain, in terms of how the atoms are held together, why ammonium sulfate is classed as a compound rather than a mixture of nitrogen, hydrogen, sulfur and oxygen.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A coastal desalination plant takes in seawater, a mixture of water with several dissolved salts. The plant heats the seawater so that pure water evaporates, leaving the dissolved salts behind, then cools the vapour so it condenses and is collected as pure liquid water.

   (a)

   A coastal desalination plant takes in seawater, which contains water with various dissolved salts, and heats it so that pure water evaporates, leaving the salts behind. The water vapour is then cooled and collected as pure liquid water.
   
   Which technique is being used to obtain pure water from seawater?

   [1 mark]

   • AChromatography
   • BFiltration
   • CSimple distillation
   • DCrystallisation

   (b)

   Which statement correctly describes the two changes of state involved in producing pure water from seawater at the desalination plant?

   [1 mark]

   • AThe water freezes, then melts
   • BThe water evaporates, then condenses
   • CThe water sublimes, then deposits
   • DThe water condenses, then evaporates

   (c)

   Explain why simple distillation is a suitable method for separating pure water from the dissolved salts in seawater.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A metal recycling centre receives a container of waste liquid from a factory. The liquid is a mixture of water, dissolved copper sulfate and fine insoluble sand grains, and the workers want to recover the copper sulfate as a solid so it can be resold.

   (a)

   Describe how the workers could obtain a clear solution of copper sulfate, free from the sand.

   [3 marks]

   (b)

   Once the sand has been removed, describe how the recycling centre workers could obtain solid crystals of copper sulfate from the remaining clear solution.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A pharmaceutical manufacturer needs very pure sodium chloride to make saline solution for hospital IV drips. Their starting material is mined rock salt, a mixture of sodium chloride crystals mixed with clay and other insoluble mineral particles.

   (a)

   Describe, in terms of particles and bonding, why the rock salt is a mixture rather than a pure compound, and explain a method the manufacturer could use to obtain pure, dry sodium chloride crystals from it.

   [6 marks]

   (b)

   The manufacturer's quality control team checks the purity of the final sodium chloride by measuring its melting point and comparing it with the known melting point of pure sodium chloride. Evaluate why this melting point test is a suitable way to check purity, and explain why using paper chromatography would not be a practical method for purifying large batches of rock salt.

   [6 marks]

   Total for question 4: 12 marks

End of questions