1. 1
   A jeweller suspects that a customer's gold ring is not pure gold but an alloy of gold and other metals. To check, the jeweller heats the ring slowly and records the temperature at which it starts to melt and the temperature at which it has fully melted.

   (a)

   A pure gold ring is made of only gold atoms. How should pure gold be classified?

   [1 mark]

   • AElement
   • BCompound
   • CMixture
   • DSolution

   (b)

   If the ring is pure gold, what would the jeweller observe about its melting behaviour, compared with an alloy?

   [1 mark]

   • AIt melts over a range of temperatures, like the alloy
   • BIt melts at one exact, fixed temperature
   • CIt does not melt at all
   • DIt boils before it melts

   (c)

   Explain how the jeweller could use the melting behaviour of the ring to determine whether it is pure gold or a gold alloy.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A forensic scientist is investigating a ransom note and wants to find out which of three suspects' pens was used to write it. The scientist spots a sample of ink from the note, and separate samples of ink from each suspect's pen, onto the same sheet of chromatography paper and allows a solvent to move up the paper.

   (a)

   Which technique is the forensic scientist using to compare the inks?

   [1 mark]

   • ASimple distillation
   • BFiltration
   • CPaper chromatography
   • DCrystallisation

   (b)

   What does the Rf value of a dye spot represent?

   [1 mark]

   • AThe mass of the dye used
   • BThe number of colours in the ink
   • CThe boiling point of the dye
   • DThe ratio of the distance moved by the dye to the distance moved by the solvent

   (c)

   Explain how the forensic scientist could use the Rf values calculated from the chromatogram to identify which suspect's pen was used to write the note.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A chemist has a mixture of two miscible liquids that have different, but reasonably close, boiling points and wants to separate them into their pure components using apparatus consisting of a heated flask, a fractionating column, a thermometer and a condenser.

   (a)

   Describe how fractional distillation could be used to separate a mixture of two miscible liquids with different boiling points.

   [3 marks]

   (b)

   Explain why fractional distillation, rather than simple distillation, is needed to separate this mixture of two liquids with close boiling points, and why the fractionating column improves the separation.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A geologist has a rock sample that is a mixture of sand (insoluble in water) and rock salt (soluble in water). The geologist wants to obtain pure, dry samples of both substances and later confirm that the salt obtained is indeed pure.

   (a)

   Describe a method the geologist could use to do this.

   [6 marks]

   (b)

   Explain how the geologist could use melting point data to confirm that the salt crystals obtained are pure, and explain how the results would differ if the salt were still contaminated with a small amount of sand or another impurity.

   [6 marks]

   Total for question 4: 12 marks

End of questions