Solvents and solubilityEdexcel International A Level Chemistry: Subtopic test

1. 1
   Sodium chloride is a white ionic solid. It dissolves readily in water but is insoluble in hexane, C₆H₁₄, which is a non-polar liquid.

   (a)

   Which term describes the process in which water molecules surround the ions of a dissolved salt?

   [1 mark]

   • AHydration
   • BHydrolysis
   • CDehydration
   • DNeutralisation

   (b)

   Which statement best explains why sodium chloride is insoluble in hexane?

   [1 mark]

   • AHexane molecules are polar and repel the ions
   • BHexane molecules are non-polar so cannot attract the ions strongly enough to overcome the ionic lattice
   • CHexane forms hydrogen bonds that are too strong
   • DHexane is less dense than sodium chloride

   (c)

   Explain how water dissolves sodium chloride.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Ethanol, CH₃CH₂OH, mixes completely with water. 1-Chlorobutane, CH₃CH₂CH₂CH₂Cl, is a polar liquid but is only very slightly soluble in water.

   (a)

   Which feature of an ethanol molecule allows it to form hydrogen bonds with water molecules?

   [1 mark]

   • AThe C–C bond
   • BThe ethyl group, CH₃CH₂–
   • CThe O–H group
   • DThe hydrocarbon chain as a whole

   (b)

   Which statement best explains why 1-chlorobutane is only slightly soluble in water?

   [1 mark]

   • AIts molecules are non-polar
   • BIt is too dense to mix with water
   • CIt forms strong hydrogen bonds with itself
   • DIt cannot form hydrogen bonds with water, and the attractions it can form are weaker than the hydrogen bonds between water molecules

   (c)

   Explain, in terms of intermolecular forces, why ethanol mixes completely with water.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A technician is choosing solvents. Water is a polar liquid whose molecules are held together by hydrogen bonds. Hexane is a non-polar liquid whose molecules are held together only by London forces. 1-Bromobutane, CH₃CH₂CH₂CH₂Br, is a polar molecule that cannot form hydrogen bonds.

   (a)

   Explain why 1-bromobutane is only slightly soluble in water.

   [3 marks]

   (b)

   Predict, with a reason in each case, which solvent, water or hexane, would be better for dissolving (i) potassium bromide, KBr, and (ii) hexadecane, C₁₆H₃₄, a non-polar liquid.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student investigates the solubility of two substances in two solvents. The substances are sodium chloride and octane, C₈H₁₈, a non-polar liquid. The solvents are water and hexane, C₆H₁₄, a non-polar liquid.

   (a)

   Explain why sodium chloride dissolves in water but not in hexane.

   [6 marks]

   (b)

   Explain why octane is insoluble in water but dissolves in hexane.

   [6 marks]

   Total for question 4: 12 marks

End of questions