2.5d: interpret given information about solvents and solubility to explain the choice of solvents in given contexts, discussing the factors that determine the solubility including: (i) the solubility of ionic compounds in water in terms of the hydration of the ions (ii) the water solubility of simple alcohols in terms of hydrogen bonding (iii) the insolubility of compounds that cannot form hydrogen bonds with water molecules, eg polar molecules such as halogenoalkanes (iv) the solubility in non-aqueous solvents of compounds which have similar intermolecular forces to those in the solvent

Like dissolves with like:

• highly polar solids (eg. NaCl) dissolve in water, which is polar, but not hexane, which is non-polar
• polar organic substances (eg. sucrose) will dissolve in water but not hexane
• non-polar solids (eg. paraffin wax) will dissolve in hexane but not in water
• a polar liquid and a non-polar liquid are immiscible (do not mix) and so will form layers

THE SOLUBILITY OF IONIC COMPOUNDS IN WATER

In an ionic solid, the positive and negative ions are held together by strong electrostatic attraction

Attractive forces between the molecules of water and the ions cause the lattice to be pulled apart

• the water molecules arrange themselves around ions (hydration)

THE WATER SOLUBILITY OF SIMPLE ALCOHOLS

Alcohols are soluble in water because they have polar -OH groups that can form hydrogen bonds with water molecules

• the solubility of alcohols in water decreases as chain length increases

THE INSOLUBILITY OF COMPOUNDS THAT CANNOT FORM HYDROGEN BONDS WITH WATER MOLECULES

THE SOLUBILITY OF NON-AQUEOUS SOLVENTS IN SOLVENTS WITH SIMILAR INTERMOLECULAR FORCES