Recrystallisation

The solvent in recrystallisation should be such that _____. Tick all that apply.

• the compound being purified is completely soluble at high T

• the compound being purified is completely soluble at low T

• the compound being purified is only sparingly soluble at high T

• the compound being purified is only sparingly soluble at low T

Step 1 of Recrystallisation: Dissolve ____ solid gently in a _____ volume of hot solvent.

• pure; minimum

• pure; maximum

• impure; minimum

• impure; maximum

Step 2 of Recrystallisation: Hot filtration of the resulting mixture to remove any _____ impurities.

• soluble

• insoluble

Step 3 of Recrystallisation: Cool the filtrate _____ to allow crystals of the pure compound to form, leaving soluble impurities dissolved in the solvent.

• slowly

• quickly

Step 4 of Recrystallisation: _____. Tick all that apply.

• Filtering the crystals

• Washing the crystals

• Drying the crystals

The purpose of scratching the glass is to

• provide a nucleus for the impurities to attract to

• provide a nucleus for the crystals to form

• cool the mixture

Name an appropriate organic solvent

(a)  

We can check the purity of the solid by its

• boiling point

• smell

• melting point

• crystallisation point

Repeated crystallisations could be carried out. What effect will this have?

• Increased solubility

• Increased purity

• Increased yield

• Decreased yield