Choosing a solvent
- Choose a solvent that the impure substance is NOT soluble in a LOW temperatures but is COMPLETELY soluble in at HIGHER temperatures.
- Add as small amount as possible.
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- Once the solvent has been added to the impure substance, heat the mixture until the impure solid has completely dissolved
- A water bath or bunsen burner could be used for this
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- Cool the solution until crystals have formed
- You could cool it in an ice bath
- If crystals don't form then too much solvent may have been used.
- So allow some of the solvent to evaporate and then heat the solution again and re-cool.
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- Wash the crystals with cold solvent
- Pour the solution/crystals into the Buchner funnel and turn on the vacuum pump.
- The part you want to keep is the solid that hasn't passed through the funnel.
- Dry the solid, this can be just left in the air to dry
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