Question 3
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- Give the reason why organic substances are usually recrystallized after they have been produced.
- Outline how recrystallization could be carried out in the laboratory.
- State two pieces of apparatus required for the evaporation of sodium chloride Solution to dryness.
Observation
Majority of the candidates responded to this question. However, their performance was below average
In part (a), majority of the candidates could not give the reason why organic substances are usually recrystallized. Also, they could not outline how recrystallization could be carried out in the laboratory.
In part (b), majority of the candidates were able to state the apparatus required for the evaporation of sodium chloride to dryness. However, some candidates that mentioned tripod stand left out wire gauze. This resulted in loss of marks.
The expected answers include:
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- To purify the sample
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- Put sample in a beaker, and add a suitable solvent
- Heat mixture to dissolve the sample
- The solution obtained is filtered while hot
- The filtrate is partially evaporated and cooled to form crystals
- The resulting crystals are filtered and then dried
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- Evaporating dish/beaker
- Bunsen burner/mentioned source of heat
- Tripod stand with wire gauze
- Stirring rod/glass rod.