Find out how everything in a chemistry lab works, from pipettes to burners to recrystallization to storage. You'll get precise instructions on how to work and perform certain scientific duties in the chem lab, whether it's chemical or just ordinary high school science.
Watch this video on how to separate by pipette drawing in the chemistry lab. As an example of how to separate a supernatant from a precipitate with a transfer pipette, the movie explains the separation of iron(III) hydroxide.
This is a simple separation method and especially effective when the precipitate should not be exposed to air. Do not pull out the tip of the transfer pipette from the liquid because air inhalation disturbs the precipitate.
A small amount of the precipitate is always drawn into the pipette along with the supernatant, which can be later removed by filtration. A considerable amount of the liquid is left in the container after pipette drawing. The remaining liquid is transferred by washing the precipitate. Repeating washing with a small amount of the solvent is more effective than washing with a large amount once.
How to Separate a Supernatant from a Precipitate by Pipette Drawing:
- Using a pipette bulb, draw the liquid slowly not to disturb the precipitate.
- Slowly lower the tip of the transfer pipette as the liquid surface goes down.
- Pour a suitable washing solvent to the remaining liquid and precipitate. Transfer the liquid with a pipette. This operation is repeated a few times to wash the precipitate.
- When the supernatant is needed rather than the precipitate, combine the original supernatant and at least the first washing solvent.
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