Experimental ChemistryA pure substance…
A mixture..
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Performing chromatography
Pure substance
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Presence of impurities:
Raises the boiling point
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Concept check!
An impure substance of X melts at around 90 °C. What is most likely to be the melting point of X?
between 90 °C to 110 °C
between 80 °C to 90 °C
below 80 °C
cannot be determined
Separation by Magnetic Attraction
Magnets can be used to separate a magnetic metals from a mixture of solids.
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Further Applications of Magnetic Attraction
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23.psd
to separate a dense insoluble solid from liquid
Filtration is better method than decanting
why???
How can you separate a mixture containing salt and sand?
THINK!
filter
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Add some distilled water into the mixture of salt and sand. Stir and make sure all the salt has dissolved.
Filter the mixture.
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 40
No chemical change occurs when salt water is distilled.
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Wash the residue with a little distilled water to remove all the salt solution from it.
Evaporate the filtrate to dryness.
Separating Salt and Sand
Separation Techniques
Separation Techniques
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the process of boiling the liquid and condensing the vapour
Separation Techniques
pure liquid turns into vapour and leaves the flask
vapour is then cooled by a condenser, which changes it back into a liquid
the liquid is collected in the conical flask, and is called the distillate
Separation Techniques
Separation Techniques
methods of purification
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Desalination
disadvantage: expensive method because
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Fractional distillation
to separate mixtures of miscible liquids with widely differing boiling points
Separation Techniques
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How does the temperature change as a solution of ethanol and water undergoes fractional distillation?
Separation Techniques
methods of purification
1. The temperature of the mixture increases as it is heated.
Temperature / oC
Time / s
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How does the temperature change as a solution of ethanol and water undergoes fractional distillation?
Separation Techniques
2. At 78 °C, ethanol distils over.
The temperature remains constant until all the ethanol has distilled out of the round-bottomed flask.
Temperature / oC
Time / s
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How does the temperature change as a solution of ethanol and water undergoes fractional distillation?
Separation Techniques
At 100 °C, water distils over.
The temperature remains unchanged as water is being distilled.
Temperature / oC
Time / s
Fractional distillation
the liquid with the lower boiling point will be distilled first
Separation Techniques
Use of separating funnel
pour the mixture into the separating funnel, ensuring the tap is closed
Separation Techniques
Use of separating funnel
support the separating funnel with a retort stand, placing a clean beaker below it
Separation Techniques
allow some time for the liquids to separate completely
open the tap to allow the denser liquid at the bottom to drain into the beaker
* close the tap before the liquid in the top layer runs out!
Separation Techniques
Use of separating funnel
place another beaker below the separating funnel and allow a little of the liquid in the top layer into it
* dispose this liquid collected
The mixture is separated!
Spin sample very rapidly: denser materials go to bottom (outside)
Separate blood into serum and plasma
Serum (clear)
Blood
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The decomposition of two water molecules. It’s a chemical reaction
2 H2O O2 + 2 H2
Electric
current
Water
molecules
Electrolysis