unit 4 - how to pass: chromatography Flashcards

1
Q

What is chromatography?

A

A technique used to separate the components present within a mixture.

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2
Q

What does chromatography do?

A

It separates substances by making use of differences in their polarity or molecular size.

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3
Q

What does TLC use?

A

A fine film of silica or aluminium oxide spread over glass, aluminium foil or plastic. A small sample of the mixture being tested is spotted onto the base line of the chromatogram. A solvent dissolves the compounds in the sport and carries the compounds up the chromatogram.

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4
Q

What does how far the compounds are carried depend on?

A

How soluble they are in the chosen solvent and how well they adhere to the plate.

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5
Q

What is usually required to visualise the spots on the chromatogram?

A

A developing agent or ultraviolet light.

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6
Q

How can Rf values be calculated?

A

Using the forula: Rf = distance travelled by the sample/distance travelled by the solvent.

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7
Q

When does a compound always have the same Rf value?

A

Under the same conditions (temperature, solvent and saturation levels)

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8
Q

How can the indentity of the compound be confirmed?

A

By comparing the experimentally determined Rf value with a literature or known value determined under the same conditions.

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9
Q

How can a compound also be confirmed?

A

By making a direct comparison on a TLC plate between the compound being tested and the pure substance.

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10
Q

What is TLB used for?

A

To assess the purity of substances.

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11
Q

How should a pure substance, when spotted and developed on a TLC, appear as?

A

A single sport (some impurities may not be visible by TLC analysis).

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12
Q

What shows that impurities are present?

A

The presence of more than one spot.

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