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Chromatography – Questions With Solutions
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Chromatography – Questions With SolutionsWhat is chromatography? ✔️Ans - An analytical method used to separate
the substances in a mixture.
Used to identify chemicals in a mixture.
What are the two phases required in chromatography? ✔️Ans - - Stationary
phase
- Mobile phase
What is the stationary phase? ✔️Ans - - Where the molecules can't move. It
is a solid or a really thick liquid.
- Fixed in place
Examples of the stationary phase ✔️Ans - - Liquid= in some gas
chromatography (GC) systems, where the mixture components have different
attractions to each phase.
- Solid= In thin layer chromatography, where the components of the mixture
are adsorbed by different amounts.
Example for TLC- thin metal sheet coated in Al2O3 or silica
What is the mobile phase? ✔️Ans - - Where the molecules can move. This is
always a liquid or a gas.
- Moves in a definite direction
- Flows over the stationary phase
- It is a polar or non-polar liquid (solvent) that carries components of the
compound being investigated.
Examples of the mobile phase ✔️Ans - - An inert gas in GC
- A liquid solvent in TLC
-Polar solvents - water or alcohol= TLC
Non-polar solvents - alkanes= TLC
Why does separation in chromatography occur? ✔️Ans - - Because each
chemical in a mixture has different attractions to each phase.
, What substance will travel a long way up the chromatogram? ✔️Ans - - A
substance that is very attracted to the mobile phase, but not the stationary
phase.
What substance will not travel far? ✔️Ans - - A chemical that is very
attracted to the stationary phase.
TLC ✔️Ans - thin layer chromatography
Characteristics of TLC ✔️Ans - - Quick and easy technique
- Can be used to check the purity of a sample or to determine the extent of a
chemical reaction.
Stationary phase of TLC ✔️Ans - - Thin piece of inert material (eg glass)
covered with an absorbent chemical (eg aluminium oxide)
Mobile phase of TLC ✔️Ans - An organic solvent or mixture of solvents
What does the mobile phase do in TLC? ✔️Ans - It will move in one
direction, vertically, up the plate and develop the chromatogram.
What is the Rf value? ✔️Ans - A quantity that shows how far a chemical has
moved up a chromatogram compared to the solvent front.
Rf value ✔️Ans - Distance travelled by substance (component) / distance
travelled by solvent
How does working out the Rf value allow us to identify a substance in a
sample? ✔️Ans - because we can compare that value to Rf values in data
tables.
GC ✔️Ans - Gas chromatography
What is GC used for? ✔️Ans - To separate volatile components in a mixture.
Used for analysing:
- Gases
- Volatile liquids
- Solids in their vapour form
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