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Chemistry (A2) > Chromatography > Flashcards

Chromatography Flashcards

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1
Q

What is the Mobile phase?

A

Solvent that caries the soluble components of the mixture

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2
Q

If a sample moves faster then another.
How does the relationship between the phases differ?

A

The sample that moves faster has a stronger affinity for the mobile phase.

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3
Q

If a sample moves slower then another.
How does the relationship between the phases differ?

A

The sample that moves slower has a stronger affinity for the stationary phase.

-usually components are hydrogen bonded to the stationary phase

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4
Q

What is the Stationary phase?

A

A medium that attracts the components in the mixture, resisting motion against the mobile phase

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5
Q

How are substances separated by chromatography? (3)

A
  • Suitable stationary & mobile phases are choses
  • The balance between affinity for the mobile and stationary phases is different for each component in the mixture
  • Different components move at different rates, and are separated from one another over time
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6
Q

Why will different substances show different Rf Values?
Explain why the differences occur (3)

A
  • All Molecules are bonded differently & have different polarities
    -More polar bonds gives more affinity to the stationary phase and a smaller Rf Value
    -Hydrogen bonding and dipoles are attracted more strongly to the stationary phase
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7
Q

What does TLC stand for?

What is the Stationary phase?

What is the Mobile Phase?

A

Thin Layer Chromatography

Glass, plastic or metal plate coated in silica (SiO2), alumina (Al2O3) or both.

Mobile phase dependant on the possible components of the micxture

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8
Q

What are the advantages of TLC over Paper Chromatography?

A

Runs Faster.

Smaller amounts of mixture can be separated

Plates are more robust then paper

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9
Q

How do you analyse the results of TLC via UV Light? (4)

A

-Add fluorescent dye to silica/alumina
-Shine UV light onto plate
-Colourless spots on the chromatogram will block any glow from the fluorescent dye
-Draw round the spots to mark where they are

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10
Q

How do you analyse the results of TLC via Iodine? (2)

A
  • Place chromatogram in a sealed jar with iodine crystals
    -Iodine vapour (locating agent) sticks to the colourless spots turning them purple
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11
Q

How do you analyse the results of TLC via Ninhydrin? (2)
What can Ninhydrin analyse?

A

-Spray chromatogram with heated ninhydrin (developing agent)
-Ninhydrin turns amino acid spots from colourless to purple

-Amino acids

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12
Q

How do you calculate Rf Values

A

Distance moved by spot / distance travelled by solvent front
Both measured from the baseline

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13
Q

What is an Rf Value?

A

Retention Factor

A ratio of the rate of movement between the solvent and components within the mixture

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14
Q

How do you confirm the identity of a substance from an Rf value? (2)

A

-Compare the Rf Value to accepted values of Rf for that substance
- make sure the Rf for the accepted value is the same solvent and set up as your own

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15
Q

What is Column Chromatography? (4)

A

A glass column pack with silica or alumina which acts as the stationary phase

The mixture and solvent (mobile phase) is run through the column continuously

Different compounds in the mixture run through the column at different rates - producing different retention times

Each pure separated component can be collected separately at different intervals

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16
Q

What is the mobile phase in Column Chromatography?

A

Solvent that is added to the top and runs down the column
- Called Eluent

17
Q

What is the stationary phase in Column Chromatography?

A

Silica Alumina or resin packed into a glass column

18
Q

Draw a Diagram of Column Chromatography

A
19
Q

What are the Advantages of Column Chromatography?

A

More then one eluent can be used - leads to better separation then TLC

Large amounts of mixture can be separated and collected then TLC

20
Q

Draw a Diagram for GC

A
21
Q

What is the Stationary Phase for GC? (3)

A

-Silica Or Alumina powder coated with oil

-Packed into a long thin Capillary Tube

-Coiled and placed into a warming oven

22
Q

What is the Mobile Phase for GC?

A

Inert Carrier Gas - such as N2, Ar or He

23
Q

What are the advantages of GC?

A

Very Sensitive instrument - can detect traces of substances

(can link oil pollution to specific ships, and detect certain types of chemicals in foods)

24
Q

What are some of the common uses of GC?

A

Blood/Urine alcohol & drug testing - breathalyser test

25
Q

How can you use GC or GCMS to identify Substances? (3)

A
  • Separate mixture using GC, and record retention time
  • test each component with an MS spectrometer

-Use combination of the Fragmentation pattern/ molecular ion peak graph from the MS with the retention time from GC.

  • To compare with accepted values of known substances .
26
Q

How does GCMS work?

A

GC is run, separating the mixture and recoding each of the components retention time

Separated components are then run through an MS spectrometer.

Fragmentation pattern/ molecular ion peak confirms the identity of the substance

27
Q

Which organic substance will have a shorter retention time?

Aldehyde or Alcohol (4)

A

Aldehyde

-Has a Less of a polar bond then an alcohol (more soluble)

  • it adsorbs less strongly to the stationary phase.
  • so moves through the column/plate at a faster rate due to less attractive forces with the stationary phase
28
Q
A

Plastic gloves prevents contamination of TLC plate

Adding developing agent at a depth below 1cm^3 - if the solvent is too deep it will dissolve the mixture from the plate

Solvent doesn’t need to rise to the top as an Rf value can be calculated regardless

Fume cupboard is used as the solvent is toxic

29
Q
A

Amino acids have different bonds and polarities

Therefore have a difference balance between the affinities for the mobile and stationary phases

Resulting in different retention Times

Chemistry (A2) (15 decks)

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