Chromatography

Question 1

What is the principle of chromatography?

Answer 1

• a mixture can be separated if it is dissolved in a solvent and then the resulting solution ( now called the mobile phase) moves over a solid (the stationary phase)

Question 2

What is the mobile and stationary phase? What happens in these stages?

Answer 2

• mobile phase
  
  • carries the soluble components of the mixture with it
  • the more soluble the component, the fast it moves
• stationary phase
  
  • hold back the components in the mixture that are attracted to it
  • the more affinity of a component in the mixture being serparated to the stationary phase, the slower it movess in the solvent

Question 3

What is the eluent?

Answer 3

• the solvent in the moving phase is often called the eluent
• in column chromatography

Question 4

How is TLC plate different from the filter paper in paper chromatography?

Answer 4

• filter paper replaced by a glass, metal, or plastic sheet, coated with a thin layer of silica gel (silicon dioxide) or alumina (aluminium oxide) which acts as the stationary phase

Question 5

WHat are the advtages of TLC of paper chromatography?

Answer 5

• runs faster
• smaller amounts of mixture can be separated
• spots usually spread out less
• plates are more robust than paper

Question 6

What happens when the spots are colourless?

Answer 6

• may be located by shining UV light on the palte
• or spraying plate with a locating agent which reacts with the components of the mxiture to give coloured compounds

Question 7

WHat is the Rf value?

Answer 7

distance moved by spot / distance moved by solvent

Question 8

What determines the distance travelled

Answer 8

balance between solubility in moving phase and retention by stationary phase