Photo AI
A burette packed with finely divided alumina powder (Al2O3) was used to separate the components in a plant extract by chromatography - VCE - SSCE Chemistry - Question 2 - 2006 - Paper 1
Question 2
A burette packed with finely divided alumina powder (Al2O3) was used to separate the components in a plant extract by chromatography. The alumina acts as the station... show full transcript
Worked Solution & Example Answer:A burette packed with finely divided alumina powder (Al2O3) was used to separate the components in a plant extract by chromatography - VCE - SSCE Chemistry - Question 2 - 2006 - Paper 1
Step 1
In which one of the three bands, A, B or C, were the components most strongly adsorbed to the stationary phase?
Answer
The components that are most strongly adsorbed to the stationary phase typically move the least during chromatography. This means that the components in band A are the ones that are most likely to have been retained in the alumina because they have not moved up the column as much as bands B and C.
Step 2
Band B starts to show signs of separating into two different bands just before it emerges from the bottom of the burette. Give one possible modification that could be made to this experiment to more effectively separate band B into its separate components.
Answer
One possible modification is to reduce the flow rate of the mobile phase. Slowing down the elution could provide more time for the components in band B to separate as they interact with the stationary phase.
Step 3
In another experiment, the components in the plant extract were separated in a similar way to paper chromatography, using a glass sheet coated with alumina and water as the mobile phase. Which one of the three bands, A, B or C, contains the component that would be most likely to have the smallest Rf value? Explain your answer.
Answer
The component in band A would have the smallest Rf value because it is the most strongly adsorbed to the stationary phase (alumina) and would thus travel the least distance on the chromatogram.
Step 4
Which one of the three bands, A, B or C, contains the component that would have the smallest retention time if this separation was conducted using a high-performance liquid chromatograph with alumina as the stationary phase? Explain your answer.
Answer
The component in band C is expected to have the smallest retention time as it is less strongly adsorbed to the stationary phase, allowing it to pass through the chromatograph more quickly than the components in bands A or B.