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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 in band A are most strongly adsorbed to the stationary phase. This is because they have moved the least distance down the column, indicating a stronger interaction with the alumina.
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 increase the frequency of adding water during the chromatography process. This would help to further develop the separation of components in band B by allowing them more time to migrate through 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
Band A would contain the component with the smallest Rf value because it is the most strongly adsorbed to the stationary phase. In chromatography, a smaller Rf value indicates a greater interaction with the stationary phase and less movement through the mobile phase.
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
Band C contains the component that would have the smallest retention time. This is because components in band C are less polar and interact less with the alumina stationary phase, allowing them to elute faster in a high-performance liquid chromatography setup.