Question

1. Retention time (tR) is a measure of how long a compound is retained on a stationaryphase in column in column chromatography. In TLC, Rf was a measure of how long thecompound was retained on the stationary phase. What is the relationship between tR and Rf?

2. What would be the order of elution if one separated the pigments of spinach on columnchromatography?

3. What if any would you have to change in terms of the mobile phase if you wanted toactually perform the column chromatography in order to separate the pigments of spinachcompare to the one used for the TLC Experiment? Explain.

4. Why is it important to keep the solvent level above the stationary phase? What wouldhappen if one lets the solvent get much lower than the alumina stationary phase?

Answer 1

1. Retention time (tR) is a measure of how long a compound is retained on a stationaryphase in column in column chromatography. In TLC, Rf was a measure of how long thecompound was retained on the stationary phase. What is the relationship between tR and Rf?

Solution :- tR is the time that the component of the mixture reatin in the stationary phase and Rf is the ratio of the distance traveled by the solute to the distance traveled by the solvent in the TLC

Both these values gives the idea about the polarity of the compoenents of the mixture and the solvent system needed for the effective separation of the components.

2. What would be the order of elution if one separated the pigments of spinach on columnchromatography?

Solution :- The spinach contains different chemicals with varialbe polarity the chlorophyll is the most polar than the carotene pigment therefore increasing the polarity of the solvent system we can separate the chlorophyll first and then separate the carotene.

3. What if any would you have to change in terms of the mobile phase if you wanted toactually perform the column chromatography in order to separate the pigments of spinachcompare to the one used for the TLC Experiment? Explain.

Solution :- Changing the mobile phase will alter the separation of the components. If the non polar solvent system is used then non polar components will separate first and if the polarity of the solvent system is increases then polar components will separate first. Therefore changing the mobile phase can change the separation of the components.

4. Why is it important to keep the solvent level above the stationary phase? What wouldhappen if one lets the solvent get much lower than the alumina stationary phase?

Solution : - Solvent must be reached to the all the parts of the components so that they can mix with the mobile phase and get separate easily. Therefore it is important that solvent must be above the level of the stationary phase so that all the components get mixed with the solvent. If the solvent is not above the stationary phase then solvent would not reach to all the parts of the mixture so they cannot separate well.