Experiment You have to separate a solid mixture of two compounds (benzophenone and biphenyl) using column chromatography. You perform a preliminary TLC and you determine that a mixture of ethyl acetate: hexane = 50:50 is the best solvent.
1. Which one of the two compounds you expect to be eluted first? Explain your answer.
2. You prepare the column, put the sample at the top of the column and pass through a mixture of ethyl acetate: hexanes = 50:50 and collect fractions as they are dripping at the bottom of the column. Analysis of the collected portion through TLC shows that the compounds did not get separated and the solvent mixture suggested by the preliminary TLC did not work as expected. Propose a possible cause.
3. In an effort to attempt to correct the outcome from question 2 you will use only hexanes as the solvent. Analysis of the collected fraction shows the presence of only one compound. Which one do you think it is, benzophenone or biphenyl? Where is the other compound? Explain your answer.
4. In an effort to attempt to correct the outcome from question 2 you will use only ethyl acetate as the solvent. Analysis of the collected fraction shows the presence of only one compound. What outcome do you predict? Which one do you think it is, benzophenone or biphenyl? Explain your answer.
5. What would be in your opinion the best way to use the two solvents to ensure a good separation? Explain your answer. Be specific about order of addition to the column, concentration, etc.