Question

For the lab practical experiment, you will be given a 1.00-8 sample of benzophenone contaminated with benzoic acid. Your task is to write your own protocol and complete as much of it as possible in a 2-hour period, with the objective being to obtain a pure sample of benzophenone in the highest percent recovery. Techniques to consider when writing your protocol include the following: • Recrystallization • Extraction • Column chromatography • TLC/mp/bp • Distillation Reflux Drying of organic solvents Evaporation Vacuum and gravity filtration

I need step by step and all details of this experiment as a protocal.

Answer 1

Notice that both the benzophenone and benzoic acid are the solids. For purifying solid compounds, recrystallization is the best technique.

Hence, Recrystallization is the best technique to obtain a pure sample of benzophenone in the highest percent recovery.

During the recrystallization process, you have to select a solvent in which only benzoic acid is soluble, but not benzophenone. Then you can get rid of all the benzoic acid contaminated in the benzophenone. Then if you want still purer benzophenone, you can dissolve benzophenone in a minimum suitable solvent, and add few drops of non-solvent, where the compound (here, benzophenone) is partially soluble/insoluble. Then pure compound of benzophenone will be crystallized out from the solution, you can simply filter all the crystals of benzophenone and dry under vacuum to get rid of solvent traces.

Note: Using TLC, benzophenone will have a higher Retention factor (R_f) than the benzoic acid. As a result, you can separate them using column chromatography in which you have to select a suitable solvent mixture (Hexane + ethyl acetate) in which benzophenone having higher R^f value will be eluted first from the column.

But, column chromatography is not an accurate method for purifying solid compounds, if you wish you can perform column chromatography also, but it will take more time.