Choosing the Best Recrystallization Solvent PDF

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Summary

this lab is based on the method of recrystallization and involves an experiment to decipher which solvent is best to recrystallize specific solids....

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1

Lauren Franklin

03/20/2021

Title: Lab #12 Recrystallization Objective: The purpose of this experiment is to utilize the process of recrystallization to determine the best recrystallization solvent or solvent pair- water, methanol, ethanol, acetone, acetic acid, toluene, or ligroin- for solids resorcinol, anthracene, and benzoic acid. Questions: Online class do not need to write lab report for this lab. Please answer the two questions: 1) indicate which solvent recrystallizes which solid, and what is the shape of the crystal. -

For recrystallization, an ideal solvent is one in which the compound is insoluble at room temperature, but dissolves at the boiling point. Using solvent toluene only, Resorcinol recrystallizes in the shape of white, small rock-shaped crystals. Ligroin is an ideal recrystallization solvent for Benzoic Acid and forms clear, little snowflakelike crystals. For Anthracene, the ideal solvent is 95% ethanol and recrystallizes, leaving behind clear-white circular crystals.

2) What suggestions you would give to obtain better crystals, based on the videos in page 1 of this lab manual? -

I suggest utilizing methods in the Recrystallization video to ensure and/or test for purity of the compounds. Such methods include the Decoloration test which uses charcoal, boiling and an optional filtration agent as well as hot filtration. If you choose to perform hot filtration, you must boil away the excess solvent until the solid forms and then cool for crystallization. This can be a tedious process, but the low crystal growth (rather than quick method used by the student) is more advantageous when in a cold laboratory. Furthermore, you can watch closely just as the crystals form, giving the student a more interactive and valuable learning experience. After crystals form, I suggest using vacuum filtration which enables the student to collect the dry, newly formed crystals and reserve the mother liquor for future crystallizing....