To a reflux apparatus add 90 mL of ethanol and 35 g of benzil, heat the solution to almost boiling with stirring. Dissolve 35 g of potassium hydroxide in 70 mL of cold water. Add the hydroxide solution dropwise to the reflux apparatus. Then reflux for 15 minutes, pour the solution into a beaker and cover it up with wrap put it into a freezer for 5 h to crystallize the sodium salt. Filter. Dissolve the crude salt in 350 mL of water, heat to dissolve all of the product, then start adding conc. HCl until the pH is very acidic. Cool down in freezer, filter and wash with cold water. Recrystallize with hot ethanol.
Benzil dissolved in the solution when heated
After addition of the potassium hydroxide, the solution turned black
Cooling the solution down in a freezer
After cooling down in the freezer the potassium salt crystallized, the solution was filtered
HCl was added and the mixture was cooled down in the freezer
Filtration of the benzilic acid