The solubility of benzoic acid in water is 6.80 g per 100 ml. at 100 degree C an
ID: 533845 • Letter: T
Question
The solubility of benzoic acid in water is 6.80 g per 100 ml. at 100 degree C and 0.34 g per 100 mL at 25 degree C. (a) Calculate the minimum volume of water needed to dissolve 1.00 g of benzoic acid at 100 degree C. (b) Calculate the maximum theoretical percent recovery from the recrystallization of 1.00 g of benzoic acid from 15 mL of water, assuming the solution is filtered at 25 degree C. The solubility of acetanilide in your recrystallizing solvent is 5.0 mg per mL at 10 degree C. (a) Calculate the maximum percent recovery in this experiment, assuming a 15.0-mL recrystallizing solution is filtered at 10 degree C. (b) Calculate the percent recovery of the acetanilide produced in your experiment. (c) How do your results compare to the maximum percent recovery? Briefly explain. A student rushed through this experiment. Describe the effect that the following procedural changes would have on the percent recovery of acetanilide. Briefly explain the basis of each answer. (a) Rather than adding 0.5-mL portions of boiling solvent to the acetanilide, the student added 5-mL portions of boiling solvent. (b) The student did not pre-heat the gravity filtration apparatus in Part 3. (c) The student forgot to cool 5 mL of solvent in Part 5 and washed the crystals with room-temperature solvent.Explanation / Answer
1. Benzoic acid
(a) Volume of water needed = 1.0 g x 100 ml/6.8 g = 14.7 ml
(b) benzoic acid in solution at 25 oC = 0.34 g x 15 ml/100 ml = 0.051 g
%Recovery at 25 oC starting with 1.0 benzoic acid at 25 oC = (1 - 0.051) x 100/1.0 = 94.9 %
3. Errors in experiment,
(a) If 5 ml solvent is added, excess solvent would keep all of acetanilide in solution and nothing will precipitate out when cooled at 10 oC.
(b) Crystals of acetanilide would form on the filtration apparatus as the solution would cool down immediately when comes in contact with apparatus.
(c) The crystals would dissolve when washed, so lower yield of compound is expected.