please help with question 1 and 2. section name Post-Laboratory Questions 1. The
ID: 1077033 • Letter: P
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please help with question 1 and 2.
section name Post-Laboratory Questions 1. The solubility of benzoic acid in water is 6.80 g per 100 mL at 100 C and 0.34 g per 100 mL at 25 °C. (a) Calculate the minimum volume of water needed to dissolve 1.00 g of benzoic acid at 100 C (b) Calculate the maximum theoretical percent recovery from the recrystallization of 1.00 g of ben- zoic acid from 15 mL of water, assuming the solution is filtered at 25 °C. 2. The solubility of acetanilide in your recrystallizing solvent is 5.0 mg per ml at 10 °C. (a) Calculate the maximum percent recovery in this experiment, assuming a 15.0-mL recrystallizing solution is filtered at 10 °C. (b) Calculate the percent recovery of the acetanilide produced in your experiment. (c) How do your resu Its compare to the maximum percent recovery? Briefly explain. 3. 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. Given data:
The solubility of benzoic acid in water at 100 oC = 6.8 g/100 mL
The solubility of benzoic acid in water at 25 oC = 0.34 g/100 mL
a. The minimum volume of water needed to dissolve 1.00 g of benzoic acid at 100 oC = 100/6.8 = 14.706 mL
b. Note: During the recrystallization of benzoic acid in water, you first need to dissolve 1 g of it at 100 oC, then you need to cool it to room temperature, i.e. 25 oC, followed by filtration. That's why you need to subtract the solubilities at 100 oC and at 25 oC to get the amount that precipitates after cooling the solution from 100 oC to 25 oC.
The difference in the solubility of water at 100 oC and at 25 oC = (6.8-0.34) g/100 mL = 6.46 g/100 mL
Now, per 15 mL, the solubility difference = (15/100)*6.46 = 0.969 g, i.e. 0.969 g/15 mL
Therefore, the maximum theoretical percent recovery from the recrystallization of 1.00 g of benzoic acid from 15 mL of water, where the solution is filtered at 25 oC = (0.969 g/1.00 g)*100 = 96.9%
The remaining, i.e. 1 - 0.969 = 0.031 g of benzoic acid will be in the filtrate.
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