CHEMISTRY

urifying Acetanilide by

Recrystallization

 

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.

Show your calculations for the questions below.

(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 benzoic

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. (10ºC is the

approximate temperature of an ice/water bath). Show your calculations for the questions below.

(a) Calculate the theoretical 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 results compare to the theoretical maximum percent recovery? Explain any difference

you may have observed. Why is the theoretical maximum percent recovery (calculated in 2a above) not

necessarily applicable your experiment? Aside from technical or human error (such as spillage,

incomplete transfers, loss on the filter paper, loss due to excessive washing, etc.) or slight differences involume of solvent or temperature of the ice bath, what assumptions or estimations were made in this

calculation which may not apply to your results?

3. A student rushed through this experiment. Describe the effect that the following procedural changes

would have on the percent recovery of acetanilide; would the % recovery by higher, or lower? 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 forgot to cool 5 mL of solvent in Part 4 and washed the crystals with room-temperature

solvent.

 

 

 

 

 

Separating Acids and Neutral Compounds by

Solvent Extraction

1. Based on the amounts of p-toluic acid and acetanilide you recovered, estimate the

composition of the original mixture, assuming that you lost equal amounts of each

compound. Show your calculations. Express the composition as percentages of each

component: For example “the original mixture was 30% p-toluic acid and 70%

acetanilide”.

2. What product would you obtain if you evaporated the water from the NaOH layer prior to

acidifying the layer?

3. Suppose that you used dichloromethane instead of diethyl ether as the nonpolar solvent in

this experiment. What changes in the procedure would you make in view of the fact that

dichloromethane is more dense than water?

 

4. Benzoic acid (C6H5—COOH) is a weak acid and naphthalene is neutral, neither acidic or

basic. Prepare a flowchart for the separation and recovery of benzoic acid and

naphthalene.

Benzoic Acid Naphthalene

solubility in water: poor solubility in water: poor

solubility in ether: good solubility in ether: good

5. After comparing the melting points of each of your compounds to their respective

literature values, comment on the purity of each compound. (You may skip this question if your

instructor did not have you acquire melting points).

O OH

 

 

 

1. Briefly describe the hazards you should be aware of when you work with:

(a) diethyl ether

(b) 3M HCl

2. Briefly explain or describe the following:

(a) How would you determine which layer is the aqueous layer after you add NaOH solution to

the ether solution of your compounds?

(c) What visible evidence(s) of reaction will you see when you acidify the NaOH extract with

HCl solution?

(d) In which layer would p-toluic acid be more soluble if p-toluic acid were added to a two-layer

mixture of diethyl ether and water?

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