 # Purifying Acetanilide By Recrystallization Process

Purifying Acetanilide By Recrystallization Process
Purifying 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?
13
Solvent Extraction, Pre-lab page 2
(e) How would the results differ if you added sodium p-toluate instead of p-toluic acid to the
two-layer mixture of diethyl ether and water?
4. How many milliliters of 3.0 M HCl would be required to neutralize 30. mL of 0.50 M
NaOH? (Show your work). (hint: this is a general chemistry question! Remember that the
acid HCl and the base NaOH react in a 1:1 molar ratio. The number of moles of acid need to
equal the number of moles of base to effect complete neutralization).
5. Briefly explain how you will isolate p-toluic acid after it is extracted it into NaOH solution.
6. Write the equation for the chemical reaction of the toluate ion that will occur when you
add HCl solution to the NaOH extract in part 3.
SN1 Reaction: A Kinetic study
Post-Laboratory Questions (attach your responses on a separate sheet)
1. From the experimental data, prepare a table of the following values. Record all calculated
results to the proper number of significant figures. Note that V and V¥ are the total volumes of
NaOH solution delivered; they are not burette readings (unless, of course, your initial buret
reading was 0.00 mL). Base your calculations on the actual value of V¥ that you measured in lab
– not the theoretical value! Time, t, is the elapsed time in seconds (its OK to use minutes if you
prefer). Use Equation 10 to calculate the values of k.
t (sec) V (mL) V/V¥ (1 – V/V¥) ln(1 – V/V¥) k
2. Prepare a graph of ln(1 – V/V¥) versus time, t. Using a computer program or a graphing
calculator, determine the best straight line through your data points. (See the supplement to this
lab for detailed instructions on how to determine best fit if you are unfamiliar with this process).
This graph should be properly labeled and drawn to scale. Do the data support the SN1
mechanism? Briefly explain.
3. Calculate the value of k from the slope of the line from the graph in 2.
4. Using the values of k which you determined above (in question

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