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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? you may have observed. Why is the theoretical maximum percent recovery (calculated in 2a above) not necessarily applicable your experiment? (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, 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 , or ? 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. 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. . 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 (C H —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: solubility in water: solubility in ether: solubility in ether: 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). 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 -toluic acid be more soluble if -toluic acid were added to a two-layer mixture of diethyl ether and water? Solvent Extraction, Pre-lab page 2 (e) How would the results differ if you added sodium -toluate instead of -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? ( ). (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 -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. (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 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 – ! Time, t, is the elapsed time in seconds (its OK to use minutes if you prefer). Use Equation 10 to calculate the values of . 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). . Do the data support the S 1 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 #1), calculate the average value of and estimate its uncertainty. One way to estimate its uncertainty is to (1) calculate an average value of (2) calculate the absolute value of the deviation of each value from the average value (3) calculate the average of these deviations. Prepare a table which shows the deviation for each datum, and report the average value of and the average deviation. It may be convenient for you to include these data in the table you prepare for post-lab question #1, above. Note: What you are doing here is a standard statistical way of measuring . Theoretically, the value of k should be the same for all trials. In practice, however, you almost certainly will observe some variation in the calculated values of k. The average deviation is a way of expressing in a single number how much variability you have in your data. Low average deviations mean your numbers are all close together; high average deviation means you have a lot of “noise” or “scatter” in your data. S 1 Reaction: A Kinetic Study Name ________________________________________________________________ . 1. Describe briefly the hazards associated with the reaction mixture and the safety precautions you must take when performing the experiment. 2. Assume that you use 1.00 mL of 2-chloro-2-methylpropane. Calculate the following quantities. a. the number of moles of 2-chloro-2-methylpropane used. The density of the liquid is 0.851 g/mL.