Specific Information for the Partition Coefficient Experiment

Your report will consist of the following sections. Use the headers listed below to designate each section, except for the Title.

Title: The title of the experiment, the experiment number, and the date that the experiment was performed in lab. This information is identical to that required in your pre-lab write-up. The title should be complete and accurate:

Experiment 4A: Determination of a Partition Coefficient for Benzoic Acid in Methylene Chloride and Water, and Experiment 4B: Solvent Extraction I: Acid-Base Extraction Using the System Benzoic Acid, Methylene Chloride, and Sodium Bicarbonate Solution.

An incomplete title such as "Experiment 4A: Determination of a Partition Coefficient" is not sufficient.

Objective: List the goals, or the purpose, of the experiment. This information is identical to that required in your pre-lab write-up.

Experimental Procedure: You do NOT need to copy the experimental details that were included in your pre-lab write-up.It is sufficient to include a reference to the source of the procedure, as well as any modifications that were posted on Blackboard. If necessary, these statements should be followed by a list of any additional modifications to the experimental procedure. It is very important that you document any changes to the procedure in your lab notebook at the time of the experiment, and include them in your report. This section may help to explain unexpected results, for instance.

Experiments 4Aand 4B were followed as described in Mayo, pages 144-147, with themodificationslisted in the Blackboard document.

Reaction Scheme: A balanced chemical reaction consistent with the experiment being conducted, including reactants, products, solvent(s), and reaction temperature. This scheme is identical to that required in your pre-lab write-up and should immediately precede the Data and Results Table (see below). The reaction scheme may be hand-written, but please be as neat and clear as possible.

For 4A, there is no chemical reaction involved in the partition coefficient experiment. In this case, simply draw the chemical structure of the compound that is being partitioned - benzoic acid.

For 4B, include a complete and balanced chemical equation for the reaction that occurs in this extraction procedure.

Using any form of electronic copy and paste to reproduce directly a reaction scheme from any source, including the printed or electronic lab textbook, is a violation of the Academic Integrity policies of this course.All parts of your lab report - text, schemes, tables, etc. - must be in your own words. You may draw the reaction scheme by hand (preferred), or use some type of drawing program, but it must be your own work.

Data and Results: Organized in three parts as shown below.

Data and Results Table

Give original data and calculated values in an organized tabular format, essentially, an updated version of the Reaction Table from your pre-lab.

• Include appropriate units and pay attention to significant figures.
• Data may differ slightly from that reported in your pre-lab write-up. For example, you may have weighed 77 mg of benzoic acid rather than the prescribed 75 mg. That is no problem at all, but you must report and use the actual values in your calculations. In this way, your final results and conclusions match what you actually did in the experiment, not what you intended to do in your pre-lab.

You may use the following table as a template. In the future, you will be responsible for creating your own table (either written by hand, or using Word or Excel). This template is to help set expectations. In the future, as with the Reaction Scheme, using any form of electronic copy and paste to reproduce directly a data table from any source, including the printed or electronic lab textbook, is a violation of the Academic Integrity policies of this course.

Sample dataare included for Experiment 4A. Complete the table with your experimental data and calculations.

*Initial amount only is needed in the table. The amount used to rinse may vary and is not relevant

to the partition coefficient calculation

Observations

Data includes all relevant observations, such as heat evolved, initial color and color changes, precipitate formation, etc. Observations should be listed in bulleted, complete sentences.

Calculations

For all calculated values in Chem 2203, show ALL work. This part does not have to be typed, and you may prefer to leave space in your document and enter the calculations by hand. Please be as neat as possible.

Show ALL work! Write or type all three calculations for each experiment (6 total) and include all units:

1)  Benzoic acid in CH₂Cl₂ = (final weight of vial + boiling stone + solid) - (weight ofvial + boiling stone)

2)  Benzoic acid remaining in aqueous layer (either water for 4A or 10% sodium bicarbonate solution for 4B

3)  Benzoic acid K_pCH₂Cl₂/H₂Ofor 4A andK_pCH₂Cl₂/aq. NaHCO₃for 4B

Note that for Experiment 4B, this calculation does not provide a true partition coefficient because benzoic acid is chemically modified in the procedure. The value is still useful for illustrating the distribution of benzoic acid and its derivatives between the two phases.

Questions: Answer the following questions. Be as complete as possible, and always explain your reasoning.

1. Laboratory glassware comparison for solvent extraction: concial vial vs separatory funnel...

a)  Which piece of laboratory glassware did you find to be more efficient for the solvent extraction procedure, and why?

b)  Assuming ideal separatory funnel performance (complete phase separation and no loss of solvent into the stem during venting), which piece of laboratory glassware provides a more accurate determination of the partition coefficient, and why?

2. Draw the chemical structure of benzoic acid and use it to answer the following solubility-based questions:

a)  Circle and label the region of the molecule that exhibits non-polar behavior.

b)  These non-polar regions interact with solvent molecules with what types of intermolecular forces (list all that apply): hydrogen bonding, dipole-dipole, dipole-induced dipole, or induced dipole-induced dipole (London dispersion)?

c)  Circle and label the region of the molecule that exhibits polar behavior.

d)  This polar region interact with solvent molecules with what types of intermolecular forces (list all that apply): hydrogen bonding, dipole-dipole, dipole-induced dipole, or induced dipole-induced dipole (London dispersion)?

e)  Based on the answers to parts (a)-(d) and Question 1 from the Partition Coefficient Part A lab report, predict whether benzoic acid will be more or less soluble in water than 9-fluorenone. Explain your answer.

3. In Experiment 4B, a chemical reaction occurred to form sodium benzoate. This chemical reaction should be included in the Reaction Scheme section (hint: review common types of chemical reactions in aqueous solutions from general chemistry).

a)  Sodium benzoate is formed from benzoic acid by what common type of chemical reaction that occurs in aqueous solutions?

b)  What is the role of sodium bicarbonate in this reaction?

c)  Draw the chemical structure of sodium benzoate and include all charges

d)  Circle and label the region of the molecule that exhibits polar behavior

e)  What is the strongest intermolecular force with which sodium benzoate will interact with the solvent water?

4. Consider the calculated partition coefficents for Experiments 4A and 4B.

a)  Was there a significant difference in the two K_p values? If so, which one was larger?

b)  Provide an explanation for your answer in part (a). Be as complete and specific as possible. Hint: see Question 3.

Works Cited: Full references for the experimental procedure(s) in the following format:

1. Mayo, D. W.; Pike, R. M.; Forbes, D. C. Microscale Organic Laboratory with Multistep and Multiscale Syntheses, 5^th ed.; John Wiley & Sons, Inc., 2011; pp 141-147.

2. Modifications for Expts 4A and 4B: Partition Coefficient Part B and Solvent Extraction I, Blackboard document.