Chemistry 241 Midterm Name ___________________________________

 

Summer 1998 100 pts

Lab TA _____________________________

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    1. (16 pts) A graph of the solubility of Compound A in water is given above. Use this graph to answer the following questions.

    (a) Suppose you have 500 mg of Compound A. What is the minimum volume of boiling water needed to completely dissolve the sample?

     

     

     

     

    (b) A student dissolves 1000 mg of Compound A in 4 mL of boiling water and slowly cools the solution. At what temperature would one expect crystals to begin to appear?

     

     

     

     

    (c) The student in part (b) collects crystals at 20 ūC. What is the maximum mass of Compound A that can be recovered at this temperature?

     

     

     

     

    (d) Approximately how much more of Compound A would be recovered from part (b) if, instead, the student had cooled the solution to 0 ūC?

     

    2. (18 pts) On the liquid-solid phase diagram for a two component mixture (compounds A and B) given below, label each of the following:

    The structures and melting points of 2-methylbenzoic acid, benzoin, 4,4’-dihydroxybenzophenone and 4-aminobenzophenone are shown below. Use this information to answer questions 3-5.

     

    3. (8 pts) Draw the structure of the compound that is present in the aqueous layer when an ether solution of the above compounds is extracted with an aqueous solution of NaHCO3 (sodium bicarbonate)

     

     

     

     

     

     

    4. (14 pts) You are given a sample that consists of sand, 4-aminobenzophenone and benzoin. The two organic compounds are soluble in boiling water but insoluble in cold water. The two organic compounds are completely soluble in ether. Sand is completely insoluble in both water and ether. Briefly describe how you would separate and isolate each of the three components using techniques that you have learned in Chemistry 241 lab.

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

    5. (8 pts) A sample that is purported to be crude 4-aminobenzophenone has a melting point of 128-131 ūC. Indicate whether this sample is likely to be 4-aminobenzophenone and explain the reasoning for your answer.

     

     

     

     

     

     

    6. (12 pts) Arrange the following molecules in order of increasing polarity (least polar first):

     

     

    ________ > ________ > ________ > ________

    least polar most polar

    7. (8 pts) The reaction of bromine with cis-cinnamic acid gives only the threo isomer of 2,3-dibromo-3-phenylpropanoic acid. Draw the chemical structure of an intermediate that explains the stereochemical outcome for this reaction.

     

     

     

     

     

     

     

     

     

    8. (16 pts) The distribution coefficient for solute A between water and diethyl ether is 1.0. Suppose that 100 mg of solute A is initially dissolved in 1.0 mL of water.

    (a) Calculate the mass of solute A extracted by 0.5 mL of ether.

     

     

     

     

     

    (b) Calculate the mass of solute A extracted when the water phase remaining in part (a) is extracted a second time with 0.5 mL of ether.

     

     

     

     

     

    (c) Calculate the amount of solute A extracted by a single extraction with 1.0 mL of diethyl ether.

     

     

     

     

     

     

    (d) How much more of solute A is extracted by the two 0.5 mL extractions compared to the single 1.0 mL extraction?