test:  Ch. 20 & 25  electrochem, organic- / bio- chem             95 points                                              AP chem

 

For problems involving calculations, show your work in an organized manner, include any relevant equation (or formula and conversion factor(s)), put the proper units in your calculations / answer, and have the proper number of significant figures in your answer. 

Academic Honesty:   The answers on this test are my own and I am using only the allowed set of notes as described in the syllabus.  I have not discussed the test questions with anyone before or during the test nor have I seen the test questions prior to the exam.  If you violate any of the preceding items or do not sign, your semester grade is a F.

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1. Under standard conditions, an electrochemical cell has a tin electrode in an aqueous solution of tin (II) chloride and a zinc electrode in an aqueous solution of zinc chloride.  [20 points]

a. What is the (spontaneous) redox reaction in this electrochemical cell ?  Justify your answer.

b. Sketch this voltaic cell; label:  electrode (i.e. zinc vs. tin), cathode vs. anode; half-reaction at each electrode, direction of current, and direction of the movement of ions in the salt bridge.

c. Rather than standard conditions, the [tin II ion] = 100. mM, [zinc ion] = 10.0 mM, and the temperature is 25 ºC.  A voltmeter is connected to the system; what is the expected voltage ?  FYI; volt = Joule per coulomb.

2. How much time (in hours) is needed to generated 224 mL of oxygen gas at 25 ºC and 1.0 atm in the electrolysis of water using a current of 250.0 mA ?  [15 points]

3. How would an increase in temperature change the cell voltage (i.e. increase, decrease, no change, or ambiguous) in an electrochemical cell / redox reaction under standard conditions ?  Justify / rationalize your answer.   [15 points; hint: prior test question]

4. Draw three structural formulas of isomers of heptane.  [10 points]

5.  Draw the structural formula of __ with a methyl group.  [15 points]

a.  ketone

b. Amine

c. Carboxylic acid

 

6. Old topic:  Based on the below reaction energy profile, ___.  [20 points]

http://s3.amazonaws.com/answer-board-image/3fdc5664-f7bc-4141-be14-d2fbc0fa3d75.png

a. using the Roman number to represent various chemicals, write the reaction mechanism

b. In the above diagram, (i) clearly label the ΔH (ΔH1, ΔH2, etc.) for each step in the reaction mechanism and (ii) is it’s value:  positive, negative, zero, ambiguous   (put your answer on the right of the above diagram)?

c. What is the slowest step in the mechanism ?  Justify your answer.

d. using the Roman number to represent various chemicals, identify the reactant(s), product(s), intermediate(s) and catalyst(s) in the reaction.