Equilibrium II & electrochem  test        [90 points]                            AP chemistry

 

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.

 

                                                                                                Signature:  ___________________

 

 

1.  Qualitatively, describe 2 methods to prepare a lactate buffer, where the pH = 4.0; while need not do any calculations, include any relevant equation(s).  [10 points]

 

 

2.  In regards to the electrolysis of water, sketch the electrochemical cell, include  __.   [15 points]

(i)  the direction of current in the system & justify your answer

(ii)  half-reactions at each electrode & identify the cathode & anode

(iii)  is it an electrolytic or voltaic cell ?  define these terms & justify your answer.

 

 

3.  What is the pH after the addition of __.  [20 points]

 

a.  15.0 mL of 50.0 mM potassium hydroxide to 60.0 mL of  25.0 mM nitric acid. 

 

 

b.  15.0 mL of 50.0 mM hydrochloric acid to 40.0 mL of  25.0 mM sodium hydroxide.

 

 

 

4.  What is the pH after the addition of  ___.  [20 points]

 

a.  15.0 mL of 50.0 mM potassium hydroxide to 60.0 mL of  25.0 mM hydrofluoric acid.

 

b.  a.  15.0 mL of 50.0 mM potassium hydroxide to 60.0 mL of  a mixture containing 25.0 mM acetic acid and 20.0 mM sodium acetate.

 

 

 

5.  For each of the following reactions, in part (i) write a BALANCED equation and in part (ii) answer the question about the reaction.  Coefficients should be in terms of lowest whole numbers.  Assume that solutions are aqueous unless otherwise indicated.  Represent substances in solutions as ions if the substances are extensively ionized.    [15 points]

 

a.  calcium added to a solution of hydrochloric acid

 

i.

 

ii.  20.0 g calcium + excess hydrochloric acid produces the equivalent of  __ L of gas @ STP

 

b.   mix solutions of copper (I) chloride and tin (II) chloride

 

            i.

 

            ii.  justify that the reaction is spontaneous

 

c.  the combustion of ethane

 

            i.

 

            ii.  identify the reducing agent

 

6.  How much time would be needed to plate 100.0 mg zinc onto a carbon electrode, where the current = 2.0 A ?   [10 points]