Ch. 20   electrochem     test                 [110 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.  Clearly identify the problems done and do them in sequence and your answer must begin and end on the same page of paper; otherwise, you will lose points.  attach this sheet to the front of your exam.


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.  Write the balanced net ionic equation describing the reaction of mixing an acidic aqueous solutions of potassium dichromate and sodium iodide.  [15 points]



2.  Sketch the electrochemical cell for the reaction:  Zn  +  Cu(NO3)2  à Cu  +  Zn(NO3)2 using a zinc and carbon electrode;  (i) label the electrodes, (ii) show the direction of current, (iii) write the half-reaction at each electrode, and (iv) label the cathode and anode.   [20 points]



3.  In an electroplating experiment to coat an electrode with zinc, you have 15.0 minutes to coat 100.0 mg Zn onto the electrode.  What is the current ?  [10 points]


 4.  In the redox reaction: ; what is the cell potential @ 25 °C ?  [15 points; sample problem 20.11]


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.    [30 points]


a.  calcium added to a solution of hydrochloric acid




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



            ii.  justify that the reaction is spontaneous


c.  the combustion of ethane




            ii.  identify the reducing agent



6.  In regards to the reaction:   determine ___.  [10 points]

a.  cell potential at 35 ° C

b.  equilibrium constant at 25 ° C


7.  old topic:  what is the trend in acid strength in a __ in the periodic table;  what is the rationale of this trend ?  [10 points] 


a.  row



b.  column