Ch. 17, 8.10, & 20  equilibrium & electrochem                       test       80 points                      ap chemistry

Show your work in an organized manner, include (i) any relevant equation (or formula), (ii) conversion factor(s), (iii) put the proper units in your calculations and answer, and (iv) 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. In the below (hypothetical ?) redox reactions, identify the species that (i) oxidized and its oxidation number next to it above the chemical equation and (ii) reduced and its oxidation number next to it below the chemical equation. [20 points]

a.  CH4  +  O2  →  CO2  +  H2O

b.  Cu  +  Zn(NO3)2  →  Cu(NO3)2  +  Zn

c.    redox Rx

d.  NH3  →   N2  +  H2

e.  H2  +  O2  →  H2O2  (hydrogen peroxide)

2. In an electroplating experiment, a carbon and copper electrodes were put into a copper (II) nitrate solution and connected to a 25 mA current source.  How much time, in seconds, would be needed to plate 275 mg copper onto the carbon electrode ?  [10 points]

3.  Sketch the electrochemical cell in problem # 2 above; rationale / basis of your sketch.  Label the positive / negative pole of the battery and the copper / carbon electrode.  [10 points]

4.  What’s the pH of 175 mL of 25 mM CH3NH2 and 45 mM CH3NH3Cl  ?  [10 points]

5. In a buffer containing benzoic acid and sodium benzoate, write the net ionic equation that describes how this buffer would neutralize the addition of __.  [10 points]

a. Hydrochloric acid

b.  Potassium hydroxide

6. What’s the pH of a 125 mL solution of 25 mM benzoic acid and 75 mM sodium benzoate after the addition of  ___ ?  [20 points]

a. 15 mL of 10.0 mM HCl

b.  15 mL of 10.0 mM KOH