Ch. 17 & 20. equilibrium II & electrochem [85 points] AP Chemistry

For problems involving calculation, show your work in an organized manner, which includes any relevant equation / formula, proper units in your work / answer, and the proper number of significant figures in your answer.

1. A copper electrode and zinc electrode are put into an aqueous solution of zinc nitrate, which is connected to a battery such that the copper electrode is plated by zinc. [20 points]

a. sketch the electrochemical cell; label the cathode & anode; label the positive & negative terminals of the battery; identify the half-reaction at each electrode.

b. If the current is 525 mA and its duration is 25 minutes, what is the mass of zinc plated onto the copper electrode ?

2. Balance the following redox reaction, which occurs in a basic solution: [10 points]

Ag  +  CN ^-  +  O₂  -->  Ag(CN)₂ ^-

3. Is the following redox reaction

Cr₂O₇ ^2-_(aq)  +  H ⁺_(aq)  +  I ^-_(aq)  -->  Cr ⁺³_(aq)  +  I_2(s)  +  H₂O _(l)

at 37 °C spontaneous ? Justify your answer. [15 points]

4. 1.0 mM HA, a weak acid, has a pH = 4.6. What is the K _a of the acid ? [10 points]

5. What is the pH of a 100. mL 10.0 mM benzoic acid solution, after adding 10.0 mL of a 30.0 mM KOH ? [15 points]