Ch. 17 equilibrium II &  ch. 20 electrochemistry                     75 points                                   AP chemistry

In problems involving any calculation, 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.

1. Write the net ionic equation to describe the mechanism how a buffer containing potassium lactate and lactic acid responds to the addition of __.  [10 points]

a. Strong acid

b.  Strong base

2.  The addition of sodium carbonate to a 75 mL aqueous solution containing 1.0 mM copper (II) nitrate and 5.0 mM barium nitrate forms a precipitate.  For simplicity, assume that the addition of sodium carbonate does not change the volume of the aqueous solution; what the first precipitate ?  justify / rationalize your answer.  [10 points]

3. What is the pH of 75 mL 5.0 mM lactic acid after the addition of __.  [20 points]

a.  24.0 mL of 15.0 mM potassium hydroxide

b. 5.0 mL of 0.1 mM hydrochloric acid

4.  Sketch the voltaic cell contains zinc nitrate and a zinc electrode and copper (II) nitrate and a copper electrode.  [20 points]

a. label the solution and the electrode in the solution

b. what is the redox reaction ?  show / justify that it’s a thermodynamically feasible reaction under standard conditions.

c. What is the half-reactions associated with each electrode ?

i. Zinc:  ___________________________________

ii.  Copper:  ________________________________

d.  Redraw / label the electrochemical cell and show the direction of the electrons in the circuit and the ions in the salt bridge.

5. How much time, in minutes, would be needed to generate 75 mL of oxygen gas at 25 °C with a pressure of 95 kPa in the electrolysis of water using a 250.0 mA current source ?  [15 points]