Review- Electrochemistry

How it works

• Partner “green” will discuss a strategy on how to complete the problem

• Then, Partner “blue” will comment on the strategy and add any further details needed and write down the steps to solving the problem, without actually solving it.

• Finally, Partner “red” will use the strategy that the other two partners outlined to actually complete the problem.

• Roles will be rotated each problem

Problem 1 (Blue, green, red)

• How many grams of aluminum can be deposited if 31,500 coulombs of electricity pass through an aluminum nitrate solution?

answer

• 2.94 grams

Problem 2: (green, red, blue)

• Balance the following equation

AsH3 + ClO3- H3AsO4 + Cl- (acidic soln)

answer

• 3 AsH3 + 4ClO3- 4Cl- + 3H3AsO4

Problem 3 (red, blue, green)

• If 10.0 amperes of current flow for 20.0 minutes through a solution of copper (II) nitrate, how many moles of copper are deposited?

answer

• 0.062 moles

Problem 4: (red,blue,green)

• Water was electrolyzed for 5.61 minutes using a constant current of 0.513 amperes. Calculate the volume, in liters, of hydrogen gas produced at 298 K and 1.00 atm.

answer

• 0.022 L

Problem 5

• Calculate Ecell for the reaction that occurs when a standard voltaic cell of Zn/Zn2+ and Al /Al3+ have concentrations of 0.100 M and 0.0500M respectively.

answer

• 0.896 V

Problem 6: (red, green, blue)

• 5.77 g of zinc is deposited at the cathode when a current of 7.1 amperes passes through an electrolytic cell for 40. minutes. What is the oxidation state of the zinc in the aqueous solution?

answer

• Zn 2+

• Should find that there are 0.088 moles of Zn and 0.17658 moles of electrons- which must mean that there need to be 2 moles of electrons per mole of Zn meaning that the oxidation state is 2.

Problem 7:

• Balance the following reaction:

N2O4 + Br- NO2- + BrO3

- (basic soln)

answer

• Br- + 6OH- + 3 N2O4 6 NO2- + BrO3- + 3H2O

Problem 8: (green, red, blue)

• Choose the best reducing and oxidizing agent from the following:– Cu(s)– Zn(s)– Ag+

– Al3+

– F- – F2

answer

• Strongest oxidizing agent: F2 (it itself is reduced)

• Strongest reducing agent: Zn (it itself is oxidized)

Problem 9: (red, blue, green)

• All of the following substances can act as oxidizing agents except:a. H2O2

b. Cr2O7 2-

c. MnO4 –

d. IO3 –

e. Br –

answer

• Br-

Problem 10: (blue, red, green)

• Calculate K(the equilibrium constant) at 298K for the following reaction:

Cl2 (g) + 2I- (aq) 2 Cl-(aq) + I2(s)

answer

• E⁰=0.83V • K=1.2x1028 or 1.1x1028