Curt Kim, Jonathan Lee, Keshav Mantha, Bobbie Sheng
AP Chemistry, Period 1
4/23/13
Title: Electrochemistry Lab
Goal: To measure the voltage of two voltaic cells, one with standard concentrations and the
other with non-standard concentrations, and compare the readings to the calculated theoretical
voltages
Procedure: There were two parts to this experiment: Part A, a standard voltaic cell with 1.0M
CuSO4 and 1.0M Zn(NO3)2, and Part B, a non-standard voltaic cell with 0.5M CuSO4 and 0.5M
Zn(NO3)2. In Part A, 75mL of the 1.0M copper sulfate solution and 15mL of the 1.0M zinc
nitrate solution were prepared. The zinc nitrate was poured into the smaller, semipermeable
compartment of the voltaic cell and copper sulfate was poured into the outer jar. Then, the
copper electrode was clipped into place in the copper sulfate solution, and the zinc electrode was
placed in the zinc nitrate solution. A voltmeter was then used to take a voltage reading of the
cell. Part B used the same voltaic cell setup and experimental procedure, but the concentrations
of the solutions were decreased to 0.5M by adding equal amounts of water as the original amount
of 1.0M solution available and then pouring out the final amounts required for the cell.
Data:
Standard Cell Non-Standard Cell
Concentration of CuSO4 1.0M 0.5M
Concentration of Zn(NO3)2 1.0M 0.5M
Measured Voltage 0.89 V 0.844V
Data Analysis:
Reduction Potentials:
Cu2+ + 2e- → Cu +0.34V
Zn2+ + 2e- → Zn -0.76V
Cu2+ has a higher reduction potential, so Cu2+ is reduced and Zn is oxidized. Therefore, the
copper strip was the positive cathode and the zinc strip was the negative anode.
Balanced Net Ionic Equation: Cu2+ + Zn → Cu + Zn2+
Calculated Electron-Volt Potential for the Standard Cell:
Voltage = Reduction Potential of the Cathode’s Reaction - Reduction Potential of the Anode’s
Reverse Reaction = +.34V - (-.76V) = 1.10V
Percent Error for the Standard Cell:
Percent Error = | Theoretical Value - Experimental Value | / Theoretical Value * 100% =
| 1.10 - .89 | / 1.10 * 100% = 19.091%
Calculated Electron-Volt Potential for the Non-Standard Cell:
E = E՞ - (.0257V/n)lnQ = 1.10V - (.0257V/2)ln([Zn2+]/[Cu2+]) = 1.10V -
(.0257V/2)ln(0.5/0.5) = 1.10V
Percent Error for the Non-Standard Cell:
Percent Error = | Theoretical Value - Experimental Value | / Theoretical Value * 100% =
| 1.10 - .884 | / 1.10 * 100% = 19.636%
Discussion:
1. Both the standard cell the and non-standard cell were about 20% under the expected value.
2. Within the cell, the concentrations of the solutions may have been slightly off, and the
electrodes may have contained impurities or actually been alloys.
3. The cranking power of a car is measured in Cold Cranking Amps, or CCAs, which are defined
as the amount of current (in amperes) a car battery can deliver for a 30-second period at 0ºF until
the battery voltage drops too low to be used. As temperature drops, the cranking power of a car
increases. This makes sense because of the formula P = IV, which can be rearranged as I = P/V.
V = (RT*lnQ)/(Fn) by the Nernst equation, so lowering temperature would reduce voltage and,
therefore, increase current. As more c

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