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AP Chem Lab 10 Electrochem Lab Report.docx

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CHEM 1951

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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