Lab 11 - Lab report discussing voltaic cells PDF

Preview

Summary

Lab report discussing voltaic cells...

Description

3150:154:003 Experiment 11: Voltaic Cells. Using Redox Reactions to Do Work April 6th, 2017 Objective The objectives of this experiment are to construct five voltaic cells and find the measurements of the corresponding cell potentials, as well as compare these to the theoretical cell potentials. Procedure A LabQuest Handheld and one 30-mL beaker was checked out of the stock room. Using Table 1, the correct volumes of stock zinc, stock copper and stock silver was filled. Five Voltaic cells were set up properly, using the procedure given on pages 103-104 of the Chemistry Lab Manual. Sample Calculations Calculation of Standard Cell Potential (Equation 4) E°cell= E°reduction(cathode) + E°oxidation(anode) E°cell= 0.34 - 0.80 E°cell= -0.46

Calculation of cell potential using Nernst Equation (Equation 5) Ecell = E°cell - (RT/nF)lnQ -0.42 V = E°cell - (8.314 JK-1mol-1)(293.9K) / (1 mole) (96485 Cmol-1) ln (2) -0.42 V = E°cell - (0.02533)

E°cell = 0.69 Results Data and Observations Using Table 1, the proper amounts of stock copper, stock zinc and stock silver were distributed for the experiment. Fifteen milliliters of stock copper was used, while 25 mL of stock zinc and stock silver was used. For voltaic cell one, the voltage was found to be 0.894 V, with the temperature at 293.9 K. The voltage of voltaic cell 2 was found to be 0.297 V, with the temperature at 293.9 K. For voltaic cell 3, the voltage was found to be -0.406 at 293.9 K. For voltaic cell 4, the voltage was found to be -0.399 V with the temperature at 294.15K. For voltaic cell 5, the voltage was found to be 1.275 K The reduction voltage values for both the cathodes and anodes are provided in table 2. Tables

Voltaic Cell

Anode Reaction

Cathode Reaction

Cell 1

Zn (s) → Zn2+(aq, 0.100M) + 2e-

Cu2+(aq, 0.100M) + 2e-→ Cu(s)

Cell 2

Zn(s) → Zn2+(aq, 0.050M) + 2e-

Cu2+(aq, 0.100M) + 2e-→ Cu(s)

Cell 3

Ag+ (s) → Ag+(aq, 0.100M) + 1e-

Cu2+(aq, 0.100M) + 2e-→ Cu(s)

Cell 4

Ag+ (s) → Ag+ (aq, 0.050M) + 1e-

Cu2+(aq, 0.100M) + 2e-→ Cu(s)

Cell 5

Zn(s) → Zn2+(aq, 0.100M) +2e-

Ag+(aq, 0.050M) + 1e- → Ag(s)

Table 1. Half Reactions in the Five Voltaic Cells.

Voltaic Cell

Balanced Cell Reaction Equation

E°red (cathode) ( E°red (anode) V) ( V)

E°Cell (V)

Cell 1

0.34 Zn(s) + Cu2+ (aq)→ Zn2+(aq) + Cu(s)

-0.76 ( - ( -0.76) ) = +0.76

0.42

Cell 2

2 Zn(s) + Cu2+ (aq) → Zn2+(aq) + 2Cu (s)

0.68

1.52

0.92

Cell 3

Ag+(s) + Cu2+ (aq) → Ag2+(aq)

0.34

0.80 ( - (0.80) ) = -0.80

-0.46

+ Cu(s) Cell 4

2Ag+(s) + Cu2+ (aq) → Ag2+(aq) + 2Cu(s

0.34

1.6

-1.26

Cell 5

Zn2+(aq) + 2Ag+ (aq) → 2Zn(aq) + Ag2+(aq)

0.80

0.76

0.04

Table 2. Worksheet 1 Equivalent for Theoretical Expectations for the Voltaic Cells Under Standard Conditions.

Voltaic Cell

E°Cell ( V)

T (K)

n

Q

ln(Q)

E°Cell (Calculat ed)

E°Cell (V) (measure d)

Cell 1

-0.42

293.9

1

2

0.69

0.69

0.894

Cell 2

0.92

293.9

2

2

0.69

0.91

0.297

Cell 3

1.14

293.9

1

2

0.69

1.12

-0.406

Cell 4

-1.26

294.15

2

2

0.69

-1.26

-0.399

Cell 5

0.04

294.15

2

0.5

-0.69

0.49

0.275

Discussion After the experiment concluded, the E° values were found to be -0.42 V, 0.92 V, 1.14 V,

-1.26 V and 0.04 V. The calculated E°cell values were 0.69 V, 0.91 V, 1.12 V, -1.26 V and 0.49 V. The measured E°cell values were found to be 0.894 V, 0.297 V, -0.406 V, -0.399 V and 0.275 V respectively. For voltaic cell 1, the calculated and measured values were found to be very close. However, for voltaic cells 2-4, the measured and calculated values were not very close. For voltaic cell five, the calculated and measured values were in the same range. Under standard conditions, the standard cell potential should equal the measured cell potential.

Cells 3 and 4 are negative because of the Nickel acting as the anode, instead of the zinc acting as the anode, even though they had the same molarities. For each of the voltaic cells, the higher the molarity, the lower the cell potential. Along with that, the lower the molarity, the higher the cell potential. Errors that could take place in this experiment, would be the salt bridge not soaking long enough. Another potential error would be the voltage probes being dipped into the solution along with the wires....