Chem 143-013

TA: Daniel Willems

Student: Christoffer Renner (Lab partner: Patrick Murphy)

An Introduction to ElectrochemistryApril 18 th , 2012

Part I:

According to my table the zinc half-cell reaction has the greatest tendency toward reduction and the nickel half-cell reaction has the greatest tendency toward oxidation. Based on the table constructed on pg. 94, the copper/zinc cell should have a voltage of -0.05 V. Measured voltage was -0.08 V. This is 60% greater than expected.

Part II:

Note that for my Ecell(calc), I assumed that Eocell(calc) was equal to our previously measured value of -

0.08 v instead of the value of 1.10 V suggested by the lab manual. My Ecell(calc) values differed from my Ecell(measured) values more than 100% at times, but worst than that the trend on my measured values was opposite of my calculated values (going to a smaller negative voltage with decreased concentration instead of going to a larger negative voltage with decreased concentration as predicted). I think this difference in trend is do to the fact that these cells should be reading a positive voltage which would make the trends both decrease in magnitude with decreasing concentration.

Part III:

The solution turned a dark purple around the black electrode (the anode in this case) and turned orange around the red electrode (the cathode in this case).

Part IV:

The Standard Reduction Potential Table on OWL gave voltages that were as follows:

Cell Chemistry: Tables predicted voltage (V) Measured voltage (V)Pb/Zn -0.637 0.47Pb/Cu 0.463 0.42Pb/Ni -0.124 -0.23

The measured and predicted voltages are significantly different primarily for the Pb/Zn cell which has the wrong sign. This is possibly do to an incorrect solution (maybe it’s not really zinc). Other sources of error are cross contamination between solutions and poor electrical connections between wires and electrodes.

Part V:

The slope of the line is -0.0269. This is equal to -2.303*RT/n at 298K and n = 2. The slope of the line should be equal to -2.303*RT/n at 298K and n = 2. The y intercept is -0.0801. This is supposed to be equal to Eo

cell and it is equal to what we measured (because I used this value for Eocell in my calculation).

-1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5

-0.18

-0.16

-0.14

-0.12

-0.1

-0.08

-0.06

-0.04

-0.02

0

f(x) = − 0.0296 x − 0.0801

Ecell vs. log([Zn]/[Cu])

Log([Zn]/[Cu])

Ecel

l