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EXPERIMENT 6
Chemistry 0330 Laboratory Report 6
Part I How Can We Use a Hydrogen Fuel Cell to Generate Clean Energy and Connect
Chemistry to the Real World?
I. Describe the purpose of the experiment in a few sentences. You can use background information from the
introduction, but do not copy directly.
II. Summarize the experimental results.
a) Fill in the following table with your data.
Voltage (V)
1st time
2nd time
3rd time
Average
Open circuit
Fuel cell powering the
mini vibrating motor
0.1 Ω resistor
b) According to the Ohm’s law, use the average voltage of the 0.1 Ω resistor to calculate the average
current of the running circuit for the cell phone mini vibrator:
c) Fill in the following table with the parameters calculated or given from the question II. For electric
current or potential, use the average values from the measurements. Show all your work below the table
(hint: The current for an open circuit is zero).
Fuel cell potential Fuel cell power
Load
Current (A)
(V)
(Watts)
Open Circuit
Vibrating Mini
Motor
0
III. Calculate the following electric and thermodynamic parameters:
1. Calculate Horxn and Gorxn (in kJ/mole of H2) for the following fuel cell reactions from the standard
values of Hof and Gof (See Zumdahl Appendix four, or Tro Appendix II B).
H2 (g)+ 1/2 O2 (g)  H2O (l)
2. The overall hydrogen fuel cell reaction is H2 (g)+1/2 O2 (g)  H2O (l). Write down the two half
reactions and calculate the standard fuel cell potential, Eo (or open circuit potential), using their standard
half cell reduction potentials (See Zumdahl Appendix five, or Tro Appendix II D).
3. Calculate the following values for the consumption of one mole of H 2:
A)Maximum electric work (Wel max) under standard conditions using GOrxn from Question 1
B)Standard open circuit voltage, Eoopen, using GOrxn from Question 1
C)Maximum efficiency for a reversible fuel cell under the standard conditions using GOrxn and HOrxn
from Question 1
4. Calculate the maximum electric work (in kJ/mol of H2) using an experimentally measured open circuit
cell potential from the previous table assuming that only the reversible electrical work is performed at
constant temperature and pressure. Compare this with the Wel max calculated under standard conditions
using Gorxn from Question 3 and explain the difference.
5. Electrons moving at fuel cell potential, E (in unit of V), provide the electric work, W el (in J/mol of H2).
Suppose that the fuel cell output voltage is stable within a short period of powering the cell phone vibrator,
calculate the electric work done and efficiency
when it is running the cell phone
vibrator.
III. Discussion
Write a short response explaining one of the following questions (in less than 150 words):
i) Why can the efficiency (η, %) of a fuel cell hardly ever equal 100% in this experiment?
ii) List more than one difference between the electrolysis process used by a fuel cell and the electrolysis of
water in a beaker.
Part II How are Electrons Used to Electroplate and Generate Chemical Reactions?
1. Summarize the data for Part A:
Buret H
Void volume (Vo)
Volume of Gas (Vb)
Height of NaOH
column (h, mm)
Temperature, T (oC) ____________________
Barometric pressure, BP (inches Hg) ____________________
Buret O
Weight of copper cathode (g) ____________________ before electroplating
Weight of copper cathode (g) ____________________ after electroplating
Current at time intervals
Time (sec)
Current (amp)
Total time _______________ (sec)
2. Calculations: Electrolysis (Show calculations for each step.)
a. Correct for vapor pressure of water
Pw =_______________mm Hg
b. Convert barometric pressure to mm Hg
Pa =_______________mm Hg
c. Calculate pressure of hydrogen (Buret H)
Pg =_______________mm Hg
d. Calculate pressure of oxygen (Buret O)
Pg =_______________mm Hg
e. Calculate T (K)
T =____________________ K
f. Calculate the volume of hydrogen and oxygen at ambient temperature and pressure
Vt =�__________________ mL Hydrogen Vt =�________________�mL Oxygen
g. Calculate the moles of hydrogen
nH =�__________________
h. Calculate the moles of oxygen������������������������
nO =�__________________
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i. Calculate the mole ratio of hydrogen to oxygen in water
3. Calculations: Electroplating (Show all your work.)
a. Calculate the number of moles of copper that were plated
moles of Cu =_______________
b. Calculate the number of moles of electrons of copper
moles of electrons of Cu =_______________
c. Calculate the number of moles of electrons of O2
moles of electrons of O2 =_________________________
d. Calculate the average current
Current =_________________________ Amp
e. Calculate the total charge transferred
_________________________ Coulombs
f. Calculate the value of Faraday’s constant, the total charge per mole of electrons
F =q/mole electrons Cu
F =q/mole electrons O2
g. Calculate the % error between both experimental values in part f and the accepted value of the Faraday
constant of 96,485 C/mol.
h. Discuss the possible sources of error.
4. Summarize the data for Part B.
Mass of souvenir object ______________________________
Mass of souvenir object after electroplating ______________________________
Current at time intervals
Time (sec)
Current (amp)
Total time _______________ (sec)
Calculate the amount (mass in grams) of Cu plated by using the following equation: Current (Amp) x�
time(s) ×1 mol electron/96,485 C ×1 mol Cu/ ? mole electrons Cu ×molar mass (g/mol) of Cu =mass of Cu
(g) plated. (Show your work.)
Calculate the % error between the calculated mass of Cu electroplated and the directly measured mass.
(Use the directly measured mass as the denominator.)
Give a possible reason why the two values differ. Which do you believe is more accurate?