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Name . . . . . . . . . . . . . . …......... Lab Section. . . . . . . . . . . TA . . . . . . . . . .. . …… . . .Date . . . . . . . . . Group Members . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lab Section . . . . . . . . . . . . . . . . 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 =�__________________ ����������������������� 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?