Experimental Determination of the Faraday

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Experimental Determination of the Faraday
2
Experimental Objective

• Determine the value of the Faraday (charge on one
  mole of electrons)
• Determine the molar mass of Cu

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Procedure Overview

• Copper oxidized by acid (Electrolysis)
• Cu(s) 2H(aq) ? Cu2(aq) H2(g)
• Not spontaneous
• External electrical force applied
• Product hydrogen gas collected
• Pressure, volume and temperature of collected gas
  determined.
• Magnitude and duration of current measured.

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Electrolysis of Cu by Acid

• Cu(s) 2H(aq) ? Cu2(aq) H2(g)
• Anode Cu(s) ? Cu2(aq) 2e-
• Cathode 2H 2e- ? H2(g)

Electron flow from anode to cathode External
source of electrons removes electrons from anode
which becomes positive () forces electrons to
cathode which become negative (-) Note In a
spontaneous electrochemical cell the anode is (-)
and the cathode is () and electrons
spontaneously flow from (-) to ()
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Procedure DetailsPrepare Cu electrode (anode)

• Work in Pairs
• Obtain copper sheet sample
• Clean copper electrode
• Sand
• Rinse
• DRY
• Record mass of copper electrode

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Procedure DetailsPrepare Gas Buret for gas
collection

• Fill largest beaker slightly more than 1/2 full
  of water
• Add 3M sulfuric acid to beaker
• Completely fill buret with dilute sulfuric acid
  solution. No air!
• Invert and submerge in beaker.
• Wash hands after submersion in dilute acid.

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Procedure DetailConnect External Force

• Labworks
• Page 163 of lab manual
• Use clean cathode
• Make good connections
• Position electrodes close together
• Obtain instructor approval

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Procedure DetailsOxidize the Cu and collect the
H2

• Apply external force (page 164)
• Collect minimum of 40 mL hydrogen gas

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Procedure DetailsRecord Data

• Record the temperature of the water -thermometer
• Record the atmospheric pressure provided by
  instructor
• Record the volume of gas collected gas buret
• Record the height of the column of water
  remaining in the buret above the water surface in
  the beaker meter stick

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Procedure DetailRecord Data from Labworks

• See page 164
• Total time of applied current
• Average magnitude of current
• Ohms Law current voltage/resistance
• amps V/ohm
• Resistance used 1 ohm

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Procedure Details

• Repeat Procedure
• Clean-up and begin Check-out Procedure
• Refer to Handout
• Complete Data Analysis while waiting for
  instructor check-out

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Waste Handling

• Dispose of liquid waste in supplied liquid waste
  container
• Be careful to not overflow the waste container

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Data AnalysisPressure of Gas collected
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Data AnalysisMoles of Gas collected
Pressure of collected hydrogen
gas, atm (calculated) (Phdyrogen gas,
mm Hg)(1 atm/760 mm Hg) Volume
of collected hydrogen gas (buret reading) T
Temperature in degrees K (read from thermometer
and converted) R Gas Constant 0.0821
L-atm/mole-K
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Data Analysis FaradayCharge on one mole of
electrons
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Data AnalysisMolar mass of Cu From Charged
Transferred

• Moles of Cu reacted

• Molar Mass mass to mole ratio

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Data AnalysisMolar mass of Cu From Hydrogen Gas
Collected

• Moles of Cu reacted Moles of H2 collected

• Molar Mass mass to mole ratio

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Final Exam

• Date Tuesday May 3
• Time 800 AM
• Location Consult Instructor
• Please note that due to the large number of
  students involved in this exam the above time is
  the ONLY time the exam will be given. You MUST
  be present on 5/3 at 800 AM.