Exp 2' Electrolysis, the Faraday and Avogadro's number

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Exp 2. Electrolysis, the Faraday and Avogadro's
number

• Lab 406, 2 students

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Introduction

• Electrolysis of water
• Anode (oxidation) 2H2O (l) ? O2 (g)
  4H (aq) 4e-
• Cathode (reduction) 2H2O (l) 2e- ? H2
  (g) 2OH- (aq)
• Faradays constant
• F NA e ( NA Avogadros number
• e Elementary
  charge )
• Avogadros number
• Avogadro number is the number of atoms or
  molecules in one mole

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• Objective

To determine the values for the faraday and
Avogadros number by Electrolysis

• Apparatus
• DC source, insulated copper wires,
• timer, barometer, 50mL buret, 250mL beaker,
  ruler, thermometer

• Chemicals
• 3M H2SO4 (Caution!)

Continue 150300 mA
Q(c) I(A) t(s)
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• Procedures

1. In a 250mL beaker, add 100mL of distilled
water and then 50mL of dilute(3M) sulfuric acid.
2. Fill a 50 mL buret with this solution and
invert it in the solution

Invert
100 mL Water 50mL H2SO4 (total 150mL)
Stir it with a glass rod
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A square piece of paper (2.5cm X 2.5 cm)
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3. Attach the copper wire cathode to the negative
terminal of the DC source. And place the other
end uninsulated into the inverted mouth of
the buret.
(-)
()
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• Make sure that the bare anode put inside of
  burette.

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4. The volume of solution in the buret should be
accurately measured
1) Record the time, turn on the DC source, and
record the ammeter reading (It is important to
maintain a steady current)
2) Continue the electrolysis until at least 20mL
of hydrogen has been collected.
3) Note the time when the electrolysis is
stopped.
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5. Measure of the height of the water column in
the buret above the solution in your beaker.
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6. Measure the temperature of the acid solution
and obtain the barometric pressure and the vapor
pressure of water at the solution temperature.
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9.
PH2 Pbarometric- PH2Ocolumn PH2O vapor
PH2O column (height of H2O in mm) / (13.6mm
H2O/mmHg)
PV nRT
We can find out the Moles of H2 produced.
15.
Q(c) I(A) T(s)
We can also find out number of coulombs passed
2H 2e- ? H2 ne- (moles) 2 nH2 (moles)
The number of coulombs(C)
1F (C/mol e-)
ne-(mol)
16.

• Avogadros number N(electron/mol)

The number of coulombs(C)
Electron numbers
1.6 10-19 C/e-
N (e-/mol)
ne-(mol)
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Additional Usage Notes
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Fast-Release Pipette Pump
Fit pipet up to 25mL Flexible elastic
thermoplastic rubber chuck holds pipet snugly for
safe, sure use. -Simply insert pipet into
detachable, cone-shaped chuck with light finger
pressure -To fill, grasp pump in palm of hand
and rotate knurled wheel with thumb -To empty
rapidly, lightly press thumb on quick-release
lever -To empty gradually, rotate wheel -Parts
disassemble for maintenance
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Safety Wide Mouth Wash Bottle
Labeled Water with Blue Cap Use Distilled
Water ONLY
Labeled Acetone with Red Cap Use Acetone ONLY