Exp2 Avogadro's Number

7/22/2019 Exp2 Avogadro's Number

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Exp 2. Determining Avogadros Number(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 onemole
http://upload.wikimedia.org/wikipedia/commons/8/88/M_Faraday_Th_Phillips_oil_1842.jpg


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> ApparatusDC source, insulated copper wires,timer, barometer, 50mL buret, 250mL beaker, ruler, thermometer

> Chemicals3M H2SO4 (Caution!)

Continue 150~300 mA

Q(c) = I(A) t(s)

ObjectiveTo determine the values for the faraday and Avogadros

number by Electrolysis


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1. In a 250mL beaker, add 100mL of distilled water and then 50mLof dilute (3M) sulfuric acid.

100 mL Water+ 50mL H2SO4 (total 150mL)

2. Fill a 50 mL buret with this solution and invert it in the solution

Invert

Stir it with a glass rod

Procedures


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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 theDC source. And place the other end uninsulated into theinverted mouth of the burette.

(-)

(+)


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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

measured1) Record the time, turn on the DC source, and record the ammeterreading (It is important to maintain a steady current)

2) Continue the electrolysis until at least 20mL of hydrogenhasbeen collected. 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 thebarometric pressure and the vapor pressure of water at thesolution temperature.


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PH2

= Pbarometric- PH2

OcolumnPH2

O vapor

PH2O column= (height of H2O in mm) / (13.6mm H2O/mmHg)

PV = nRT We can find out the Moles of H2 produced.

Q(c) = I(A) * T(s) We can also find out number of coulombs passed

Electron numbers =

Avogadros number N(electron/mol)

2H+ + 2e- H2 ne- (moles) = 2 nH2 (moles)

9.

15.

1F (C/mol e-) =ne-(mol)

The number of coulombs(C)

16.

The number of coulombs(C)

1.610-19 C/e-

ne-(mol)

N (e-/mol) =

Calculation


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Additional Usage Notes


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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

Fast-Release Pipette Pump
http://www.opticsplanet.net/picture-1-bel-art-vwr-fast-release-pipette-pump-ii-pipetting-devices-379111010.html


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Safety Wide Mouth Wash

Bottle

Labeled Water with BlueCap

Use Distilled Water ONLY

Labeled Acetone with RedCap

Use Acetone ONLY

Documents

Exp2 Avogadro's Number