4.1.1 (conductance) (conductivity)

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Conductometry 1 ก 4.1 ก ก ก กก ก ก ( ) 4.1.1 (conductance) (conductivity) ก ก (conductance, G) (Mho, Ω -1 ) (siemen, S) ก ก ก ก (molten salts) ก ก ก (aqueous solution) ก ก ก 4.

1 Conductometry 1 ก 4.1 ก ก ก กก ก ก ( ) (conductance) (conductivity) ก ก (conductance, G) (Mho, Ω -1 ) (siemen, S) ก ก ก ก (molten salts) ก ก ก (aqueous solution) ก ก ก 4.1 flow through cell ก (area, A) ก ก (distance, d) (a) (b) (c) (d) 4.1 : (a) dip type cell, (b) individual wands for titration, (c) fill type cell (d) flow through cell [Willard et al, Instrumental methods of Analysis, 1974]

2 Conductometry 2 ก ก dimension ก specific conductance (conductivity, κ) κ = Gθ = G*(d/A) θ cell constant ( cell) θ = d/a κ S cm -1 θ geometry ก ก กก conductance conductivity KCl κ Specific conductance conductivity KCl ( M ) ก KCl (S.cm -1 ) 18 o C 20 o C 25 o C X X X X X X X X X X X X 10-1 conductivity ก conductance ก ก θ A d G = κ/θ = (κa)/d conductivity ก ก ก

3 Conductometry 3 ก (charge, z) (size radius, r) (viscosity, η) (temperature,t) ก ก ก (solvation) ก ก ก (effective charge) ก ก mobility (u) ก u = ( z e) / (6πη r) e 1 (elementary charge constant) conductivity conductivity ก mobility ก κ = F Σ i z i u i C i F Faraday constant (96485 C/mol) i i, C mol/cm 3 ก ก ก 3 (1) ก ก (2) κ ก ( & mobility) (3) κ ก κ ก (total ionic concentration) ก ก (molar conductivity, Λ) ก (molar conductivity) molar conductivity (Λ) ก Λ = 1000κ/C C (mol/dm 3 ) (ก molar conductivity counter ion ก ) Λ S cm 2 /mol

4 Conductometry 4 molar conductivity 0.1 M KCl 1 M KCl ก ก molar conductivity ก ก ก ก (ionization) ก molar conductivity กก molar conductivity ก molar conductivity KCl CH 3 COOH ก molar conductivity ก ก ก ก ก (strong electrolyte) KCl, NaCl molar conductivity ก ก (weak electrolyte) CH 3 COOH molar conductivity ก ก ionization or dissociation ( ก ก ) ก กก effective charge

5 Conductometry 5 ก ก ก limiting molar conductivity (Λ 0 ) ก molar conductivity infinite dilution ก ก y ก 4.2 กก fitting กก ก ก Kohlrausch s law: Λ = Λ 0 K C 1/2 K ก electrolyte 1:1 (MA) 2:1 (M 2 A) ก ก (ionic molar conductivities) ก Λ 0 electrolyte Λ 0 ก cations anions Kohlrausch s law of independent migration of ions: Λ 0 = ν + λ ν - λ 0 - ν + ν - stoichiometric coefficients cations anions K 4 Fe(CN) 6 ν + = 4 ν - =1 4 K Fe(CN) 6 λ 0 + λ 0 - ก limiting ionic molar conductivities ก Handbook ก ก 25 0 C 4.2 temperature coefficient (α) α = (1/λ 0 I) (d λ 0 I /dt) 0.02 deg -1 λ 0 I,T = λ 0 I, 25o C [1 + α(t 25 o C)] [4] limiting ionic molar conductivities ก ก ก ก ก ก ก ( 4.3)

6 Conductometry limiting ionic molar conductivities 25 0 C [L. Coury, Current Separations, 18:3 (1999) 91-96]

7 Conductometry ก ก ก ก ก 1. ก ก ก ก / ก ก ก ก 2. ก ก ก ก ก ก ก ก ก ก electrical double layer capacitance ก ( 2) ก ก ก ก ก ก electrical double layer ( 1000 Hz ) 4.3 ก double layer capacitance ก ก migration

Conductometry 8 4.2.1 ก Wheatstone bridge Wheatstone bridge กก ก null point detection 4.4 ก ก ก 2 ก galvalometer EF ก 1. V AC = V BD ก 2. V EC = V FC ก G ( null point ) 3.

8 Conductometry ก Wheatstone bridge Wheatstone bridge กก ก null point detection 4.4 ก ก ก 2 ก galvalometer EF ก 1. V AC = V BD ก 2. V EC = V FC ก G ( null point ) 3. R 1 = R 2 null point ก R s ก R x R x ก scale potentiometer R s ก ก 4.4 Wheatstone bridge ก operational amplifier ก null point detection operational amplifier 4.5 ก ก E in op amp ก ก E o R f E o I x G x 4.5 operational amplifier: E o = E in (R f /R x + 1) = E in (R f G x +1)

9 Conductometry Contactless conductivity detection (CCD) กก Contactless conductivity detection Contactless capacitive coupling conductivity detection ก capillary ก กก 4.6 ก capillary ก dielectric ก ก capacitor 2 ก ก ก 2 gap R 1 R 2 ก ก potential divider apply ก ก ก R 1 R 2 ก R 1 ( ก ก ) R 1 ก ก R 2 ก operational amplifier (Op Amp) ก capacitor ก ก ก (rectify) ก ก ก ก 4.6 Contactless conductivity detection ก ก capillary ก ก ก ก ก capillary MΩ/cm gap R 1

Conductometry 10 gap 1 mm R 1 2-4 MΩ R 2 10 KΩ V R2 0.2-2 mv Vpp = 7 V 4.2.3.3 ก 1.

fit ก capillary ก (0.1.) capillary ก silver glue ก ก ( 4.7) 4.

10 Conductometry 10 gap 1 mm R MΩ R 2 10 KΩ V R mv Vpp = 7 V ก 1. - ก capillary tube - conducting paint (silver) capillary tube air gap electrode ก capillary capillary ก electrode - ก ก electrode fit ก capillary ก (0.1.) capillary ก silver glue ก ก ( 4.7) 4.7 CCD: a = capillary tube, b = electrodes c = detection gap - planar electrode planar chip electrode anti-parallel ก ก capacitive coupling ก electrodes ( 4.8) 2. Voltage source commercial function generator V pp frequency LC oscillator IC NE 555 Timer IC

Conductometry 11 4.8 CCD electrode ก 3. detection circuit: ก ก 4 ก 1. I-V converter ก ก 2.

11 Conductometry CCD electrode ก 3. detection circuit: ก ก 4 ก 1. I-V converter ก ก 2. rectifier ก ก 3. amplifier 4. offset adjustment ( 4.9) 4.9 Block diagram ก detection circuit CCD 4. ก / ก

12 Conductometry ก ก ก ก ก ก ก ก ก (conductimetry) ก ก ก ก ก ก (conductometry) ก ก ก ก ก ก ก ก ก ก ก ก ก ก ก ก ก ก ก ก ก / ก ก ก ก ก ก ก ก H 2 O = H + + OH - ; Kw = conductivity (K) 25 o C ก K = 10-7 mol/l (349.6 S.cm 2 /mol) mol/l (199.1 S.cm 2 /mol) = 10-7 /1000 mol/cm 3 (349.6 S.cm 2 /mol) /1000 mol/cm 3 (199.1 S.cm 2 /mol) = x S/cm 54.9 x 10-9 S/cm 55 ns/cm (~ 18 MΩ/cm) ก conductivity ก ก ก

13 Conductometry ก ก ก conductivity ก ก ก (interested site) ก (control site) site ก / / ก ก conductivity ก ก ก กก ก ก conductivity ก ก ก ก conductivity ก ก ก (remote monitoring ) ก ก ก [10] ก : P, pump; L, water level sensor; DO, dissolved oxygen probe; C, conductivity probe; ph, ph probe; PLC, program logic control; FIA, flow injection analyzer for determination of iron, sulfate and phosphate; MR, mobile radio; M, modem; PC, personal computer. [W. Kunawanakit et al, Lab Robotics and Automation, 12 (2000) 164]

14 Conductometry ก ก ก ก (sensitivity) (selectivity) ก ก ก ก กก ก ก ก (ion chromatography) (capillary electrophoresis) ก ก ก ก ( universal detector) CCD ก ก ก capillary electrophoresis ก ก cations anions ก ก ก ก ก electropherogram ก ก CE CCCD ก UV [Anal. Chem., 70 (1998) 4339] CCD 1. ก (no galvanic contact) ก ก ก

15 Conductometry ก ก cations anions ก spectrophotometric detector 3. ก spectrophotometric detector ก background electrolyte (BGE) ก 4. ก ก ก CCD ก ก ก ก ก detection window spectrometer 5. ก ก CE capillary ก ก ก ก ก ก ก gas diffusion membrane, pervaporation ก ก ก ก ก acceptor stream (R2) 4.12 ก ก ก [Anal. Chim. Acta, 363 (1998) 199]

16 Conductometry ก ก ก ( ) 3 [Talanta, 49 (1999) 1023] ก ก ก ก ก ก ก ก ก ก ก ก ก ก ก ก ก ก ก ก ก λ 0 ก ก (interpret) ก ก HCl NaOH ก H 2 O NaCl ก titration curve 4.13 ก λ O (S.cm 2 /mol) H + (349.6), Cl - (70.3), Na + (50.1) OH - (199.1) ก ก ก ก H + Cl - ( =419.9) NaOH OH - ก ก H + H 2 O ก H + Na + ก (Na + Cl - = = ) OH - ก ก ก Na +, Cl - OH - ก ก ก ก

17 Conductometry ก ก ก ก ก ก ก (selectivity) ก ก ก ก ก ก ก ก ก ก ก ก (critical micelle concentration) ก ก vesicle ก ก ก ก ก paper ก ก ก ก ก ก ก 3. paper

Unit - 3 ELECTROCHEMISTRY VSA QUESTIONS (1 - MARK QUESTIONS) 3. Mention the purpose of salt-bridge placed between two half-cells of a galvanic cell?

Unit - 3 ELECTROCHEMISTRY VSA QUESTIONS (1 - MARK QUESTIONS) 3. Mention the purpose of salt-bridge placed between two half-cells of a galvanic cell? Unit - 3 ELECTROCHEMISTRY 1. What is a galvanic cell? VSA QUESTIONS (1 - MARK QUESTIONS) 2. Give the cell representation for Daniell Cell. 3. Mention the purpose of salt-bridge placed between two half-cells