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Transport in electrolyte solutions Sähkökemian peruseet KE Tanja Kallio C213 CH 3.1 – 3.2

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Ion distribution in the bulk and near the surface J. Israelachivili, Intermolecular and surface forces Spatial distribution of ions obeys Boltzmann distribution

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Transport and reactions electrode i) mass transfer ii) adsorption iii) (electo)chemical reaction e-e- electrolyte Cu 2+ + e Cu + iv) desorption v) mass transfer r = reaction rate J i = flux of i

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Transport and mobility FfFf FcFc v charged particle in an electric field (F c ) Einstein mobility F f = friction force q = charge of the particle E = electric field v = velocity D = diffusion coefficient u = mobility q

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Mobility, molar conductivity and diffusion coefficient Ohms lawadapted Faradays law from previous slide Stokes law can be applied to determine friction coefficeint for ions = viscosity a = ion radius

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Walden rule K + () Cs + ()

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Measuring conductivity johto- kyky- mittari Exchange current Pt-electrodes calibration

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Electronic vs. ionic conductivity ich_metals_are_the_most_co nductive#ixzz25OZd6XAR Electronic conductivity: current is transported by electrons i) conductors ii) semi conductors iii) insulators Ionic conductivity: current is transported by ions i) strong electrolytes ii) weak electrolytes iii) non electrolytes MaterialCond / S cm -1 Ag1.59×10 5 Cu1.68×10 5 Au2.44×10 5 Pt1.06×10 4 C (amorphous)5-8×10 1 C (graphite)* ×10 3 / 3.0×10 1 Ge4.6×10 2 Si Water10 -9 Glass PTFE (Teflon ® )

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Structure, mobility Ca 2+ i ii iii Proton transport via Grothus or hopping mechanism

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Strong electrolytes - Kohlrauschs law (1/2) Dependency of diffusion coefficient on concentration Debye-Hückel limiting law for 1:1 electrolytes Using above diffusion coefficient can be written as B = A

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Strong electrolytes - Kohlrauschs law (2/2) Kohlrauschs law

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Weak electrolytes – Ostwald dilution law (1/2) is small ± ~ 1. So for 1:1 electrolytes

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Weak electrolytes – Ostwald dilution law (2/2) Combining this with rearranged equation for equilibrium constant for 1:1 electrolytes Ostwald dilution law c + and c - are low + ~ +, and - ~ -,

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Comparison of a weak and a strong electrolyte guide.blogspot.fi/2010/04/vari ation-of-conductivity- with.html KCl

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Electrolyte dissociation in an organic solvent Dissociation is incomplete Ostwald dilution law Because of interactions ± must be included For 1:1 electrolytes It has been noted experimentally that tetrabutyyliammoniumtetrakis (4-klorofenyyli)borate in 1,2- diklooriethane

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