Transport in electrolyte solutions

1. Transport in electrolyte solutions Sähkökemianperuseet KE-31.4100 Tanja Kallio tanja.kallio@aalto.fi C213 CH 3.1 – 3.2

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

3. Transport and reactions electrolyte electrode i) mass transfer Cu2++ eCu+ ii) adsorption e- r = reaction rate Ji = flux of i iii) (electo)chemical reaction iv) desorption v) mass transfer

4. v Ff Fc Transport and mobility charged particle in an electric field (Fc) Einstein q mobility Ff = friction force q = charge of the particle E = electric field v = velocity D = diffusion coefficient u = mobility

5. Mobility, molar conductivity and diffusion coefficient Ohm’s law adapted Faraday’s law from previous slide k Stokes’ lawcanbeapplied to determinefrictioncoefficeint for ions h = viscosity a = ion radius

6. Walden rule K+(●) Cs+(■)

7. johto-kyky-mittari Measuring conductivity • Exchange current • Pt-electrodes • calibration

8. Electronic vs. ionic conductivity 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 http://wiki.answers.com/Q/Which_metals_are_the_most_conductive#ixzz25OZd6XAR

9. Structure, mobility Ca2+ i Proton transport via Grothusor hopping mechanism ii iii

10. Strong electrolytes - Kohlrausch’slaw (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 = 2.303 A

11. Strong electrolytes - Kohlrausch’s law (2/2) Kohlrausch’s law

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

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

14. Comparison of a weak and a strong electrolyte KCl http://chem-guide.blogspot.fi/2010/04/variation-of-conductivity-with.html

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