Ion Association Ion pair formation Ion Association Ion
- Slides: 29
Ion Association Ion pair formation
Ion Association Ion pair formation fully solvated solvent-shared or solventseparated Ion pair contact ion pair Ion pairs formed when opposite ions come close enough to be separated by a distance < r*
Bjerrum As - Charge of ions increases (zi): r* increases, probability of ion pair formation increases. - Temperature increases, r* decreases, probability of IP formation decreases. Kinetic energy acts against attraction. - Polarity of solvent increases (er), attraction decreases, probability of IP formation decreases
Electrostatic potential energy for interaction between two univalent ions: Substitute r = r* For univalent electrolyte in water at 25 o. C, IP formation is negligible r* is only 0. 358 nm. Very difficult to bring the opposite ions so close!
Ionic Mobilities
Transport Numbers c=1 M c += a M c -= b M
Electroneutrality condition
c=1 M c += a M c -= b M
Let 4 F be passed through the cell; t+=3 t- Before electrolysis On electrolysis After electrolysis
Let 4 F be passed through the cell; t+=3 t- 4 Cl- -4 e- 2 Cl 2 4 H+ +4 e- 2 H 2 3 mol H+ 1 mol Cl-
For anodic region: Cresidual = Cinitial – Creact + C transfer 3 = 6 – 4 + C transfer t- = 1 / 4 = 0. 25 t+ = 3 / 4 = 0. 75
measurement of transport numbers by Hittorf method The method of Hittorf is based on concentration changes in the anodic region and cathodic region in an electrolytic cell, caused by the passage of current through the electrolyte.
Let 1 F be passed through the cell;
A solution of Li. Cl was electrolyzed in a Hittorf cell. After a current of 0. 79 A had been passed for 2 h, the mass of Li. Cl in the anode compartment has decreased by 0. 793 g. a. Calculate the transport numbers of Li+ and Cl-. b. If Lo(Li. Cl) is 115 W-1 cm 2 mol-1, what are the molar ionic conductivities and the ionic mobilities?
2) The moving-boundary method MA, MA’ have an ion in common. The boundary, rather difference in color, refractivity, etc. is sharp. In the steady state, the two ions move with the same velocity.
When Q coulomb passes, the boundary moves x, the cross-sectional area of the tube is A: No. of mole of H+ that passed from AA’ to BB’ n=c. V=c+. A. x Charge carried by these moles: Q+=z+ F n+=z+ F c+ A x
Sample: When A = 1. 05× 10 -5 m 2, c(HCl) = 10. 0 mol m-3, I = 0. 01 A for 200 s, x was measured to be 0. 17 m. Calculate t (H+). Solution: t+ = 0. 17 m× 1. 05 × 10 -5 m 2 × 10. 0 mol m-3 × 1 × 96500 C mol-1 / 0. 01 A × 200 S = 0. 82
Kohlrausch’s Law of Independent migration Valid only at infinite dilution!
Experimentally determined - - -
Grotthuss Mechanism Explains the high conductivity of H+ and OH- in water
Ion Solvation Size But larger size means slower motion, the conductivity should drop? !!!! • Smaller size, • larger interaction with water molecule, • hydrate shell larger on Li+, • moving species larger, • Lower conductivity
Viscosity of the solvent acetone / 0. 316 Methyl alcohol 0. 547 m. Pas K+ 0. 0082 0. 0054 0. 0022 Li+ 0. 0075 0. 0040 0. 0015 Walden’s Rule Ethyl alcohol 1. 200 L. h = constant
- Hittorf
- Ordered pair and unordered pair
- Dof of screw pair
- Different mechanisms of drug absorption
- Physiological factors
- Formation initiale vs formation continue
- In electron transfer involving a metallic atom and an
- Complex ion formation and solubility
- Induced dipole induced dipole interaction
- C6h12 fuerza intermolecular
- Fuerzas dipolo dipolo ejemplos
- Uniones intermoleculares
- Lines and angles
- Are complementary angles adjacent
- How many 4-sided figures are in the diagram?
- Prime path testing
- Matched-pair design
- Edge-pair coverage
- Which pair of ratios forms a proportion?
- Think-pair-share advantages and disadvantages
- Matched pairs design
- Electron pair geometry
- Twisted pair kabel
- Lesson 1-5 angle relationships
- Think pair share cooperative learning
- City pair program
- Name the congruent triangles
- Suppose you and a pair of life preservers
- Relationships of angles
- Ling 200