TRANSPORT OF IONS IN SOLUTION

1. TRANSPORT OF IONS IN SOLUTION • Conductivity of electrolyte solutions • Strong and weak electrolyte Jaslin Ikhsan, Ph.D. Chemistry Ed. Department State University of Yogyakarta

2. Mahasiswa dapat menjelaskan pengertian konduktansi dan konduktivitas • Mahasiswa dapat menghitung konduktivitas molar larutan • Mahasiswa dapat menjelaskan hukum pengenceran Ostwald • Mahasiswa dapat menentukan pKa dengan menggunakan hasil pengukuran konduktivitas

3. Conductivity of Electrolyte Solution • Ions in solution can be set in motion by applying a potential difference between two electrodes. • The conductance (G) of a solution is defined asthe inverse of the resistance (R): • For parallel plate electrodes with area A, it • follows: Where, Κ: the conductivity, L : the distance separating the plates Units: G → S (siemens) R → Ω κ → S m-1

4. Conductivity of Electrolyte Solution • The conductivity of a solution depends on the number of ions present. Consequently, themolar conductivity Λmis used • C is molar concentration of electrolyte and unit of Λm is S m2 mol-1 • In real solutions, Λm depends on the concentration of theelectrolyte.This could be due to: • Ion-ion interactions  γ  1 • The concentration dependence of conductanceindicates that there are 2 classes of electrolyte • Strong electrolyte: molar conductivity dependsslightly on the molar concentration • Weak electrolyte: molar concentration falls sharply as the concentration increases

5. Conductivity of Electrolyte Solution • In real solutions, Λm depends on the concentration of theelectrolyte. This could be due to: • Ion-ion interactions  γ  1 • Incomplete dissociation • of electrolyte strong electrolyte, weak dependence of Λm on C weak electrolyte, strong dependence of Λm on C

6. Strong Electrolyte • Fully ionized in solution • Kohlrausch’s law • Λ0m is the limiting molar conductivity • K is a constant which typically depends on the stoichiometry of the electrolyte • C1/2 arises from ion-ion interactions as estimated by the Debye-Hückel theory.

7. Strong Electrolyte • Law of the independent migration of ions: limiting molar conductivitycan be expressed as a sum of ions contribution • ions migrate independently in the zero concentration limit

8. Weak Electrolyte • Not fully ionized in solution

9. Weak Electrolyte • The molar Conductivity (at higher concentrations) can be expressed as: • At infinite dilution, the weak acid is fully dissociated (α = 100%) • It can be proven by the Ostwald dilution law which allows estimating limiting molar conductance:

10. Weak Electrolyte • The limiting molar conductance: Hukum Pengenceran Ostwald Graph to determine the limiting value of the molarconductivity of a solution by extrapolation to zero concentration

11. Diskusi: Konduktivitas molar larutanelektrolitpada 250C adalah 135,5 S cm2 mol-1dankonsentrasinyaadalah 5,35 x 10-2 M. Hitunglahkonduktivitaslarutan! (20) Selkonduktivitasmempunyaielektrodebidang yang sejajar, masing-masingluasnya 2,2 cm x 2,2 cm, danterpisahsejauh 2,75 cm. Jikaseldiisidenganlarutanelektrolit, tahanannyaadalah 351 ohm. Berapakahkonduktivitaslarutan? (25) Pada 250C konduktivitaslarutanelektrolitkuatdalam air adalah 109,9 S cm2 mol-1untukkonsentrasi 6,2 x 10-3 M dan 106,1 S cm2 mol-1untukkonsentrasi 1,50 x 10-2 M. Berapakahkonduktivitas molar pembataselektrolittersebut? (30) Konduktivitas molar 0,1000 M KCl (aq) adalah 129 S cm2 mol-1dantahananterukurdalamselkonduktivitasadalah 28,44 ohm. Tahananitubesarnya 28,50 ohm jikasel yang samaberisi 0,1000 M NH4Cl (aq). Hitunglahkonduktivitas molar NH4Cl (aq) padakonsentrasiini! (25)

12. Thank You