TRANSPORT OF IONS IN SOLUTION

Presentasi berjudul: "TRANSPORT OF IONS IN SOLUTION"— Transcript presentasi:

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 as the 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, the molar conductivity Λm is 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 the electrolyte. This could be due to: Ion-ion interactions  γ  1 The concentration dependence of conductance indicates that there are 2 classes of electrolyte Strong electrolyte: molar conductivity depends slightly 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 the electrolyte. 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 conductivity can 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 molar conductivity of a solution by extrapolation to zero concentration

11 Diskusi: Konduktivitas molar larutan elektrolit pada 250C adalah 135,5 S cm2 mol-1 dan konsentrasinya adalah 5,35 x 10-2 M. Hitunglah konduktivitas larutan! (20) Sel konduktivitas mempunyai elektrode bidang yang sejajar, masing-masing luasnya 2,2 cm x 2,2 cm, dan terpisah sejauh 2,75 cm. Jika sel diisi dengan larutan elektrolit, tahanannya adalah 351 ohm. Berapakah konduktivitas larutan? (25) Pada 250C konduktivitas larutan elektrolit kuat dalam air adalah 109,9 S cm2 mol-1 untuk konsentrasi 6,2 x 10-3 M dan 106,1 S cm2 mol-1 untuk konsentrasi 1,50 x 10-2 M. Berapakah konduktivitas molar pembatas elektrolit tersebut? (30) Konduktivitas molar 0,1000 M KCl (aq) adalah 129 S cm2 mol-1 dan tahanan terukur dalam sel konduktivitas adalah 28,44 ohm. Tahanan itu besarnya 28,50 ohm jika sel yang sama berisi 0,1000 M NH4Cl (aq). Hitunglah konduktivitas molar NH4Cl (aq) pada konsentrasi ini! (25)

12 Thank You