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

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Presentasi berjudul: "TRANSPORT OF IONS IN SOLUTION Jaslin Ikhsan, Ph.D. Chemistry Ed. Department State University of Yogyakarta  Conductivity of electrolyte solutions  Strong."— Transcript presentasi:

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

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 Λ m is used C is molar concentration of electrolyte and unit of Λ m is S m 2 mol -1 In real solutions, Λ m 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, Λ m depends on the concentration of the electrolyte. This could be due to: 1.Ion-ion interactions  γ   1 2.Incomplete dissociation of electrolyte strong electrolyte, weak dependence of Λ m on C weak electrolyte, strong dependence of Λ m on C

6 Strong Electrolyte  Fully ionized in solution  Kohlrausch’s law Λ 0 m is the limiting molar conductivity K is a constant which typically depends on the stoichiometry of the electrolyte  C 1/2 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: Graph to determine the limiting value of the molar conductivity of a solution by extrapolation to zero concentration Hukum Pengenceran Ostwald

11 Diskusi: 1.Konduktivitas molar larutan elektrolit pada 25 0 C adalah 135,5 S cm 2 mol -1 dan konsentrasinya adalah 5,35 x M. Hitunglah konduktivitas larutan! (20) 2.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) 3.Pada 25 0 C konduktivitas larutan elektrolit kuat dalam air adalah 109,9 S cm 2 mol -1 untuk konsentrasi 6,2 x M dan 106,1 S cm 2 mol -1 untuk konsentrasi 1,50 x M. Berapakah konduktivitas molar pembatas elektrolit tersebut? (30) 4.Konduktivitas molar 0,1000 M KCl (aq) adalah 129 S cm 2 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 NH 4 Cl (aq). Hitunglah konduktivitas molar NH 4 Cl (aq) pada konsentrasi ini! (25)

12 Thank You


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