Jas Ion Transport in Solution Part1

8/10/2019 Jas Ion Transport in Solution Part1

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TRANSPORT OF IONS IN SOLUTION

Jaslin Ikhsan, Ph.D.Chemistry Ed. Department

State University of Yogyakarta

Conductivity of electrolyte solutionsStrong and weak electrolyte


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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


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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 areaA, itfollows:

GR

in units of 1 1,

G A

L

Where,

:the conductivity,

L :the distance separating the plates

Units:

GS (siemens)

R

S m-1


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Conductivity of Electrolyte Solution

The conductivity of a solution depends on the number of ions

present. Consequently, the molar conductivitymis used

C is molar concentration of electrolyte and

unit of mis S m2mol-1

mC

In real solutions,mdepends on the concentration

of the electrolyte. This could be due to:

Ion-ion interactions1

The concentration dependence of conductance

indicates 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


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Strong Electrolyte

Fully ionized in solution

Kohlrauschs law

0m is the limiting molar conductivity

K is a constant which typically depends on the

stoichiometry of the electrolyte

C1/2arises from ion-ion interactions as estimated by the

Debye-Hckel theory.

m m KC 0 1 2/


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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

0m


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Weak Electrolyte

Not fully ionized in solution

HA aq H O l H O aq A aq

c c c

( ) ( ) ( ) ( )

( )

2 3

1

K c

a

2

1

,

2

2

2

2

0

4

2

2

4

2

c K K

c K K

K K K c

c

K

c

K K c

c

a a

a a

a a a

a a a

K

c

K

c

c

K

K

c

c

K

a a

a

a

a

2 21

4

21

41

1 2

1 2

/

/

11

c

Ka is degree of ionisation


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Weak Electrolyte

The molar Conductivity (at

higher concentrations) can

be expressed as:

At infinite dilution, theweak acid is fully

dissociated (= 100%)

It can be proven by the

Ostwald dilution law whichallows estimating limiting

molar conductance:

m m 0

m m

m m

m m

m m a

m m a m

m

m

x

x c

K

c

Kx

0

0

0

0

0 0 0

1 1

1 1 1

1 11

1 1

1 10 0 2

m m

m

a m

c

K

( )


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Weak Electrolyte

The limiting molar conductance:

1 10 0 2

m m

m

a m

c

K

( )

Graph to determine the limitingvalue of the molar conductivity of

a solution by extrapolation to zero

concentration

Hukum Pengenceran

Ostwald


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Diskusi:

1. Konduktivitas molar larutan elektrolit pada 250C adalah 135,5 S

cm2 mol-1dan konsentrasinya adalah 5,35 x 10-2M. 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 250C konduktivitas larutan elektrolit kuat dalam air adalah109,9 S cm2 mol-1untuk konsentrasi 6,2 x 10-3M dan 106,1 S

cm2 mol-1untuk konsentrasi 1,50 x 10-2M. Berapakah

konduktivitas molar pembatas elektrolit tersebut? (30)

4. 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)


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Thank You

Jas Ion Transport in Solution Part1

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