1_Electrolytes_in_solution_part_1

1_Electrolytes_in_so - Electrolytes C300 FALL 2011 What is an Electrolyte An electrolyte is a substance containing free ions that behaves as an

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Electrolytes C300 FALL 2011
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What is an Electrolyte? • An electrolyte is a substance containing free ions that behaves as an electrically conductive medium Conductivity and Conductance V=IR (Ohm’s Law) R = ρ ( /A), ρ – specific resistance or resistivity C = κ (A/ ), κ specific conductance (conductivity) where κ =1/ ρ Conductivity: ability to conduct an electric current between 2 points Conductance (C): how easily electricity flows along a certain path in electric element Molar conductivity Λ m = κ /c (units S m 2 mol -1 ) (c – molar concentration)
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Λ m = Λ m o K c Λ o – equivalent conductance at infinite dilution or limiting molar conductivity (ions no longer interact with each other) K - positive constant for given electrolyte Molar Conductivity • At low concentrations the molar conductivity of strong electrolytes vary linearly with the square root of the concentration limiting molar conductivity : Λ o m = λ + + λ - λ + & λ - ionic conductivities of the individual cations and ions Strong electrolyte : Λ m depends slightly on the molar concentration Weak electrolyte : Λ m falls sharply to low values as the concentration increases.
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The degree of dissociation can be determined from molar conductivity • At any given concentration an electrolyte is typically partially dissociated • At infinite dilution it is completely dissociated. α is the degree of dissociation α = Λ m Λ m o
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HA H + + A - (weak acid) K a = c Λ m 2 Λ m o Λ m o − Λ m ( ) 1 Λ m = 1 K a Λ m o ( ) 2 Λ m c ( ) + 1 Λ m o K a values can be determined from Λ m •Ostwald dilution law •What plot could you make to obtain an acidity constant?
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Ionic conductivities depends on the ease of ionic movement, so does molar conductivity ( Λ m ) Ionic mobility (u +
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This note was uploaded on 12/04/2011 for the course CHEM 300 taught by Professor N.gerber during the Fall '11 term at S.F. State.

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1_Electrolytes_in_so - Electrolytes C300 FALL 2011 What is an Electrolyte An electrolyte is a substance containing free ions that behaves as an

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