Chapter 10 - CHAPTER 10 EFFECT OF ELECTROLYTES ON CHEMICAL...

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CHAPTER 10 EFFECT OF ELECTROLYTES ON CHEMICAL EQUILIBRIA The position of most solution equilibria depends on the electrolyte concentration of the medium, even when the added electrolyte contains no ion in common with those involved in the equilibrium. H 3 AsO 4 + 3I - + 2H + H 3 AsO 3 + I 3 - + H 2 O If an electrolyte, such as barium nitrate, potassium sulfate, or sodium perchlorate, is added to this solution, the color of the triiodide ion becomes less intense. This decrease in color intensity indicates that the concentration of I 3 - has decreased and that the equilibrium has been shifted to the left by the added electrolyte.
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How Do Ionic Charges Affect Equilibria? The magnitude of the electrolyte effect is highly dependent on the charges of the participants in an equilibrium. When only neutral species are involved, the position of equilibrium is essentially independent of electrolyte concentration. With ionic participants, the magnitude of the electrolyte effect increases with charge. In a 0.02 M solution of potassium nitrate, the solubility of barium sulfate is larger than it is in pure water by a factor of 2. The solubility of barium iodate by a factor of only 1.25 and that of silver chloride by 1.2
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What Is the Effect of Ionic Strength on Equilibria? The effect of added electrolyte on equilibria is independent of the chemical nature of the electrolyte but depends on a property of the solution called the ionic strength . This quantity is defined as ionic strength = μ =1/2([A]Z A 2 + [B]Z B 2 + [C]Z C 2 + …) Where [A], [B], [C], represent the molar species concentrations of ions A, B, C, … and Z A , Z B , Z C , … are their ionic charges. For solutions with ionic strengths of 0.1 M or less, the
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Chapter 10 - CHAPTER 10 EFFECT OF ELECTROLYTES ON CHEMICAL...

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