Chapter 14 - Chapter 14 Principles of Neutralization...

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Chapter 14 Principles of Neutralization Titrations Like any titration, neutralization titrations depend on a chemical reaction between the analyte and a standard reagent. The point of chemical equivalence is indicated by a chemical indicator or an instrumental measurement. The discussion here focuses on the types of standard solutions and the chemical indicators that are used for neutralization titrations.
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Standard Solutions The standard solutions employed in neutralization titrations are strong acids or strong bases because these substances react more completely with an analyte than their weaker counterparts do and thus yield sharper end points. Standard solutions of acids are prepared by diluting concentrated hydrochloric, perchloric, or sulfuric acid. Standard solutions of bases are ordinarily prepared from solid sodium or potassium and occasionally barium hydroxides. The concentrations of these bases must be established by standardization.
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Acid/Base Indicators Many substances display colors that depend on the pH of the solutions in which they are dissolved. An acid/base indicator is a weak organic acid or a weak organic base whose undissociated form differs in color from its conjugate form. e.g., the behavior of an acid-type indicator, HIn, is described by the equilibrium HIn + H 2 O In - + H 3 O + acid color base color The equilibrium for a base-type indicator, In, is In + H 2 O InH + + OH - base color acid color
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…continued… The equilibrium-constant expression for the dissociation of an acid-type indicator takes the form Rearranging leads to The hydronium ion concentration determines the ratio of the acid to the conjugate base form of the indicator
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Chapter 14 - Chapter 14 Principles of Neutralization...

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