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Acid-Base Titrations A. Definition: volumetric analysis of the concentration of an unknown 1. Titrant = solution of known concentration whose volume is measured 2. Analyte = solution whose concentration is to be determined
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Acid-Base Titrations A. Definition: volumetric analysis of the concentration of an unknown 1. Titrant = solution of known concentration whose volume is measured 2. Analyte = solution whose concentration is to be determined 3. Equivalence Point = amount of titrant just reacts with all analyte • Indicator = changes color at endpoint of the titration • Neutralization Reactions • Water is a nonelectrolyte (not highly ionized in solution) • H+(aq) + OH-(aq) -------> H2O(l) • Reaction of an acid and a base (usually to form water) = Neutralization • H+ is a strong acid and will completely react with any weak base present H+(aq) + NH3(aq) -------> NH4+(aq) • OH- is a strong base and will completely react with any weak acid present OH-(aq) + HC2H3O2(aq) -------> H2O(l) + C2H3O2-(aq) • Similar to a precipitation reaction, except the product is a liquid (H2O)
C. Acid-Base Titration results in neutralization of all of the analyte • 1. H+(aq) + OH-(aq) -------> H2O(l) • 2. Phenolphthalein indicator is colorless in acid and pink in base • 3. A buret accurately measures the amount of titrant added The flask contains acid of unknown concentration and phenolphthalein. The buret contains base of a known concentration Base is added dropwise. The faint pink color goes away as you stir. The endpoint hasn’t been reached yet. The endpoint has now been reached as the pink color persists. Measuring the volume of base dispensed aids calculation.
4. Standardizing the base solution: 1.3009g KHP is dissolved in distilled water (doesn’t matter how much) and titrated with 41.20ml unknown NaOH solution. • HP-(aq) + OH-(aq) -------> H2O(l) + P2-(aq) • 5. Calculating the concentration of the analyte: • 25.00 ml of an unknown aqueous sample of HCl was titrated with 10.59ml of 0.1546M NaOH. • HCl(aq) + NaOH(aq) -------> H2O(l) + Cl-(aq) + Na+(aq)