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• Acid-Base Titration


  A technique to determine the concentration of an acid or base analytes by neutralizing the unknown concentration of an acidic or basic analyte with the known concentration of an acid or base
• Neutralization Reaction


  Also known as Acid-Base Titration
• Acid-Base Titration


  • Uses an indicator where the indicator will change its color at the end point of the titration
  • Allows the quantitative analysis for the unknown acid/alkali concentration

  
• Arrhenius definition of acids

  Substances that increase hydrogen (H+) ions when added to water; form hydronium ions (H3O+) when combined in water

  
• Arrhenius definition of bases

  Substances that produce hydroxide ions (OH-) when in water

  
• Bronsted-Lowry definition of acids

  Proton (hydrogen ion) donor
• Bronsted-Lowry definition of bases

  Proton (hydrogen ion) acceptor
• Strong acid


  Dissociates (or ionizes) completely in aqueous solution to form more hydronium ions (H3O)
• Weak acid


  Does not dissociate completely in aqueous solution
• Strong base


  Dissociates completely in aqueous solution to form hydroxide ions (OH-)
• Weak base


  Does not dissociate completely in aqueous solution to form hydroxide ions (OH-)
• Acid-Base (Neutralization) Titration


  1. Analyte solution

  2. Titrant added

  3. Indicator changes color at end point

  4. Quantitative analysis of unknown acid/alkali concentration

  
• Equivalence point


  Point in titration at which the amount of titrant added is just enough to completely neutralize the analyte solution. At the equivalence point, moles of base = moles of acid and the solution only contains salt and water.

  
• Acid-Base Indicators


  • Weak organic acids or bases in which the undissociated molecule has one color, and the anion and cation produced by dissociation has another color
  • Used to determine the end-point in neutralization process
  • Used to determine H+ concentration or pH
  • Used to indicate that a desired change in pH has happened

  
• Titration curve


  • A graph of the pH versus the amount of the reagent progressively added to the original sample
  • Can be used to determine the equivalence point of an acid-base reaction
  • Can be used to determine the pH of the solution at equivalence point, which is dependent on the strength of the acid and strength of the base used in the titration

  
• Types of neutralization titration curves

  • Titration of a strong acid with strong base
  • Titration of a weak acid with a strong base
  • Titration of a strong acid with a weak base
  • Titration of a weak base with a weak acid
• Titration of a strong acid with a strong base


  • pH = 7 at equivalence point
• Titration of a weak acid with a strong base


  • pH > 7 at equivalence point
• Titration of a strong acid with a weak base


  • pH < 7 at equivalence point
• Rules for the use of indicators:
• Standardization


  The process of determining the exact concentration (normality or molarity) of a solution. Titration is one type of analytical procedure often used in standardization.

  
• Commonly used standard solutions

  • Acids: Hydrochloric Acid, Sulfuric Acid
  • Alkalis: Sodium Hydroxide, Potassium Hydroxide, Barium Hydroxide

  
• Acidimetric Analysis


  The direct and residual titrimetric analysis of bases using an accurately measured volume of acid

  
• Alkalimetric Analysis


  Analyzing the concentration of acids using a known concentration of alkaline solution
• Direct Titration


  1. Burette is filled with titrant solution

  2. Indicator is added to the solution to be titrated

  3. Titrant is added to flask with swirling until the end point

  4. Read and record the volume of titrant delivered

  
• Residual Titration (Back Titration)

  1. Analyte is combined with excess standard solution

  2. Burette is filled with second titrant

  3. Indicator is added to the solution to be titrated

  4. Second titrant is added to flask with swirling until the end point

  5. Read and record the volume of titrant delivered

  
• Direct Titration formula


  % Purity = (N x ml x mEq) / (Weight of Sample x 100)

  mEq = (MW / f x 1000)

  
• Residual Titration formula


  % Purity = (N x mla - N x mlb) x mEq / Weight of Sample x 100

  
• Acidimetric Analysis: Direct Titration

  • Sample/Analyte
  • Titrant: 1 N Sulfuric Acid
  • Indicator: Methyl orange
  • Assay of Sodium Bicarbonate

  
• Possible reasons for not obtaining stoichiometric points: The sample is insoluble, the rate of its reaction with the standard acid is relatively slow, or when the analyte to be assayed does not give a distinct sharp end point with an indicator by direct titration

  
• CARITAS• VERITAS•UNITAS•PHARMACY PROGRAM
• Acidimetric Analysis


  1. Analyte is combined with excess standard solution

  2. Burette is filled with second titrant

  3. Indicator is added to the solution to be titrated

  4. Second titrant is added to flask with swirling until the end point

  5. Read and record the volume of titrant delivered

  
• Direct Titration


  % Purity = (N x ml x mEq) / (Weight of Sample x 100)

  
• mEq


  (MW / f x 1000)
• Residual Titration


  % Purity = (N x mla - N x mlb) x mEq / Weight of Sample x 100

  
• Direct Titration


  • Assay of Sodium Bicarbonate
  • Assay of Sodium Hydroxide
  • Assay of Sodium Salicylate Tablets

  
• Sample Problem


  A 3-gram sample of sodium bicarbonate (NaHCO3) required 35.1 ml of 1 N sulfuric acid in titration to a methyl orange end point. What is the % purity (w/w) of the analyte?

  
• % Purity = (N x ml x mEq) / (weight of sample x 100) = (1 N x 35.1 ml x (84 g/mol / 1 x 1000)) / 3 grams x 100 = 98.28%
• Checkpoint


  If a 0.2800-g sample of Sodium Bicarbonate (96.5% NaHCO3) is titrated with 0.9165 N sulfuric acid, what volume of the acid should be required to produce an end point?

  
• % Purity = (N x ml x mEq) / (weight of sample x 100) = 96.5% x 0.2800 / (0.9165)(0.084) = 3.51 ml