10th and 11th lesson (1)

Acid Base Titration Overview

Key Concepts

• Titration: A method to determine the concentration of a solute by reacting it with a titrant of known concentration.

• End Point (E.P): The point in a titration at which the reaction is complete, often indicated by a color change due to an indicator.

Titration of Polyfunctional Bases Against Strong Acids

Example: Na2CO3 Titrated Against HCl

• Titration Curve: Displays two breaks indicating two reactions.

  • First Break: Reaction of Na2CO3 with the first mole of HCl.

  • Second Break: Further reaction with the second mole of HCl.

• Indicators:

  • First Endpoint (E.P1): Use phenolphthalein (Ph.Ph) as indicator for the first proton.

  • Second Endpoint (E.P2): Use methyl orange (M.O) for the second proton.

Calculating pH

• Before Titration:

  • Species present: Na2CO3 (Basic salt)

  • Formula: pH = 1/2 (pKw - pCs + pKa2)

• At 1st Equivalence Point (NaHCO3):

  • pH = 1/2 (pKa1 + pKa2) (Half neutralization)

• For One Conical Method:

  • E.P1 = E.P2 = Na2CO3 + HCl reactions lead to NaHCO3 + NaCl and so on.

• For Two Separate Conical Methods: Similar reactions with different endpoints but same conceptual foundation.

Titration of Mixtures

Example: Mixture of HCl & HAc

• One Aliquot Method:

  • E.P1 by M.O = HCl

  • E.P2 by Ph.Ph = HAc

• Two Aliquots Method:

  • E.P1 by M.O = HCl

  • E.P2 by Ph.Ph = HCl + HAc

Example: Mixture of H3PO4 & HAc

• Both methods yield similar endpoints for first and second protons of H3PO4 and HAc.

Titration of Boric Acid (H3BO3)

• Characteristics: Very weak acid, low dissociation constant (Ka), almost non-ionized.

• Enhancing Ionization: Add Glycerol or polyhydroxy compounds that react to create stronger acids to titrate.

Determination of Borax (Na2B4O7)

• Undergoes hydrolysis leading to formation of boric acid and NaOH.

• Use two-step conical method:

  • First, liberate NaOH from borax by titration with HCl.

  • Second, add glycerol, liberate protons from boric acid and titrate with NaOH.

Biphasic Titration

• Used for organic aromatic acid salts (e.g. Na salicylate).

• Titration occurs in a separating funnel to avoid turbidity; ether is added to extract the formed acid.

Kjeldahl's Method

• For nitrogenous organic compounds (e.g. proteins).

• Process includes digestion, distillation, and back titration to determine nitrogen content.

Formol Titration

• Indirect method for amino acids and ammonium salts.

• Formaldehyde is added to modify the structure of the amino acid for titration.

Determination of Insoluble Oxides and Carbonates

• Method: Back titration with standard NaOH to assess the amount of insoluble oxides or carbonates in solution.

Titration of Weakly Acids and Bases in Nonaqueous Solvents

• Solvents Utilized: Aprotic solvents (e.g. chloroform), protophilic, protogenic, and amphiprotic solvents.

• Applications: Useful for weakly acidic/basic compounds that cannot be titrated in aqueous solutions.

Summary

• Acid-base titrations encompass various methods and scenarios, including mixtures and the behavior of specific weak acids/bases. Importance lies in mastering calculations, endpoint recognition, and method application for accurate analytical chemistry.

Practical Applications

• Applications of the Methods:

  • Titration of industrial products.

  • Environmental monitoring of acid/base levels.

  • Pharmaceutical compound analysis.