Volumetric Analysis: Principles, Techniques, and Applications

Volumetric Analysis

Requirements for Volumetric Reactions

For a reaction to be used in volumetric analysis, it must meet the following criteria:

• The reaction between the titrant and the titrated substance must be quantitative, without adding excess reagent. The reaction must be complete at the equivalence point.
• The reaction must be fast. If it is slow, it is possible to accelerate it with temperature or catalysts.
• The reaction must be stoichiometric and definite.
• To determine the endpoint, a sensitive method must be available.

Characteristics of a Standard Solution

To prepare a standard solution, there are two methods:

1. Directly dissolve a standard substance and dilute to an exact volume (using a volumetric flask).
2. Prepare a solution of approximate concentration and standardize it with a primary standard substance.

Primary Standard Requirements

A primary standard must meet the following requirements:

• Be a pure elementary chemical species.
• Have a well-known formula.
• Must not be altered by air or by drying.
• Must be easily soluble in the conditions under which it will be prepared.
• Must react instantly and stoichiometrically under the conditions of the titration.
• Whether it is an acid or base, oxidizing or reducing agent, it should be strong.
• It is desirable that the molecular weight or equivalent weight be as large as possible, so that errors are less significant.

Changes in Concentration During Titration

During the titration, there must be an abrupt change in some property of the reaction mixture at the equivalence point. The property that changes depends on the type of volumetric reaction:

• Acid-Base Titration: When titrating an acid with a base or a base with an acid, the abrupt change is due to a slight excess of one reactant that produces a sudden change in pH.
• Redox Titration: When titrating an oxidant with a reductant or vice versa, the abrupt change is due to a slight excess of one reactant leading to an abrupt change in the cell potential formed by two electrodes.
• Precipitation Titration: When titrating an ionic substance with a precipitating reagent, the abrupt change is due to an excess of the precipitating reagent that produces a sharp decrease in the concentration of the precipitated ion.

Acid and Base Concepts

Arrhenius Theory

• Acid: Any substance that releases H⁺ ions (e.g., H₃O⁺, HCl).
• Base: Any substance that releases OH^- ions (e.g., NaOH).

Bronsted-Lowry Theory

• Acid: Any substance that can donate protons (e.g., NH₄⁺).
• Base: Any substance that can accept protons (e.g., NH₃).

Lewis Theory

• Acid: Any substance that can accept an electron pair.
• Base: Any substance that can donate an electron pair.