4. VOLUMETRIC ANALYSIS

What is Volumetric Analysis?

Volumetric analysis is a laboratory method used to calculate how much of a chemical is present in a solution. It works by measuring the volume of a solution with a known concentration (called the standard solution) required to react completely with another solution containing an unknown amount of substance. This process is popularly called titration and is widely used in chemistry and pharmaceutical laboratories.

It is also known as titrimetric analysis. Common glassware used in volumetric analysis includes burettes, pipettes, volumetric flasks, conical flasks, and measuring cylinders. A conical flask is often used during titration because it prevents loss of solution while mixing.

ACTUAL NOTES:

Fundamentals of Volumetric Analysis:

The basic idea behind volumetric analysis is simple:

• The solution to be tested contains an unknown amount of a chemical.
• A standard solution reacts with it in the presence of an indicator that shows the end point by a colour change.
• The reaction stops when both solutions have combined completely.
• By using the concentration and volume of the standard solution, the unknown amount can be calculated.
• The chemical equation helps determine how much of the unknown substance was present.

Procedure of Volumetric Analysis:

• A known volume of analyte is taken in a flask and indicator is added.
• The titrant is filled into a burette and slowly added to the flask until the indicator changes colour.
• The exact volume of titrant used at the endpoint is recorded.
• Accurate weighing, proper glassware, and careful dropwise addition are essential to avoid errors.
• The concentration is calculated using known formulas based on volume and molarity.

Types of Volumetric Analysis:

Volumetric analysis mainly includes five types of titrations:

1. Acid–Base Titration: Based on neutralisation (acid reacts with base). Common indicator: Phenolphthalein.
2. Non-Aqueous Titration: Used for weak or water-insoluble drugs using non-water solvents.
3. Precipitation Titration: Produces a solid precipitate; e.g., AgNO3 with chloride salts.
4. Complexometric Titration: Measures metal ions using chelating agents such as EDTA.
5. Redox Titration: Based on oxidation–reduction reactions using oxidising and reducing agents.

Acid–Base Titration:

This method finds the unknown concentration of acids or bases using the reaction:
Acid + Base → Salt + Water
Indicators like phenolphthalein signal the endpoint when equal amounts of H⁺ and OH^– are present. Theories explaining acids and bases include Arrhenius, Bronsted–Lowry, and Lewis theories.

Non-Aqueous Titration:

Used when drugs are weak or do not dissolve in water. Special organic solvents like glacial acetic acid are used to get sharp colour changes. Indicators used include crystal violet, methyl red, thymol blue, and quinaldine red.

Precipitation Titration:

In this method, a solid (precipitate) forms during the reaction. Silver nitrate is commonly used for chloride estimation. Endpoints can be detected using Mohr’s method, Volhard’s method, or Fajan’s method.

Complexometric Titration:

This titration is used for metal ions like Ca, Mg, Pb, and Zn. It relies on formation of stable metal complexes. The most common reagent is EDTA. Indicators for metal ions include Eriochrome Black T, Murexide, and Xylenol Orange.

Redox Titration:

Redox titration uses oxidation (loss of electrons) and reduction (gain of electrons). Permanganate and iodine solutions act as their own indicators. Redox titrations are used to estimate drugs like aspirin, vitamin C, and antibiotics.