Acid-base titration

Acid-base titration

Acid-base titration is a laboratory method used in chemistry to determine the concentration of an unknown acid or base solution by reacting it with a base or acid of known concentration. This process involves the gradual addition of the acid or base of known concentration, referred to as the titrant, to the solution of unknown concentration, known as the analyte, until the reaction reaches its end point. The end point is typically indicated by a color change of an indicator or by reaching a specific pH value that can be measured using a pH meter.

Principles

The underlying principle of acid-base titration is based on the neutralization reaction that occurs between acids and bases. This reaction can be represented by the general equation:

\[ \text{HA} + \text{BOH} \rightarrow \text{BA} + \text{H}_2\text{O} \]

where HA represents the acid, BOH represents the base, BA is the salt formed, and H2O is water. The point at which the amount of titrant added is stoichiometrically equivalent to the concentration of the analyte in the solution is known as the equivalence point. The equivalence point is the ideal completion of the neutralization reaction, although the observed end point may slightly differ depending on the indicator used.

Procedure

The procedure for an acid-base titration involves several steps: 1. Preparation of the solutions: The solution of unknown concentration is placed in a flask, and a few drops of an appropriate indicator are added. The titrant is placed in a burette. 2. Titration: The titrant is gradually added to the analyte solution while continuously mixing until the end point is reached, indicated by a color change of the indicator. 3. Calculation: The concentration of the unknown solution can then be calculated using the formula:

\[ C_aV_a = C_bV_b \]

where \(C_a\) is the concentration of the acid, \(V_a\) is the volume of the acid, \(C_b\) is the concentration of the base, and \(V_b\) is the volume of the base used.

Indicators

Indicators are substances that change color at a particular pH level and are crucial for determining the end point of a titration. Common indicators include phenolphthalein, which changes from colorless to pink at a pH of about 8.2, and methyl orange, which changes from red to yellow at a pH of about 3.7. The choice of indicator depends on the strength of the acid and base involved in the reaction and the specific pH range over which the color change occurs.

Applications

Acid-base titration is widely used in various fields such as:

• Analytical chemistry for determining the concentrations of solutions.
• Pharmaceutical industry for quality control and validation of drug formulations.
• Environmental science for analyzing the acidity or alkalinity of water bodies.
• Food industry for determining the acidity of food products.

See also

• Titration
• pH
• Indicator (chemistry)
• Neutralization (chemistry)