Question

a. What is meant by the end point of a titration? b. What is the role of an indicator in the titration process? c. On what basis is an indicator selected for a particular titration experiment?

Short answer

The end point of a titration marks the completion of the reaction. The indicator shows when the end point is reached via a color change. Indicators are selected based on the expected pH at the equivalence point.

Step-by-step solution

Understanding the End Point of Titration

The end point of a titration is the point at which the reaction between the titrant (the solution of known concentration) and the analyte (the solution of unknown concentration) is complete. This is typically indicated by a color change, a precipitate, or another observable physical change.

Role of an Indicator in Titration

An indicator is a substance that changes color at (or very close to) the equivalence point of the titration. It helps to visually identify the end point of the titration so that the experimenter knows when the reaction is complete.

Selection Criteria for Indicators

Indicators are chosen based on the type of titration and the pH at which the reaction reaches its equivalence point. For acid-base titrations, the indicator should have a color change at a pH close to the pH of the equivalence point of the particular titration. For example, phenolphthalein is commonly used for titrations with a relatively large pH change at the equivalence point.

Key concepts

titration process

Titration is a common laboratory method used to determine the concentration of an unknown solution. The process involves adding a titrant (a solution of known concentration) to the analyte (the solution of unknown concentration) until the reaction reaches the end point. The volume of titrant used is then measured to calculate the concentration of the analyte. The titration process can be broken into a few key steps.
First, the titrant is prepared, and its concentration is accurately known. Next, a known volume of the analyte is placed in a flask, and a few drops of indicator are added. The titrant is then slowly added to the analyte from a burette while continuously stirring the mixture.
The titration continues until the indicator shows that the reaction is complete, which is observed at the end point. This is often indicated by a color change, making it easy to recognize when to stop adding titrant.

Finally, the volume of titrant added is recorded, and using stoichiometry, the concentration of the analyte is calculated.

role of indicators

Indicators are vital in the titration process because they help identify when the reaction between the titrant and the analyte is complete. They function by changing color at or near the equivalence point, signaling the end point of the titration. Without indicators, it would be challenging to know when to stop adding the titrant.

Indicators can work in different ways, such as:

• Color change: Many indicators change color at the endpoint, providing a clear visual cue. For example, phenolphthalein turns pink in basic solutions but is colorless in acidic solutions.
• Formation of a precipitate: Some titrations might use an indicator that forms a solid precipitate, clearly signaling the end of the reaction.
• pH change: Some indicators are sensitive to the pH change in the titration mixture, which can be useful in acid-base titrations.

It is crucial to select the correct indicator for a specific titration to ensure accurate results.

selection of indicators

Selecting the right indicator for a titration experiment is essential for accuracy. The choice depends on the type of titration and the pH at which the reaction reaches its equivalence point. Here are some considerations:

• Type of Titration: Different titrations require different indicators. Acid-base titrations need indicators that change color at a particular pH, whereas redox titrations might require indicators that change color at a specific oxidation state.


• pH of Equivalence Point: The chosen indicator should change color at a pH close to the equivalence point of the titration. For example, phenolphthalein is suitable for strong acid-strong base titrations as it changes color around pH 8-9.


• Endpoint Visibility: The color change of the indicator should be distinct and easily noticeable. Indicators that produce a clear color change are preferred to avoid misinterpretation.

By considering these factors, experimenters can ensure that they choose the most appropriate indicator for their titration, allowing for accurate detection of the end point.