Analytical Chemistry II: Quantitative Analysis - SS3 Chemistry Past Questions and Answers - page 4

Principles and Applications of Volumetric Analysis using Titration Techniques:

Volumetric analysis, also known as titration, is a quantitative analytical technique used to determine the concentration of a substance (analyte) in a sample by reacting it with a standardised solution (titrant) of known concentration. The principles of titration are based on stoichiometry, where the reactants react in specific mole ratios, allowing for precise determination of the analyte's concentration. Titration is widely used in various industries and research fields due to its accuracy, simplicity, and versatility.

Different Types of Titrations and their Indicators:

1.    Acid-Base Titrations: In acid-base titrations, a strong acid reacts with a strong base or vice versa. The endpoint of the titration is determined using indicators such as phenolphthalein, methyl orange, or bromothymol blue, which change colour at specific pH ranges.

2.    Redox Titrations: Redox titrations involve the transfer of electrons between the analyte and the titrant. Common indicators for redox titrations include potassium dichromate (K₂Cr₂O₇) and potassium permanganate (KMnO₄), which change colour upon completion of the redox reaction.

3.    Complexometric Titrations: Complexometric titrations involve the formation of complex ions between the analyte and the titrant. The most commonly used indicator in complexometric titrations is Eriochrome Black T, which changes colour at a specific pH range.

Examples of Titration Applications:

●     Determination of the concentration of hydrochloric acid (HCl) in a laboratory sample using a standardised sodium hydroxide (NaOH) solution in an acid-base titration with phenolphthalein as the indicator.

●     Estimation of the amount of iron (Fe²⁺) in a sample using a standardised potassium dichromate (K₂Cr₂O₇) solution in a redox titration with diphenylamine-sulfuric acid as the indicator.

●     Quantification of calcium (Ca²⁺) in a water sample using a standardised ethylenediaminetetraacetic acid (EDTA) solution in a complexometric titration with Eriochrome Black T as the indicator.

Factors Affecting Accuracy and Precision of Titration Techniques:

1.    Burette Calibration: Incorrect calibration of the burette used to deliver the titrant can lead to errors in volume measurements, affecting the accuracy of the titration.

2.    Indicator Selection: The choice of indicator is crucial, as an inappropriate indicator may lead to an unclear endpoint, resulting in imprecise results.

3.    Titration Speed: The rate at which the titrant is added can impact the endpoint detection. Rapid addition may cause overshooting of the endpoint, leading to inaccurate results.

4.    Pipetting Errors: Inaccuracies in measuring the volume of the analyte or titrant using pipettes can introduce errors in the titration.

5.    Titration Vessel Contamination: Contamination of the titration vessel can lead to unintended reactions, affecting the accuracy and precision of the titration.

Controlling and Minimising Errors in Titration Experiments:

1.    Burette Calibration: Regular calibration of the burette using a known standard solution ensures accurate volume measurements.

2.    Indicator Selection: Choosing an indicator with a suitable pH range for the specific titration reaction can improve the precision of the endpoint determination.

3.    Titration Speed: Titrating slowly near the expected endpoint helps in achieving a more precise endpoint.

4.    Pipetting Techniques: Using calibrated and high-quality pipettes and employing proper pipetting techniques reduce errors in volume measurements.

5.    Clean Titration Vessels: Thoroughly cleaning the titration vessel between experiments prevents contamination and ensures accurate results.

6.    Multiple Trials: Performing multiple titrations and calculating the average helps to reduce random errors and improve the precision of the results.

In conclusion, titration techniques in volumetric analysis offer reliable and precise methods for determining analyte concentrations. However, factors like burette calibration, indicator selection, titration speed, pipetting errors, and vessel contamination can affect the accuracy and precision of titration experiments. By controlling these factors through proper calibration, indicator choice, careful pipetting, and maintaining clean titration vessels, accurate and reproducible results can be obtained, enhancing the reliability of titration analyses.