Analytical Chemistry II: Quantitative Analysis - SS3 Chemistry Past Questions and Answers - page 5
Compare and contrast acid-base, redox, and complexometric titrations. Explain the principles behind each titration technique, the types of reactions involved, and the respective indicators used for endpoint detection.
Acid-Base, Redox, and Complexometric Titrations:
1. Acid-Base Titrations:
● Principle: Acid-base titrations involve the reaction between an acid and a base to determine the concentration of either the acid or the base in a solution. The principle is based on the neutralisation reaction, where the moles of acid are equivalent to the moles of the base at the endpoint.
● Reactions: In an acid-base titration, a strong acid reacts with a strong base or vice versa to form water and salt. The balanced chemical equation is HX + BOH → H₂O + BX, where X is an anion and B is a cation.
● Indicators: Acid-base indicators, such as phenolphthalein, methyl orange, and bromothymol blue, are used to signal the endpoint of the titration. The indicator changes colour at a specific pH range, corresponding to the neutralisation point.
2. Redox Titrations:
● Principle: Redox titrations involve the transfer of electrons between the analyte and the titrant. The principle is based on the stoichiometric ratio of the reactants and products in the redox reaction.
● Reactions: Redox titrations can involve various redox reactions, such as the oxidation of a reducing agent by a standard oxidising agent or the reduction of an oxidising agent by a standard reducing agent.
● Indicators: Redox indicators are used to detect the endpoint in redox titrations. Potassium dichromate (K₂Cr₂O₇) and potassium permanganate (KMnO₄) are common indicators that change colour upon completion of the redox reaction.
3. Complexometric Titrations:
● Principle: Complexometric titrations involve the formation of a stable complex between the analyte and a complexing agent (chelating agent). The principle is based on the formation of a 1:1 complex.
● Reactions: In complexometric titrations, the analyte forms a complex with the complexing agent, and the reaction is driven by the formation of a stable complex.
● Indicators: Complexometric indicators, such as Eriochrome Black T, are used to detect the endpoint in complexometric titrations. The indicator forms a coloured complex with metal ions, and the colour change signals the endpoint.
Comparison:
● Acid-base titrations involve the neutralisation of an acid and a base, while redox titrations involve electron transfer reactions. Complexometric titrations involve the formation of stable complexes between metal ions and complexing agents.
● Acid-base titrations use acid-base indicators, redox titrations use redox indicators, and complexometric titrations use complexometric indicators for endpoint detection.
● Acid-base titrations are commonly used for determining the concentration of acids and bases, while redox titrations are used for analysing redox-active species, and complexometric titrations are used for determining metal ions and hardness in water.
Discuss the applications of acid-base, redox, and complexometric titrations in various fields. Provide examples of real-world scenarios where each type of titration is employed for quantitative analysis.
Applications of Acid-Base, Redox, and Complexometric Titrations:
1. Acid-Base Titrations:
● Acid-base titrations are widely used in various industries and research fields for determining the concentration of acids and bases. They are particularly essential in analytical chemistry, environmental analysis, and pharmaceutical research.
● Example: In the pharmaceutical industry, acid-base titrations are used to determine the concentration of active pharmaceutical ingredients (APIs) and to analyse the acid or base content in drug formulations.
2. Redox Titrations:
● Redox titrations find applications in the analysis of various substances with redox-active properties. They are used to determine the concentration of reducing agents, oxidising agents, and metal ions.
● Example: In the environmental field, redox titrations are employed to analyse the concentration of dissolved oxygen in water samples. The titration involves the reduction of potassium permanganate by dissolved oxygen in the sample.
3. Complexometric Titrations:
● Complexometric titrations are widely used for the quantitative analysis of metal ions, particularly in the determination of water hardness and metal content in various samples.
● Example: In environmental monitoring, complexometric titrations are used to assess water hardness caused by calcium and magnesium ions. Ethylenediaminetetraacetic acid (EDTA) is commonly used as the complexing agent in this application.
4. Potentiometric Titrations:
● Potentiometric titrations are a variant of acid-base and redox titrations, where the endpoint is determined by monitoring changes in electrode potential rather than using indicators.
● Example: In the food industry, potentiometric titrations are used to determine the acidity of food products, such as vinegar, fruit juices, and dairy products.
In conclusion, acid-base, redox, and complexometric titrations are versatile and widely used techniques in quantitative analysis. Each type of titration has specific applications in different industries and research fields, enabling precise determination of concentrations and assessments of various analytes. These titration techniques play a crucial role in ensuring the quality, safety, and compliance of products and processes in various sectors.