Compare and contrast acid-base redox and comple... - SS3 Chemistry Analytical Chemistry II: Quantitative Analysis Question

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.