Define Negative Correlation

 

Redox titration :-

Redox Titration is a laboratory method of determining the concentration of a given analyte by causing a redox reaction between the titrant and the analyte..

Redox Titration Example :-

Titration can be used to track and measure a species’ oxidation and reduction. The addition of thiosulfate (S2O3²–) to the solution, for example, can be used to monitor the oxidation of iodide (I–) to iodine (I2). Iodine will be reduced to iodide by the thiosulfate. The titration’s endpoint can be calculated by adding a starch indicator to the solution. When the blue starch indicator comes into touch with the iodine, it turns red.

Theory of redox indicators :-

A redox indicator is a molecule that changes colour when potential differences are changed. Colourimetric reagents that show a particular colour shift at a specific electrode potential are known as oxidation/reduction (redox) indicators. These are all reversible redox reactions in organic molecules. Nile blue, Anilinic acid, diphenylamine, eriogreen, m-cresol-indophenol, and methylene blue are among the examples.

The reduced and oxidised forms of a redox indicator molecule must exhibit different hues, and the redox process must be reversible. Furthermore, the oxidation-reduction equilibrium must be swiftly achieved. Redox indicators are only suitable for a few types of compounds:

In these titrations, free iodine is reduced to iodide ions, and iodide ions are oxidised to free.

l2 + 2e– → 2l–……………. (reduction)

2I– → I2 + 2e– ……………. (oxidation)

As an indicator, the solution is utilised. The iodometric titration uses free iodine, whereas the iodometric titration uses an oxidation agent to react and liberate free iodine.

Reduction :-

A substance can undergo reduction can occur via:

• The addition of hydrogen.
• The removal of oxygen.
• The acceptance of electrons.
• A reduction in the overall oxidation state.

Examples of the reduction reaction :-

NH3 + HCl  →  NH4Cl (addition of hydrogen)

2 Na + H2O →  2 NaOH (addition of electropositive element)

2 KClO3 → 2 KCl + 3 Cl2 (removal of oxygen)

H2S → H2 + S (removal of electronegative element)

Oxidation :-

The following points describe a substance that has undergone oxidation.

• The addition of oxygen.
• Removal of hydrogen which was attached to the species.
• The donation/loss of electrons.
• An increase in the oxidation state exhibited by the substance.

Examples of oxidation reactions :-

2 MgO + O2 → 2 MgO (addition of oxygen)

FeCl2 + 3/2Cl2 → FeCl2 (addition of electronegative element)

H2S + Cl2 → HCl + S (removal of hydrogen)

Hg2Cl2 → HgCl2 + Hg (removal of electropositive element)