Redox Titration

As the name suggests this Titration is an example of an oxidation-reduction reaction. The chemical reaction in this titration occurs through the transfer of electrons in the reactive ions of aqueous solutions. One solution in redox titration is a reducing agent, while the other is an oxidizing agent. In this, we aim to find out the concentration of the reducing or oxidizing agent. We generally prefer the equivalence concept as balancing a redox reaction is a hectic task. Redox titration is further classified on the basis of the reagent used. They are mentioned below:

• Permanganate Titration
• Dichromate Titration
• Iodimetric and Iodometric Titration

Permanganate Titration

Potassium permanganate is used as an oxidizing agent. It is kept in good condition by using dilute sulphuric acid.

MnO₄^– + 8H + 5e → Mn²⁺+ 4H₂O

Before the endpoint, this solution is colorless. Furthermore, potassium permanganate is used to calculate oxalic acid, ferrous salts, hydrogen peroxide, oxalates, and many other substances.

Dichromate Titration

In an acidic medium, potassium dichromate is undoubtedly used as an oxidizing agent. Furthermore, the acidic medium is maintained by the use of dilute sulphuric acid.

K₂Cr₂O7 + H₂SO₄ → K₂Cr₂SO₄ + H₂O + 6O

Iodimetric and Iodometric Titrations  

In this titration, we use iodine or iodine solution as a titrant. Iodine is used in two ways in these titrations:

Iodimetric Titration

In the case of Iodimetric Titration, the I₂ molecule is used as a titrant against a solution of a reducing agent which is of unknown concentration. In this I₂ is converted to iodide ion. The reaction is mentioned below.

l₂ + 2e^– → 2l^–                                …….. (reduction)

Iodometric Titration

In the case of Iodometric Titration, the I^– the molecule is used as a titrant against a solution of an oxidizing agent which is of unknown concentration. In this, I^– is converted to an Iodine molecule. The reaction is mentioned below.

2l^– → I₂ + 2e^–                      ……. (oxidation)

Precipitation Titration

This titration is based on precipitate production. In precipitation titration, we put two reacting chemicals into contact. For example: When silver nitrate solution is used, ammonium thiocyanate or sodium chloride solution is used. When it interacts, it produces a white precipitate of silver thiocyanate or silver chloride.

AgNO₃ + NaCl → AgCl + NaNO₃

This titration is often followed by Gravimetric Analysis Titration to calculate the concentration of ion present in the precipitate.

Gravimetric Analysis Titration

Gravimetric Analysis is a quantitative tool to measure the mass concentration of ion present in the precipitate. It involves the following steps:

• Step 1: After the reaction achieves the equivalence point, the precipitate is formed and this precipitate is collected as the sample.
• Step 2: The sample so collected is then dried and crushed into powder.
• Step 3: At this stage, Gravimetric Analysis is done by measuring the mass of the sample and finding out the percentage of ion present.

As we have talked about Equivalence Point in the above steps let’s learn about Endpoint and Equivalence Point.

Equivalence Point & Endpoint

Equivalence point is the point where titrant and analyte become chemically equivalent in terms of quantities. This doesn’t mean to become equal quantity. This means the stoichiometric ratio of titrant and analyte would be such that there is a complete reaction as per the stoichiometric balanced equation.

Endpoint is the point where the color change is observed after the reaction has happened. It is related to Equivalence Point but not the same. It comes after Equivalence Point.

Complexometric Titration

The development of an undissociated compound occurs most importantly in this titration. It is also more than only precipitation titrations. For Example: 

Hg²⁺ + 2SCN^– → Hg(SCN)₂

EDTA, or ethylenediaminetetraacetic acid, is an essential reagent that produces compounds with metals.

Volumetric Analysis Titration

Volumetric Analysis involves the calculation of the unknown concentration of an analyte when titrated against a standard solution of a titrant with a known concentration. In this case, the volume of the titrant and analyte both are known. There are some pre-requisite conditions for Volumetric Analysis which are mentioned below:

• The reaction should be of moderate rate means neither too fast nor too slow
• The equation for the reaction must be known.
• Endpoint for the reaction must be detectable.
• Any side reaction should not be there which interferes with the main reaction.

There are two basic components of a Titration

• Titrant: The solution whose concentration is known.
• Analyte: The solution whose concentration is unknown.

Standard Solution: The titrant is prepared from a solution of known concentration. This is called a standard solution. It is of two types, Primary and Secondary.

• Primary Standard Solution: This is prepared by dissolving a calculated quantity of solute in a known volume of solvent. It is highly pure.
• Secondary Standard Solution: This is prepared by comparing against the primary standard solution because in their original form they are not stable.

The characteristics of standard solution are

• Should be Pure
• Should be Stable
• High Molecular Mass
• There should be no change in its concentration with time.

Volumetric Analysis Titration is of three types Simple Titration, Back Titration, and Double Titration. Simple Titration consists of Acid-Base Titration, Redox Titration, Precipitate Titration, and Complexometric Titration. All these we have studied above. Let’s study Back Titration and Double Titration.

Back Titration

Back Titration is the type of titration in which the unknown concentration of analyte is found out by reacting the analyte with a known amount of extra reagent and the remaining reagent is titrated against the second reagent. It is used when the reaction is too slow or in case of weak acid or base when it becomes difficult to find out the Endpoint.

Double Titration

As the name suggests, in Double Titration two different solution of known concentration is used to find the unknown concentration of the sample. It is an Indirect Titration method that is used to find the concentration of analyte in Acid-Base titration. In this first titration is done to standardize a reagent using another reagent. Now this standardized reagent is used to find the concentration of the sample.

Besides the above mentioned there are some more types of titration mentioned below.

Gas Phase Titration

In Gas Phase Titration, the reactants are in the gas phase. It is based on the principle of Beer-Lambert’s law which states that the concentration of a solution is directly proportional to the absorption of light by it.

Zeta Potential Titration

Zeta Potential Titration is used for heterogeneous systems such as colloidal and suspension etc. In this, the charge carried by the particles of colloidal and suspension is measured and used for finding the concentration of the sample. The measurement of charge is called Zeta Potential.

Assay

Assay refers to the purity of the substance in titration. It helps in determining the concentration of the solution because the more concentrated solution the more accurate will be the titration. The purity can be measured by gravimetric or volumetric analysis.

Titration is the gradual addition of a known concentration solution (called a titrant) to a known volume of an unknown concentration solution until the reaction approaches equilibrium, which is sometimes shown by a color change. The titrant solution must satisfy the appropriate criteria to be used as a primary or secondary standard. Titration is a technique for determining the concentration of an unknown solution in a general way.