Analysis plays a key role in evaluation of any compound for its quality and quantity.
It helps us to keep a check on the quality, safety of drugs, food, chemicals and other important substances.
Titration is a one of the important methods of analytical chemistry to evaluate chemical substances.
It is a method of analysis wherein a substance under test is allowed to react with known compound in a solution in presence of an indicator. There are different types of titration for different purposes. But all of them some common methodology.
During titration, the indicator indicates the end point i.e. it shows when the substance under test has been completely reacted with the analyzing regent. The reagent added to estimate is called titrant and the substance under estimation is called titrand.
The titrand is taken in a beaker while titrant is dropped from a burette till the end point is reached.
The sole purpose of titration is qualitative and quantitative estimation a given substance.
There are different types of titrations for analysis of compounds or substances.
These methods are economic, effective and also easy to perform.
The methods are also reproducible across all the labs. They have similar requirements and out puts if one follows a fixed procedure.
The different types of titration are
A) Based on method of titration:
They are of three types of titration based on the method used in process of titration.
The three types include
1. Direct titration: As the name indicates, it is basic titration. A known amount of titrant is added from a burrete to a titrand sample taken in a flask. Here one substance is analyzed for its quantity by another substance of known volume and concentration.
2. In-direct titration: Theoretically it is converting a substance into an acid and analyzing with a base. (also vice-verse). This is a methods extrapolated to use titration for non readily reactive substances. A substance can be weakly acidic and so it does not permit for precise analysis by direct titration. So first that substance is chemically altered to be more reactive in acidic or basic form and then analyzed by adding a titrant.
3. Back titration: This methods is also suitable for weakly reactive or non-reactive substance estimation. Here a substance is allowed to react with an excess and known quantity of a base or an acid. The remnant excess base or acid is estimated by a known quantity of acid or base receptively. It is called back titration as we are estimating a substance which was added by us.
B) Based on the nature of solvents and chemical reaction:
The titrations can also be classified based on nature of solvents used.
Based on the solvent used they can be classified as aqueous and non-aqueous types. Further based on the nature of chemical reaction they are classified as below
1. Aqueous titrations:
- Acid base titrations.( neutralization): An unkown sample of acid is estimated with a known quantity base or vice-verse. The end result reaches neutral point at pH-7 and in most cases salt is formed.
Check out Types of acid base titration for more.
- Redox titrations: The full name is oxidation-reduction titration. Here a reducing agent is allowed to react with an oxidizing agent till end point. The common oxidizing agents used are Potassium permanganate, bromine, cerium etc.
- Complexometric titrations: As the name indicates, the end point is seen by formation of a complex molecule. Here titrant and titrand react to form a complex till end point is reached. Once complex is formed, the complex is stable and not further reaction takes place. The reaction depends up the chelating agents ability to form complex with the sample under test. Example of chelate is ethylene tetra-acetic acid (EDTA)sodium salt.
- Precipitation titrations: The reaction occurs by formation of a solid precipitate at the bottom of flask. Here titrant reacts with titrand to form an insoluble precipitate. Example for such reaction is Silver nitrate with Ammonium chloride. The reaction forms a white precipitate of silver chloride.
2. Non-Aqueous titrations.
a) Acid base titrations.(neutralization): Here the reaction occur in organic solvents like glacial acetic acid and the acid used is perchloric acid (HClO4)
b) Redox titrations. Here the reaction is done as iodometry or iodimetry. Iodine is used as oxidising agent and reducing agent is thiosulphate.
c) Iodometry:Here the sample made to release iodine from within and this released iodine is measure with sodium thiosulphate as reducing agent.
d) Iodimetry: Here the sample under test is measured with a known concentration of Iodine.
These are similar to aqueous titrations but here instead of water as solvent, organic solvent is used.
C) Based on strength of reagents used:
The chemical reaction involved in titration is the main principle of titration. But the chemical reactions also depend on the nature and strength of the reagents used in the reaction.
So acid base titrations or the neutralization reactions are also further divided as
- Strong acid v/s Strong Base: Here both acid and base are strong. Ex: HCl v/s NaOH. Here the end point would be at an exact pH of 7. The salt formed in reaction would be neutral.
- Strong acid v/s Weak Base: A strong acid reacts with weak base. Ex: HCL v/s NH4OH. Here the end point would towards acidic pH i.e. below 7. The salt formed in the end would be slightly acidic.
- Weak acid v/s Strong Base: A weak acid reacts with strong base. Ex: Acetic acid v/s NaOH. Here the end point would be tilting towards basic pH i.e. above 7. The salt formed during neutralization would be slightly alkaline.
- Weak acid v/s Weak Base: Reaction between weak acid and weak base. Ex: Acetic acid v/s NH4OH. The end point would have a pH of 7. Here the salt formed as final product would be neutral.
Calculation: All the processes of titration are noted in a chemistry lab report manually. This includes the molar concentration of solutions, their volumes, indicators, formulas etc. This helps to calculate final values.