Titration is a method to estimate the strength of any given substance in analytical chemistry.
In labs, titrations are carried on routine basis by methods like acid base titration, redox titration, complexometry and precipitation.
Acid base titration is the most simple and widely applicable technique. It is used to estimate the strength of acids, bases and even salts.
Here an acid reacts with a base to form salt and water. This reaction is called neutralization reaction.
The pH at the neutralization point is 7.
In acid base titration a know quantity of acid is used to estimate an unknown quantity of a base and vice-verse. One of the reactant is take on a burrette and other in a beaker. The reactant from burrette is added drop buy drop while the beaker or flask is swirled till the end point is reached.
The reactant taken in burrete is called titrant while that taken in flask is called as titre
In between an indicator is used to indicate the end point of reaction in between acid and base. In modern labs instead of indicators, pH meters are used to indicate endpoint.
Even the substance which are not acidic or basic in nature can be converted to by use of some reactions and then estimated by means of back titration or reverse titrations.
Acid Base Titration: 5 Types
These are normal titration between acids and base dissolved in water. Hence the name aqueous titration. They are prominently used in academic labs and for standardization.
1) Strong acid V/s strong base: Here are strong acid reacts with a strong base to form salt and water. The reaction of this type is very fast and also complete. The reaction happens in stoichiometric means i.e. each molecule of acid reacts with corresponding molecule of base. At the end of reaction no molecule of acid or base exists as every molecule in the reaction has completely reacted to form salt. Hence the end point or equivalencepoint is precise and sharp.
Example of this types of acids are HCl, H2So4,HNO3, HBr, HClO4 (perchloric acid), H3PO4 etc. The examples of strong bases are NaOH, MgOH2, Al2OH3 etc.
Reaction . HCl+NaOH—————-> NaCl + H2O
Either the know quantity of acid is taken in burrete to react with unknown quantity of strong base in flask (beaker) or vice-verse.
The pH at end point is neutral i.e. 7. So indicator changing their color around pH 7 are used here.
2) Strong Acid v/s Weak Base: Here a strong base reacts with weak acid to form salt and water. But since the reaction uses strong acid, the pH at end point will be towards acidic i.e. below 7.
Reaction example. HCl+NH4OH—————–>NH4Cl + H2O.
Here the salt formed NH4Cl is slightly acidic in nature. So indicators changing color at lower pH’s are employed.
During reaction, know concentration of strong acid is taken in a burrette and allowed to react drop by drop with the base in a beaker.
3) Weak Acid V/s Strong Base: Here the reaction happens between a weak acid and strong base. The weak acid is taken in a beaker and known quantity of strong base is dropped from a burrete till the end point.
Reaction example: H2CO3+ NaOH————–>Na2Co3+H2O
The salt formed is slightly basic in nature so the pH at end point is above 7. The indicator used is one with change in color at higher pH’s.
4) Weak Acid V/s Weak Base: Here both acid and base are weak. So mostly they are avoided due to imprecise end points. At the end point, the pH will be 7 theoretically. But cannot be measured precisely as that in strong acid and strong base case. An extra amount of titrant is needed to reach the end point due to imprecise reaction.
The end point is neutral as the salt is neutral but due t excess titrant added the pH can be in favor of it.
Check the video below for method
B. Non-Aqueous titration:
These are routine methods of non-aqueous titration. Here instead of water as solvent glacial acetic acid is used to make the reactants. They are similar to above types of acid base reactions. Since many drugs are water insoluble and slighlty acidic or basic, they are analyzed by non-aqueous titrations.They are extensively used for quality control and analysis of drugs.