Non Aqueous Titration: Overview, Questions, Preparation

Solvents that are used in non-aqueous titrations are known as non-aqueous solvents. There are 4 types of solvents used in such titrations. These include:

1)  Aprotic solvents: These are chemically inert in nature and neutral in charge. Examples include benzene and chloroform. These are added to ionising substances which help in sharpening the endpoint during titration.

2)  Protogenic solvents: These solvents are acidic and readily donate protons. These are used to increase the basicity of weak acids and enhance the strength of weak bases. Examples include sulphuric and acetic acid.

3)  Protophilic solvents: These solvents are basic, and are proton acceptors. They react with acids and form solvated protons. Examples include liquid ammonia and amines.

4)  Amphiprotic solvents: These include the properties of both protogenic and protophilic solvents. Examples include alcohols and acetic acid.

Detection of Endpoint

Indicators used for non-aqueous titrations are:

1)  Crystal Violet: It gives violet colour in a basic medium and yellowish-green in acidic. It is widely used for the titration of pyridine

2)  Oracet Blue B: Blue colour in basic medium and pink in acidic

3)  Alpha naphtholbenzein and quinaldine red are also used as indicators

1)  It is a very simple, qualitative and highly accurate method.

2)  Organic acids and bases, which are insoluble in water, are soluble in non-aqueous solvents.

3)  It is useful for titrations of very weak acids and bases where water cannot be used.

4)  It can be used in the titration of a mixture of acids as well.

5)  It is a very important procedure in pharmacopoeial assays.

6)  Substance compositions that cannot be separately determined in aqueous media can be titrated in a non-aqueous medium.

1)  Solvents are comparatively expensive and less stable than ones used in aqueous titrations

2)  Indicators have to be prepared in a non-aqueous medium

3)  Solvents require calibrations after each use

4)  Volatile solvents can pollute the environment

5)  This titration is non-specific; hence there are chances that impurities may interfere

Non-Aqueous Titrations for Classes 10, 11 and 12

Non-aqueous titrations are included in the syllabus of Class 10, 11 and 12. In Class 11, the chapter ‘Redox reactions’ covering hydrogen, s-block and p-block elements has a 16-mark weightage. 

Illustrated Examples

1. The theory as to why non-aqueous titration is required:

Following is a reaction where water is not a suitable solvent-

R-NH2 + H+ ⇌ R-NH3+

H2O + H+ ⇌ H3O+

Here, H3O+ competes with R-NH3+ due to which one does not get the correct endpoint. Hence the need for non-aqueous titration.

1. Non-aqueous titration of weak base:

Acetic acid is commonly used because it does not compete with weak bases for protons. Only a strong acid will protonate acetic acid, for example, perchloric acid. 

1. Non-aqueous titration of weak acid:

Sodium, lithium and potassium methoxide are commonly used titrants in non-aqueous titrations of weak acids. 

Q. What is a non-aqueous titration?

Q. What is the difference between aqueous and non-aqueous titration?

Q. Why is acidic anhydride used in non-aqueous titration?

Q. Titrations of which compounds are carried out using non-aqueous titration?

Q. Non-aqueous titration is based on which theory?