Non aqueous titration principle solvents types and examples
Water can behave as a weak acid and a weak base. If we are titrating a very weak acid or weak base in an aqueous solution, then it is possible that it can compete with weak acid or base with regard to proton donation and acceptance.
Non-Aqueous Titration Theory Example
\[H_{3}O^{+}\] can compete with \[RNH{_{3}}^{+}\]. If it happens then we don’t get the correct endpoint by titration. A general rule is that acids with\[pK_{a}>7\] and bases with \[pK_{a}>7\] cannot be determined accurately in an aqueous solution. So, for titration of weak acids or bases, we use non-aqueous solvents. Many organic solvents such as acetone, alcohol, etc. can easily replace water as they compete less effectively with analytes for proton donation or acceptance. Reactions which occur in non-aqueous titrations can be explained by Bronsted -Lowry theory and its definition of acids and bases.
Types of Non-Aqueous Solvents Used in Non-Aqueous Titration
Following four types of solvents are used to dissolve analytes in non-aqueous titrations –
Aprotic Solvents
Protophilic Solvents
Protogenic Solvents
Amphiprotic Solvents
Aprotic Solvents– These are chemically inert substances such as benzene, chloroform, etc. these are added to ionizing substances to depress solvolysis of the neutralization product which in result sharpening the endpoint. Examples – benzene, toluene, carbon tetrachloride, etc.
Protophilic Solvents– These are basic in nature and react with acids to form solvated protons. A strong protophilic solvent changes the weak acids to strong acids.
Examples– liquid ammonia, amines, ether, etc.
Protogenic Solvents– These are acidic substances and readily donate the proton. These are used to increase the basicity of weak acid. They show a leveling effect on bases.
Examples- sulfuric acid, formic acid, etc.
Amphiprotic Solvents– These solvents have properties of both protophilic and protogenic solvents. Examples – alcohol, acetic acid, etc.
Advantages of Non-aqueous Titrations
Non-aqueous titration has the following advantages -
It is useful for the titrations of very weak acids or bases.
Many organic acids which are not soluble in water, can be dissolved in non-aqueous solvents. Thus, titration of these organic acids is very easy.
It can be used for titration of mixtures of acids as well.
These titrations show sharp end points with internal indicators.
It is a simple, qualitative, and selective method.
It is a highly accurate method.
Preferably non-aqueous titration is used for biological matters.
It is very important in pharmacopoeial assays.
Applications of Non-aqueous Titration
Non-aqueous titration has various uses in numerous fields. Especially in the field of medicine, non-aqueous titration is very useful. We have listed here a few applications of non-aqueous titration -
Non–aqueous titration is used to know the purity of assays.
It is used for the determination of concentration expressions.
It is used in the determination of hydrophobic compounds, phenobarbitone, diuretics, steroids.
It is used in the determination of the composition of antitubercular drugs and adrenergic drugs.
Disadvantages of Non-aqueous Titration
Non–aqueous titration has the following disadvantages -
Solvents used in non-aqueous titration are not stable compared to aqueous solvents.
In a non-aqueous titration, non-aqueous solvents are required calibration after every use.
In non-aqueous titrations temperature corrections are necessary.
If you want to know more about titration then go through the articles Mohr salt titration with \[KMnO_{4}\] precipitation titration, oxalic acid titration with \[KMNO_{4}\], etc. available on Vedantu. You can register yourself on Vedantu or download the Vedantu learning app for more such articles, NCERT Solutions, study material, mock tests, etc.
FAQs on Non Aqueous Titration in Acid Base Analysis
1. What is non aqueous titration?
Non aqueous titration is a type of acid–base titration carried out in a solvent other than water to determine weak acids or weak bases that cannot be accurately titrated in aqueous medium. It is mainly used when:
- The analyte is insoluble in water.
- The substance is a very weak acid or weak base in water.
- Water interferes with the reaction or causes hydrolysis.
2. Why is non aqueous titration used instead of aqueous titration?
Non aqueous titration is used when aqueous titration fails to give a sharp and accurate end point due to weak ionization or poor solubility in water. It is preferred because:
- Weak acids/bases show enhanced strength in suitable non-aqueous solvents.
- Some organic compounds are insoluble in water.
- Water may cause side reactions such as hydrolysis.
- Sharper end points are obtained with suitable indicators.
3. What are the types of non aqueous solvents used in titration?
Non aqueous solvents are classified into protogenic, protophilic, amphiprotic, and aprotic solvents based on their proton-donating or accepting ability. The main types are:
- Protogenic solvents (acidic): donate protons, e.g., sulfuric acid.
- Protophilic solvents (basic): accept protons, e.g., liquid ammonia.
- Amphiprotic solvents: both donate and accept protons, e.g., methanol.
- Aprotic solvents: neither donate nor accept protons, e.g., benzene, chloroform.
4. What is the principle of non aqueous titration?
The principle of non aqueous titration is based on the acid–base reaction occurring in a solvent that enhances the acidic or basic properties of the analyte. In a suitable non-aqueous solvent:
- Weak bases behave as stronger bases in acidic solvents.
- Weak acids behave as stronger acids in basic solvents.
- A clear equivalence point is obtained due to improved ionization.
B + HClO4 → BH+ClO4-.
5. Which indicators are used in non aqueous titration?
Indicators used in non aqueous titration are acid–base indicators that function properly in organic solvents. The choice depends on the solvent and titration type. Common indicators include:
- Crystal violet
- Malachite green
- Azoviolet
- Thymol blue (in some systems)
6. How do you perform a non aqueous titration?
Non aqueous titration is performed by dissolving the analyte in a suitable non-aqueous solvent and titrating it with a standard solution until the end point is reached. The general steps are:
- Dissolve the sample in a suitable solvent (e.g., glacial acetic acid).
- Add a few drops of a suitable indicator.
- Titrate with standard HClO4 or other appropriate titrant.
- Note the color change at the end point.
- Calculate concentration using the titration formula: M1V1 = M2V2 (for 1:1 reactions).
7. What is an example of a non aqueous titration reaction?
An example of non aqueous titration is the titration of aniline with perchloric acid in glacial acetic acid. The reaction is:
C6H5NH2 + HClO4 → C6H5NH3+ClO4-
- Aniline acts as a weak base.
- Perchloric acid acts as a strong acid in acetic acid medium.
- A sharp end point is observed using crystal violet indicator.
8. What is the difference between aqueous and non aqueous titration?
The main difference between aqueous and non aqueous titration is the solvent used and the strength of acids and bases in that medium.
- Aqueous titration: Uses water as solvent; suitable for strong acids and bases.
- Non aqueous titration: Uses organic or non-water solvents; suitable for weak acids/bases.
- Aqueous systems may give poor end points for weak electrolytes.
- Non aqueous systems enhance ionization and give sharper end points.
9. What are the advantages of non aqueous titration?
The main advantages of non aqueous titration are improved accuracy for weak acids and bases and better solubility of organic compounds. Key benefits include:
- Sharp and clear end points.
- Enhanced strength of weak electrolytes.
- Reduced interference from water.
- Suitable for pharmaceutical and organic compounds.
10. What are the limitations of non aqueous titration?
The main limitations of non aqueous titration are the need for pure solvents and careful handling due to moisture sensitivity. Important limitations include:
- Non-aqueous solvents can be expensive.
- Solvents like glacial acetic acid are hygroscopic and absorb moisture.
- Some solvents are toxic or volatile.
- Standardization of titrants is required frequently.
