An Introduction
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
1. What exactly is a non-aqueous titration?
A non-aqueous titration is a type of chemical analysis where the substance being measured is dissolved in a solvent other than water. This technique is essential for compounds that are either insoluble in water or are too weakly acidic or basic to provide a clear result in a normal aqueous environment.
2. What is the main difference between aqueous and non-aqueous titration?
The key difference is the solvent used. In an aqueous titration, water is the solvent for the analyte. In contrast, a non-aqueous titration uses an organic solvent, such as glacial acetic acid, acetonitrile, or an alcohol, to dissolve the analyte before the titration begins.
3. Why is water specifically avoided as a solvent in non-aqueous titrations?
Water is avoided because it has an amphiprotic nature, meaning it can act as both a weak acid and a weak base. This property can interfere with the titration of very weak analytes by competing with them, which makes it difficult to detect a sharp and accurate endpoint.
4. What types of solvents are typically used in this method?
The choice of solvent depends on the substance being analysed. The main types include:
- Aprotic solvents: These are neutral and do not donate or accept protons (e.g., benzene, chloroform).
- Protogenic solvents: These are acidic and can donate protons, which enhances the basicity of a weak base (e.g., glacial acetic acid).
- Protophilic solvents: These are basic and accept protons, which enhances the acidity of a weak acid (e.g., pyridine).
- Amphiprotic solvents: These can both donate and accept protons (e.g., ethanol).
5. How is the endpoint determined in a non-aqueous titration?
The endpoint can be determined using two primary methods:
- Visual Indicators: Special indicators like Crystal Violet or Thymol Blue are used. Their colour change is distinct and visible in the specific non-aqueous solvent being used.
- Potentiometric Method: This instrumental method uses an electrode to measure the electrical potential of the solution. A sharp, sudden jump in the potential reading signals the endpoint of the titration.
6. Why is this technique so important for analysing very weak acids or bases?
Very weak acids and bases do not react completely in water, resulting in a gradual and unclear endpoint. By using a suitable non-aqueous solvent, the apparent strength of these weak substances can be increased. For instance, dissolving a weak acid in a basic (protophilic) solvent makes it behave like a stronger acid, allowing it to be titrated accurately.
7. What are some common real-world applications of non-aqueous titration?
This method is widely used, particularly in the pharmaceutical industry. Common applications include:
- Determining the purity and concentration of drugs that do not dissolve in water.
- Analysing medicinal compounds like ephedrine, codeine, and various antihistamines.
- Quantifying organic compounds like oils and fats.
- Differentiating and measuring mixtures of primary, secondary, and tertiary amines.
