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.
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FAQs on Non – Aqueous Titration
1. What is the difference between aqueous and non-aqueous titration?
Before learning about their differences, let’s first understand the definition of Aqueous titration and to know the meaning of Titration.
A technique that is analytical in nature that is used to measure the concentration of any particular solution of the chemical is known as Titration. A particular apparatus is required in the process of Titration.
The techniques that are analytical which is used to describe the amount of the wanted substance in the sample that uses water as a solvent.
The main difference between Aqueous and non-Aqueous is in Aqueous titration, water is used as a solvent in order to dissolve analyte samples, and non-Aqueous uses a solvent that is organic.
2. What are the types of titration?
There are many types of titration which are discussed below:
Acid-Base- This type of titration is also known as neutralization titrations. In this, an unknown sample can be dissolved in water to know the amount of acid and base in the sample with the use of acid/base.
Redox- When a reducing agent reacts in an oxidation-reduction reaction with an oxidizing agent to allow us to know the amount of wanted substance in the sample.
Precipitation- In this, solid precipitate forms in the bottom level of the flask that is used for the titration. The analyte is an aqueous solution in this titration.
3. Write about the indicators used in non-Aqueous titration?
Indicators that are visual in nature turn out the most appropriate in a non-aqueous titration, to find the equivalence point or endpoint of the reaction. There are many indicators used in non-aqueous titration which are discussed below:
Crystal Violet- the most common indicator in non-aqueous titration is Crystal violet, which is used in glacial acetic acid as 0.5 % w/v solution.
Methyl Red- it is made in dioxin in a 0.2% w/v solution. The Color changes in the endpoint from yellow to red.
Thymol Blue- in multiple types of titrations, it is used commonly as a pH. indicator. In methanol, it is used as 0.2% w/v in it. Its color at the endpoint changes from yellow to blue.
4. What are the applications of non-aqueous titration?
Non-aqueous titrations have a large variety of applications in various fields. Some of them are listed below:
One of the major applications in non-aqueous titration is the pharmaceutical application. It is because non-aqueous titration tends to be very useful in the field of medicine.
To control the purity of various kinds of chemicals, non-aqueous titration is used.
In performing assays that allow defining the purity of compounds, it is used.
In determining the hydrophobic compounds, it is used.
In defining the composition of antitubercular drugs and adrenergic, it is used.
It is used to quantify the mixtures of the samples of primary, secondary, and tertiary.
5. What do you understand by non-aqueous acid/base titration?
Suppose you dissolve a sample in water, depending on its nature, a titration is done by using aqueous acid or aqueous base as a titrant. A glass pH electrode is used for indication.
Because of the nature of the sample, sometimes, aqueous titration can’t be done. Non-aqueous acid-base titration comes in use only when:
When the samples are either oils or fats
The substance which is of interest does not mix with water.
The components of acid-base mixtures should be defined in a separate way in titration.
To know more about it, try the material provided by Vedantu. NCERT Solutions for Class 12 Chemistry - Vedantu