Titration is also known as titrimetry is a quantitative and volumetric method for determining the concentration of an unknown solution using the concentration of a known solution in the presence of an indicator.
To determine the concentration of an analyte in a solution, it is necessary to slowly add a volume of titrant (typically with a burette) until the color of the indicator changes to indicate a chemical reaction.
In quantitative chemical analysis, there are four types of titrations in terms of their purposes and methods, such as acid-base titration, redox titrations, precipitation titrations, and complexometric titrations.
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What is acid-base titration?
As you know, there are a lot of different compounds, both organic and inorganic. With the help of titration, you can determine their acidic or basic properties.
An acid-base titration is a quantitative analysis technique for determining the concentration of an acid or base by neutralizing it with a standard solution of acid or base of known concentration (Molarity).
Acid-base titrations involve neutralizing acids and a base therefore is also known as neutralization titration. It depends on the analyte's chemical interaction with a standard reagent.
Three different theories have been proposed to characterize acids and bases Arrhenius theory, Bronsted-Lowry theory, and the Lewis theory of acids and bases.
What is the principle of acid-base titration?
The acid-base titration principle is based on the neutralizing reaction that occurs between acid and base.
ACID + BASE ⇒ SALT + WATER
Strong/ weak acids or bases are used in acid-base titrations. It is used to determine how much acid or base there is. It is also used to determine the strength of an unknown acid or base. It determines the pKa of an unknown acid or pKb of an unknown base.
Not every reaction can be called a titration. Consequently, a reaction can be considered a titration under certain conditions.
The conditions are listed below:
- The reaction must quickly.
- A stoichiometric reaction should take place.
- The change in free energy during the reaction must be sufficiently large.
- There should be a method to determine the completion of the result.
What is an example of acid-base titration?
One example of an acid-base titration is the standardization of a NaOH solution usingCH3COOH, where sodium hydroxide is used as the strong base and is added to the burette, and acetic acid is used as the weak acid and is added to the conical flask. Acetic acid dissociation rises when a strong base is introduced to a weak acid.
What is the classification of acid-base titration?
Acid-base titrations are classified into four categories such as strong acid and strong base, weak acid and a strong base, weak base and strong acid, and weak acid and weak base.
Strong acid-strong base titration:
Example: Titration of hydrochloric acid (HCl) which is a strong acid and sodium hydroxide (NaOH) which is a strong base.
Weak acid and a strong base titration:
Example: Titration of acetic acid (CH3COOH) which is a weak acid and sodium hydroxide (NaOH) which is a strong base.
Weak base and strong acid:
Example: Titration of ammonia (NH3) which is a weak base and hydrochloric acid (HCl) which is a strong acid.
Weak acid and weak base:
Example: Weak acid includes formic Acid (HCOOH), Acetic Acid (CH3OOH), etc, and the weak base includes Ammonium Hydroxide (NH4OH), Ammonia (NH3)
What are indicators in acid base titration?
Acid-base indicators are weak acid or weak base that changes color as the concentration of hydrogen (H+) or hydroxide (OH-) ions in an aqueous solution changes. However, unlike other acids, the acid and base form the indicator have unique colors.
Indicators are often used in applications that require pH changes, such as titrations, pH tests, and science presentations because the color of the indicator depends on the pH of the solution.
The pH range of an indicator, which is dependent on the acid strength of the indicator, is its most important characteristic. The range of pH values over which an indicator changes color from its acid form to its base form is known as the indicator's pH range.
It extends from the highest pH, where only the acid form is visible, to the lowest pH, where only the basic form is visible. The indicator is insensitive to pH changes outside its range because it does not change color at these pH values.
Phenolphthalein and methyl orange are the two most common indicators used in the acid-base titration. Litmus is probably the best-known pH indicator. Common acid-base indicators include methyl red, thymol blue, bromocresol green, phenol red, etc.
What is the equivalence point in an acid-base titration?
The equivalence point is the point in a titration where the amount of titrant added is just enough to make the analyte solution completely neutral. In an acid-base titration, the equivalence point, moles of base = moles of acid, and the solution only contains salt and water. The endpoint of a reaction is the moment at which the reaction is completed.
It is essential to remember that endpoints and equivalence points may not be the same. As the equivalence point is determined by the stoichiometry of the reaction, whereas the endpoint is just the change in color of the indicator.
Usually, the endpoint can be determined only after the addition of a slight excess amount of the titrant. If the endpoint is different from the equivalence point, then it amounts to an error in the experiment.
Key terms used in acid-base titrations:
- Burette
A graduated glass tube having a tap at one end is used for titration to administer known volumes of liquid.
- Analyte
A substance whose quantity/concentration is to be determined.
- Titrant
A solution with a known concentration is filled in the burette that is added to another solution to find out the concentration of a second chemical species.
- Buffer
A solution consisting of an acid and its conjugate base is used to control the pH of a solution.
- pH
A measure of the hydrogen ion concentration is equal to - log [H+].
- pKa
The pKa value describes the acidity of a certain molecule. The strength of an acid is determined by how tightly a proton is retained by a Bronsted acid.
Frequently Asked Questions (FAQ):
What is the titration curve in chemistry?
The plot of the pH of the analyte solution vs the volume of titrant applied added as the titration progresses.
Why is acid-base titration important?
The main purpose of a strong acid-strong base titration is to determine the concentration of an acid solution by titrating it with a solution of known concentration, or vice versa until neutralization occurs. Therefore, the reaction between a strong acid base and a strong base will produce water and salt.
What are the steps of acid-base titration?
The steps of acid-base titration are: selection of titrant and the titrate, selection of normality of titrate, select the amount of liquid you wish to pipette, selection of indicator, note the endpoint when solution changes color, and calculate the normality of the titrant using the final reading.
Which indicator is used in acid-base titration?
Common acid-base indicators include methyl red, thymol blue, bromocresol green, phenol red, etc. Phenolphthalein and methyl orange are the two most common indicators used in the acid-base titration.
Litmus is probably the best-known pH indicator. Phenolphthalein is chosen because of its pH-dependent color change between 8.3 and 10. It shows pink in basic solutions and colorless in acidic ones.
Why is NaOH used in titration?
In a titration, sodium hydroxide is used if the unknown sample solution is acidic, as bases are utilized to neutralize acids.
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References:
- Wikipedia contributors. "Acid–base titration." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 7 May. 2022.
- GH Jeffery, J Bassett, J Mendham, RD Denney, Vogel's Textbook of Quantitative Chemical Analysis, 5th ed, 1989, Wiley, NY.
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