Acid base titration-Working principle, Process, types and indicators

Learning objectives

In this article, the author has explained Acid base titration, its working principle types and process of acid base titration

Acid-base reactions are used to find the amount of acidic or basic substances. The solution with unknown molarity is the analyte. The analyte will react with the solution with known molarity.

Titration is a chemical analysis method used to determine the concentration of a particular analyte.

Titration, also known as volumetric analysis, is a method in which the titrant is added from a burette until the reaction is complete, and an indicator is usually employed to mark the endpoint of the reaction.

I have also written few titration related other articles, I am sure you would learn from these as well.

What is acid-base titration?

An acid-base titration is a quantitative analysis method used to determine the concentration of an acid or base by neutralizing the acid or base with a known concentration standard solution.

The concentration of a solution can be determined by knowing the acid and base dissociation constant. If the solution concentration is known, a titration curve can be used.

Principle of acid-base titration

In the theory of acid-base titration, the principle involves using a burette and pipette to determine the concentration of an acid or basic.

An indicator is a dye added to a solution to change its color. It is dissolved in the sample solution and can be used to detect the end of the titration.

Indicators used in acid-base titration:

The acid strength of the indicator is important in determining the pH range. The indicator changes color from acid to base when its in the range of pH values.

The acid form can only be seen at the highest pH, the base form can only be seen at the lowest. Since the indicator doesnt change color at certain pH levels, its not sensitive to changes outside of its range.

Classification of acid-base titration indicators

Acid-base indicators are generally classified into below listed three groups.

1. The phthaleins and sulphophthaleins: example-phenolphthalein indicator

2. Azo indicators: example- methyl orange indicator

3. Triphenylmethane indicators: for example- malachite green indicator

Selection of indicator in acid-base titration:

Different indicators are used in acid-base titrations. The selection of indicators depends on the type of titration and the range of the reaction.

  • Strong acid-strong base: Phenolphthalein is generally preferred due to color change seen more easily.
  • Weak acid-strong base: Phenolphthalein is more proffered for this titration because it changes sharply at the equivalence point.
  • Strong acid-weak base: Methyl orange is more proffered for this titration because it changes sharply at the equivalence point.
  • Weak acid-weak base: Because a vertical portion of the curve above two pH units is required, there is no indication is suitable for this titration.

Types of acid-base titration with their examples:

There are four different types of acid-base titration, which include strong acid-strong base, weak acid-strong base, strong acid-weak base, and weak acid-weak base.

Strong acid-strong base:

Its one of the easiest titrations to perform among the four forms of acid-base titrations. It involves the dissociation of a strong acid and a strong base in water, which results in a strong acid-strong base neutralization reaction. The equivalency point is reached when the moles of acid and base are the same and the pH is zero.

Weak acid-strong base

The direct transfer of the protons from the weak acid to the hydroxide ion is possible in this type of titration. The acid and base react in a one-to-one ratio when reacting a weak acid with a strong base. At the equivalent point of a weak acid-strong base titration, the pH is larger than 07.

Strong acid-weak base

The acid and base will react to form an acidic solution. A conjugate acid is formed which reacts with water to form a hydronium ion. At the point of a strong acid-weak base titration, the pH is less than 7.

Weak acid-weak base

The shape of a weak acids or bases titration curve depends on the acids or bases identity and the associated acid ionization constant. In the titration of a weak acid or a weak base, the pH gradually changes around the equivalence point, which is greater or less than 7.

Below are examples of these titrations.

  • Hydrochloric acid (HCl) and sulphuric acid (H2SO4) are two examples of strong acids.
  • Acetic acid (CH3COOH) and formic acid (CH2O2) are two examples of weak acids.
  • Sodium hydroxide (NaOH) and potassium hydroxide (KOH) are two examples of strong bases.
  • Ammonia and methylamine are two examples of weak bases.

Process of titration

First of all we need to arrange the following apparatus to perform acid-base titration.

  • Conical flask
  • funnel
  • beaker
  • pipette
  • burette
  • burette stand
  • Spatula
  • wash bottle
  • indicator
  • unknown solution
  • Standard solution

Then we need to clean all the apparatus using distilled water.

After then we need to fill the burette with a standardized solution, accurately measure the volume of the analyte, and add in the conical flask, also add a few drops of indicator using the pipette.

Titrate it with the standardized solution until the indicator changes color. When the indicator permanently changes the color, the endpoint reaches.

Repeat the titration at least three more times and record the initial and final readings in the observation table and calculate the value.