Acid-Base Titration

Acid-Base titration aims to find out the strength of an acid or base of unknown concentration using a base titrant for acid and an acid titrant for a base. Acidimetry is the measurement of acid strength using a standard solution of the base. Similarly, alkalimetry can be used to determine the strength of a base using a standard solution of an acid.

This titration is based on the principle of Neutralization Reaction. We know that when acid and base react, Neutralization Reactions occur.  We try to find how much titrant of known concentration is used to Neutralize the acidic or basic solution of unknown concentration present. In an acid-base titration, one solution is an acid and the other is a base. Furthermore, one is placed in a flask, while the other is placed in a burette and dripped into the flask until the titration reaches its endpoint. For Example: 

HA + BOH  →  BA + H₂O

where,

• HA is acid and A is a negative ion
• BOH is base and B positive ion

This titration is based on the neutralizing reaction between a base or an acidic and an analyte. In addition, a reagent is combined with the sample solution until it reaches the desired pH level. This type of titration is heavily reliant on the pH track or a pH meter.

Procedure for Acid-Base Titration

One should perform the Acid-Base Titration by following the below-mentioned steps:

• Step 1: Prepare the titrant of known concentration, acid titrant for a base solution, and base titrant for an acid solution.
• Step 2: Using Pipette measure the prepared titrant and pour it into a conical flask.
• Step 3: Add a few drops of an indicator to the flask.
• Step 4: Prepare a solution of the acid or base which is to be titrated and fill it in a burette.
• Step 5: Fix the burette in a stand clamp and add the solution of unknown concentration drop by drop into the conical flask which has the titrant.
• Step 6: When the reaction occurs, the color of the solution in the flask changes due to the presence of an indicator.
• Step 7: At this point note down the change in volume of solution from burette.
• Step 8: Perform the titration three times for accuracy.
• Step 9: After three times of titrations, do the necessary calculation with errors taken into account.

Selection of Indicator for Acid-Base Titration

The acid and base are of two types namely strong and weak depending upon the ability to dissociate ions. It is easy to achieve the endpoint in the case of strong acid and strong base but difficult in the case of weak acid and weak base. 

In case, we have to titrate a solution of weak acid of unknown concentration then we will use a strong base of known concentration as titrant because the conjugate of a weak acid is a strong base.

If we have to titrate a solution of a weak base of unknown concentration then we will use a strong acid of known concentration as titrant because the conjugate of a weak acid is a strong acid.

Here in both scenarios, methyl orange is added as an indicator which is orange in the acidic solution and yellow in the basic solution.

 Another indicator used is Phenophthalien which is colorless in acidic solution and pink in basic solution.

Titration is the gradual addition of a known concentration solution (called a titrant) to a known volume of an unknown concentration solution until the reaction approaches equilibrium, which is sometimes shown by a color change. The titrant solution must satisfy the appropriate criteria to be used as a primary or secondary standard. Titration is a technique for determining the concentration of an unknown solution in a general way.