Chrominfo: What is the first equivalence point in titration?

Titration is a technique for determining the concentration of an unknown analyte (Titrand) using a known concentration solution (Titrant). The acid-base titration is a type of quantitative method for determining acid or base concentrations by neutralizing with a known concentration of acid or base. Generally, an indicator is used to detect the endpoint of the titration, which changes the color of the solution.

The point in the titration at which the amount of titrant added is sufficient to neutralize the analyte solution is referred to as the equivalence point. At the equivalence point, the number of moles of the acid is equal to the number of moles of the product, resulting in the formation of a salt product and water.

The equivalence point, or stoichiometric point, is the point where adding enough base to neutralize the acid to form a salt. At the equivalence point, there are an equal amount of moles of acid and base.

First equivalence point in titration:

The first equivalence point is the point of the titration in which the first hydrogen ion H+ from the initial volume of acid is neutralized by the base employed as the titrant.

H2A + OH- →H2O+HA-

At the first equivalence point, one mole of acid reacts with one mole of the base.

An example of the first equivalence point in titration:

Titration of diprotic acids such as sulfuric acid (H2SO4) and carbonic acid (H2CO3). In water, a diprotic acid dissociates in two stages.

From the beginning to the first equivalence point, the equations for acid-base reactions between a diprotic acid, H2X, and NaOH base.

All H+ ions from the first dissociation have reacted with NaOH base at the first equivalence point, and all H+ ions from both reactions have reacted at the second equivalence point. Diprotic acid titration curves have two equivalence points due to the successive dissociations,