Some terms involved in Titrimetric Analysis:

Standard Solution:

The solution of accurately known strength is called the standard solution. Standard solutions are expressed by normality (N), molarity (M) etc.

Titrand & Titrant:

In titrimetric analysis the regent of known strength is called ‘Titrant’ and the substance being titrated is called ‘Titrand’. ‘Titrant’ taken in Burette and ‘Titrand’ taken in conical flask.

Example: If a known volume of NaOH solution is titrated with 0.1N HCl, then NaOH solution called ‘Titrand’ and HCl solution called ‘Titrant’.

Titration:

The process of adding standard solution to an unknown solution until the reaction is complete i.e. until the end point is achieved is termed as titration.

Equivalence/End point:

The point at which all the reagent of unknown solution (Titrand) react with known solution (Titrant) is called ‘Equivalence’ or ‘End point’.

At the end point, titration is detected by some physical change (usually color change) produced by indicator.

Indicator:

Indicator is a standard solution, which changes its color at the end point of a titration, or indicator is an organic dye that signals the end point by visual change in color.

Actually indicator formed a complex with excess Titrant, which added after the end point and change their color. For example-

Phenolphthalein in acidic solution

No color change

Addition of base excess than end point

Phenolphthalein in basic solution

Color change due to Phenolphthalein formed complex with base

Titration error:

100% accurate measure is impossible. Practical value and theoretical value is never same.

So, the difference between the theoretical value and practical value of a titration is known as Titration error.

i.e. Titration error = Theoretical value – Practical value.

Example: If the theoretical value of a titration is 5 but the examination value or practical value is 4.91.

Then titration error = 5 – 4.91

= 0.09

Condition of titrimetric analysis:

For use in titrimetric analysis a reaction must fulfill some conditions. They are as follows –

1.Chemical equation:

There must be a simple reaction, which can be expressed by a chemical equation. The substance to be determined should react completely with the reagent in stoichiometric (molar basis) or equivalent proportions.

NaOH + HCl NaCl + H₂O

2.Fast:

The reaction should be relatively fast. In some cases the addition of a catalyst may be necessary to increase the speed of a reaction.

3.Alteration of physical condition:

At the end point there must be a change in some physical condition.

4.Indicator:

An indicator should be available which, by a change in physical properties (color or formation of a precipitate), should sharply define the end point of the reaction.