Volumetric Titration

Aug 26, 2022, 16:45 IST

About Volumetric Titration

The process of determination of concentration of a solution of unknown concentration with the help of a solution of known concentration i.e., standard solution, is known as TITRATION.

Before approaching towards the depth of volumetric analysis one must know the following terms very clearly.

Many chemical reactions occur in the solution state and hence stoichiometric problems may sometimes involve different concentration terms of solutions to give an idea of amount of solute and solvent present in the solution. There are various ways to represent concentration of the solution as mentioned below. 

In a solution the designation of solute and solvent is often a matter of convenience, however many a times the one present in smaller quantity is termed as solute. Also, a solution may have more than one solute but solvent cannot be more than one.

All the concentration terms given below are applicable only when there is a homogenous solution or when solute completely dissolves in the solvent. 

Terms use in Volumetric Titration

The following concentrations terms are used to expressed the concentration of a solution. These are

1. Molarity (M)

2. Molality (m)

3. Mole fraction (X)

4. % calculation

5. Normality (N)

6. ppm

Please remember that all these concentration terms are related to one another Before discussing N one must have clear concept about equivalent weight 

Equivalent Weigh

Number of parts by mass of an element which reacts or displaces from a compound 1.008 parts by mass of hydrogen, 8 parts by mass of oxygen and 35.5 parts by mass of chlorine, is known as the equivalent weight of that element e.g.

equivalent weight is the ratio of atomic weight and a factor (say n-factor) which is in above three cases is their respective valencies. So, equivalent weight =  

In a similar way, the equivalent weight of acid/base is the ratio of molecular weight and the basicity/acidity and for oxidizing agents and reducing agent it is the ratio of molecular weight and the number of moles of electrons gained or lost. So in case of acid/base the n-factor is basicity/acidity (i.e. number of dissociable H+ ions/number of dissociable OH– ion and in case of oxidizing agent/reducing agent, n-factor is number of moles of electrons gained/lost per mole of oxidizing agent/reducing agent. Therefore, in general, we can write.

Equivalent weight (E) =  

No. of equivalents of solute =  

No. of equivalents of solute = No. of moles of solute  n-factor

 And also Normality = n-factor  molarity of solution

Volumetric Analysis with titration 

The process of determination of concentration of a solution with the help of a solution of known concentration (standard solution) is called titration.

Titration is divided into following four categories.

i) Simple Titration

ii) Double Titration

iii) Back Titration

iv) Iodimetric and Iodometric Titration

Simple Volumetric Titration

A known volume of the solution of unknown concentration is taken in a flask and required reagents are added to it. The solution of known concentration is added from the burette in the solution of unknown concentration till the latter reacts completely. This process is called titration. 

Double Volumetric Titration

If an aqueous solution contains a mixture of any two of the three NaOH, NaHCO3 and Na2CO3 and it has to be titrated against an acid HCl or H2SO4, it will require two indicators to determine the strength of the bases present. The two indicators used are phenophthalein and methyl orange.

Back Volumetric Titration

Let us consider that we have an impure solid substance ‘Z’ weighing ‘w’ g and we are required to calculate the percentage purity of ‘Z’ in the sample. We are also provided with two solutions ‘X’ and ‘Y’, where the concentration of ‘Y’ is known (N1) and that of ‘X’ is unknown. For the back titration to work, following conditions are to be satisfied