Ionic Strength Formula

What is the Ionic Strength Formula?

The ionic strength of a solution is defined as the quantity of ion concentration in the solution. It can be expressed as ‘I.' The ion activity can be affected by it and is denoted with the ion interaction with water, including other ions in the solution. To compute half of the total concentration of every ionic species, the ionic strength formula can be used.

What is Ionic Strength?

Ionic strength is known as the measure of a concentration of ions present in a specific solution. Ionic compounds may certainly dissolve in water. And, on dissolving in water, they dissociate into ions.


Moreover, the total electrolyte concentration present in the solution contains an effect on significant properties like the solubility of different salts or the dissociation constant. Furthermore, ionic strength happens to be one of the major characteristics of a solution that has dissolved ions.

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The concept of ionic strength was formulated in 1921 by scientists Randall and Lewis. This concept is completely based on dissociation, which involves acid, bases, and salts in the presence of an aqueous solution. Knowledge of ionic strength is essential to chemists.


This is due to the ions having an electrical charge, which can either attract or repel each other. Moreover, this repulsion and attraction result in specific behavioural ways of ions. Furthermore, ionic strength can be representative of the interactions occurring between the ions of solutions and the ions present in water.

Ionic Strength Formula Computation

The formula of ionic strength or ionic strength equation can be given as:

I = \[\frac{1}{2}\] \[\sum_{1}^{n}C_{i}Z_{i}^{2}\]


Where, Ci – ionic concentration and Zi – ion charges

Ionic Strength Examples

Problem 1: Calculate the ionic strength of the KCl compound if its concentration is 2 M.


Answer: Calculating the ionic strength of a solution is shown below.


Given that:


Ions

Z

C

Z2

K+

1

2

1

Cl-

1

2

1


The Ionic Strength Can be Given as:


I = \[\frac{1}{2}\] [(2x1)+(2x1)] = 2


Problem 2: Calculate the ionic strength of K2SO4.


Answer: Calculating the ionic strength of a solution is shown below.


Given that:


Ions

Z

C

Z2

K+

1

2

1

SO4-2

2

1

4


The Ionic Strength Can be Given as:


I = \[\frac{1}{2}\] [(2x1)+(1x4)] = 3

FAQs (Frequently Asked Questions)

1. Give the Importance of Ionic Strength?

Answer: The ionic strength plays an essential role in the Debye - Hückel theory. Moreover, the Debye - Hückel theory explains the strong deviations from the ideality, which happen in ionic solutions.

2. Give the Considerations for Ionic Strength?

Answer: Non-ideal solutions refer to those solutions, which do not follow any ideal behaviour. An example can be solutions where one should consider the interaction forces. Besides, the usage of a unit of molality (mol/kg of H2O) occurs rather than molarity.

3. Explain If Ionic Strength is Synonymous With pH?

Answer: Ionic strength generally depends on the difference in the electronegativity of the attracted ions as the difference in the electronegativity increases the strength. At the same time, pH means hydrogen ion concentration, which denotes the alkalinity or acidity of the solution as per the pH value.

4. Give the Ionic Strength Effect on the Rate of Reaction?

Answer: The specific question concerns the kinetic salt effect, which is concerned with how the presence of ions in aqueous solutions affects processes that are not themselves part of the reaction. This effect comes into existence when the participants of a reaction, the intermediates or reactants, have a charge.


Ionic strength is given as a measure of the total dissolved salt ions in the solution. Ions in the solution can be attracted to the other ions of the opposite charge, and they are shielded by this attraction. For instance, let us say one of the reactants in the reaction involving two reactants holds a positive charge.