Van’t Hoff Factor, Characteristics, Association, Dissociation

Van’t Hoff Factor: This factor measures the amount of particles formed when a substance is dissolved compared to its mass concentration.

'I' refers to the effect of solutes on solution collation properties.

For example, the Van't Hoff factor describes how non-electrolytic substances dissolve in water. Van't Hoff factors describe how substances associate with or dissociate from solutions. In contrast, the value of i equals the number of ions in one formula unit when an ionic compound dissolves in water.

Since CaCl ₂ dissociates into one Ca ²⁺ ion and two Cl ^– ions, the Van't Hoff factor should be 3. Still, some ions associate with each other in the solution, decreasing its particle number.

In his first Nobel Prize in chemistry, Jacobus Henricus Van't Hoff, a Dutch physical chemist, won the award. A measurement of the Van’t Hoff factor for electrolytic solutions is usually lower than a predicted value (due to the pairing of ions). The greater the charge on the ions, the greater the deviation.

Characteristics of Van’t Hoff Factor

By mixing the particles with the substance's mass concentration, the Van't Hoff factor shows how solutes influence the solution's colloidal properties.

A specific non-electrolytic chemical dissolve in water with a Van't Hoff constant value of 1. The value of 'i' represents the total number of ions in the single formula unit of the ionic molecule.

Taking CaC ₂ as an example, we can see that it contains an optimum Van't Hoff factor of approximately 3 as it gets dissociated into two Cl ^– ions and one Ca ²⁺ ion. However, a few of these ions within the solution form associations, resulting in an overall decrease in particle solution.

Effects of Association/Dissociation

• An association is the joining of two or more particles into one.
• The dimerisation of carboxylic acids in benzene is an example of two particles interacting.
• A molecule dissociates into multiple ionic entities when it undergoes dissociation.
• In water, sodium chloride (NaCl) dissociates into Na+ and Cl ^– ions.

The following table shows how the association or dissociation of a solute affects the solution, the colliding properties, and the Van't Hoff factor.

Also Check – Bond Order Formula

Van’t Hoff Factor for the Association Solute

When the ions of solute associate in the solution, they give values lesser than 1. As an example, dimerisation of acetic acid in the presence of benzene causes the acetic acid to dimerize into two molecules that are then associated with ions. Therefore, the Van’t Hoff factor is less than 1.

Also Check – Tungstic Acid Formula

Van’t Hoff Factor for the Dissociation Solute

In a solution, solute particles give values greater than 1. For instance, when NaCl dissolves in water, it breaks down into Na ⁺ and Cl ^- ions.

Abnormal Molar Masses

The theoretical values of molecular mass, calculated from the collinear properties of solutions, sometimes differ from experimentally measured values, which are often referred to as abnormal molar masses.

Solutes dissolve into ions when they are dissolved in a solvent, according to Van't Hoff. Because colligative properties depend only on the number of solute particles, dissociating solute molecules into ions affects the colligative properties by increasing the number of particles.

Also Check – Atomic Mass Formula

When 1 mole of NaCl is dissolved in 1 Kg of water, if all the molecules of NaCl dissociate in water, there will be one mole of Cl ^– ions and one mole of Na ⁺ ions in the resulting solution (a total of 2 moles of ions in the solution). By considering only 1 mole of NaCl in the solution, we can calculate the molar mass.

For some substances, the number of ions/molecules in a solution is typically less than the number of molecules. As long as substances dissociate in solution, their observed molar mass will always be less than their real mass, whereas as long as substances associate in solution, their real mass will always be less than their observed molar mass.