Abnormal Molar Masses

When it comes to defining abnormal molar mass, then it is characterised as an anomalous molar mass when the molar masses are greater or lower than the anticipated value when they are computed in chemistry. The colligative qualities are used to arrive at this result. In addition to raising the boiling point, decreasing the relative vapour pressure and depressing the freezing point of a substance, colloidal features include the ease of osmotic pressure. Using the Van’t Hoff factor, this method of calculating molar masses is inherently abnormal, as the label “abnormal” implies. We’ll find out.

Abnormal Molar Masses: A Brief Overview

As a preliminary step, we need to know how many solute molecules remain in a solution or a solvent after the association or dissociation of the solute molecules. The Van’t Hoff’s factor I was developed by Dutch scientist Van’t Hoff in an effort to learn more about the anomalies.

Particle Interactions in the Solvent

Abnormal molar mass is produced by some solute molecules that begin to interact with each other in a solution. As a result, a solution now contains fewer of these particles. In a solution, the colligative characteristics will change depending on the concentration of solute particles. As a consequence, the number of solute particles will begin to decrease.

The solute’s molecular mass is inversely related to its ability to bind with other substances. As a result, a rise in molecular weight is caused by a reduction in colligative characteristics.

As seen by the example, hydrogen bonding is diminished in benzene, which leads to the dimerisation of acetic acid and ethanoic acid in a benzene solution. The liquids with low dielectric constants are more likely to cause this problem. The molar mass is increased more than theoretically possible in this experiment.

Particle Dissociation in a Solvent

When a solute particle is dissolved in a solution, it may dissociate into more ions or particles. Consequently, the solution’s colligative characteristics will be enhanced as a result of this increase in solute particles.

Molar mass decreases with decreasing colligative qualities, as their inverse relationship dictates. This means that the molar mass will be smaller than planned. In this case, the molar mass will be abnormally high.

Example: Ions are generated when weak electrolytes are dissolved in water. Fluorine anion and hydrogen cation are the products of hydrofluoric acid dissociation in solution.

Van’t Hoff Factor for Abnormal Molar Masses

Van’t Hoff established a factor called the Van’t Hoff factor to better grasp the idea of anomalies. The molar mass of the solute is calculated using this factor to solve the issue of dissociation and association. The factor I is obtained when the normal mass or predicted value is divided by the abnormal mass.

i = Normal molar mass/Abnormal mass, or i = Observed or predicted colloidal characteristics/calculated colloidal properties or i= Total moles in the particles after dissociation or association/total moles before dissociation or association.

Abnormal molar mass formula

Solute association or dissociation begins with a written equation. Assuming that n is the number of dissociated particles and that is the degree of dissociation, then i = 1 + (n-1).

Thus 

Abnormal mass= molar mass/i

Where i is the van’t hoff factor.

Vapour Pressure

Relative reduction of vapour pressure refers to the phenomena where the addition of a non-volatile solute to a solvent causes the vapour pressure to decrease. He established that the mole fraction of a solute has a direct correlation to its vapour pressure, which in turn has a direct correlation to its solution pressure.

He found that the decrease in vapour pressure was caused mostly by an increase in the concentration of solute particles.

According to the rules of science,

Reduction in vapour pressure=Pure Solvent’s Vapour Pressure – Solution’s Vapour Pressure.

Thus the relative reduction is,

Reduction in vapour pressure/Pure Solvent’s Vapour Pressure

When a non-volatile solute is introduced to a solvent, the solute’s vapour pressure drops. In general, the boiling point of such a solution is higher than that of the pure solvent it is mixed with. This is because the solution’s temperature strongly influences the pressure of vapour. The temperature of the solution must rise in order for it to boil. This process is known as boiling point rise.

Conclusion

Some solute particles have been shown to modify their molar mass and colligative properties through association or dissociation in solution. The number of solute to solvent particles in a solution determines a property known as a ligand-solvent property ratio. The Van’t Hoff factor may be used to gauge the degree to which particles are associated or dissociated.

Jacobus Henricus Van’t Hoff, a Dutch physical scientist who won the first Nobel Prize in chemistry, is the inspiration for this factor’s name. For electrolytic solutions, the Van’t Hoff factor’s computed value is often lower than the predicted value (due to the pairing of ions). The divergence increases with increasing ion charge.