Introduction

Due to the large number of elements and chemicals existing in our environment, we have an excellent opportunity to learn about their qualities. It is necessary to investigate the many qualities of such stuff because this will make it easier to comprehend the nature and activity of these substances in the future. The determination of the molar mass of such materials is the most important step in learning about the many properties of these substances.

Every substance, regardless of whether it is in solid, liquid, or gaseous form, has a tendency to act in a specific way that is highly dependent on its properties. As a result, all liquid substances can be investigated in terms of their colligative properties. This is beneficial in the investigation of the vapour pressure of the solution. So, let’s look at the collapsing properties of matter and the calculation of molar mass as a starting point.

Molecular Mass: An overview

The molecular mass (m) of a given molecule is the mass of that molecule as measured in Daltons (Da or u). Because various isotopes of an element are present in distinct molecules of a chemical, different molecular masses can be seen between different molecules of the same substance. This quantity, defined by the International Union of Pure and Applied Chemistry (IUPAC), is the ratio of the mass of a molecule to the unified atomic mass unit (also known as the dalton). It is a unitless quantity. The molecular mass and relative molecular mass are not the same as the molar mass, but they are connected to it. molar mass is defined as the mass of a given material divided by the amount of a given substance, and it is expressed in gram per mole of a particular substance. When dealing with macroscopic (weigh-able) amounts of a substance, the molar mass is almost always the more appropriate number to use instead.

Colligative properties in brief

Colligative properties of a liquid are those properties of a liquid that are dependent on the number of solute particles present rather than the concentration of the solution. These characteristics are investigated in liquids. A drop in the relative vapour pressure of a solution is observed when a non-volatile solution is mixed with a volatile solution, based on these features of the solution.

This drop in vapour pressure may also be used to quantify and examine the properties of all liquid solutions, which is a useful tool in many fields of science. To be more specific, the colligative qualities of a solution are determined by the number of solute particles present in the solution. A derivative of the Latin word “Coligare,” the term “colligative” refers to the act of joining two or more things together.

Determination of molecular mass from various colligative properties

There are four colligative properties, which are as follows: a relative decrease in vapour pressure, an increase in boiling point, a decrease in freezing point, and a decrease in osmosis and osmotic pressures. The following conclusions can be drawn in relation to these characteristics:

Relative Lowering of Vapour Pressure

During the research, a French chemist identified a relationship between pressure of the solution, pressure of vapour of pure solvent, and the mole fraction of the solute (or solute concentration).

He also discovered that the concentration of solute particles is the primary factor in the reduction of vapour pressure. According to the laws proposed by scientists at the time, the decrease in vapour pressure equals the difference between the vapour pressure of pure solvent and the vapour pressure of the solvent. The ultimate molar mass of a solute may be determined by using this equation, which can be found here. 

(Psolvent = Xsolvent Posolvent)

Elevation of Boiling Point

When a non-volatile solute is introduced to a volatile solute in a solvent, the vapour pressure of the volatile solute tends to drop. It is important to note that the boiling point of such a solution is always higher than the boiling point of the pure solvent to which it has been added. This occurs as a result of the fact that the pressure of vapour increases in direct proportion to the temperature of a solution.

If the solution is to be boiled, it is necessary to raise the temperature of the solution. The phenomenon that causes the rising of boiling point is known as the elevation of boiling point. Both the solute particles and the vapour pressure present in the solvent have a role in producing this phenomenon.

T = iKbm is a mathematical formula.

where T denotes the temperature change, i component, known as the van’t Hoff factor, represents the number of particles into which the solute dissociates and m is the molality, which is defined as the number of moles of solute in one kilograms of solvent.

For water, Kb is equal to 0.5121oC/m, which is the molal boiling point constant.

Depression of Freezing Point

Decreasing the vapour pressure of a solution has the additional effect of decreasing the freezing point of the solution. This can be determined by determining the temperature at which a specific substance’s vapour pressure in both the liquid and vapour states equals zero. Similarly, to the boiling elevation point, the freezing point for a given dilute solution remains linearly proportional to the molality of the solute according to the rule of thermodynamics.

T = iKfm is a mathematical formula.

T represents the temperature change, i component, known as the van’t Hoff factor, represents the number of particles into which the solute dissociates and m is the molality, which is defined as the number of moles of solute in one kilograms of solvent.

Kf is the molal freezing point constant (for water, Kf = -1.86 oC/m) and is measured in degrees Celsius per metre square.

Osmosis and Osmotic Pressure

An example of osmotic pressure in a solution is extra pressure applied to the solution in order to prevent osmosis from occurring. As a colligative feature, it is dependent on the amount of solute molecules present rather than the identity of those molecules.

When applied to dilute solutions at a given temperature, osmotic pressure is directly proportional to the molarity (C) of the solution at a given temperature (T).

Π = C R T = (n2/V) R T

in which osmotic pressure is denoted by, C is the molarity, R is the gas constant, T is the temperature, V is a volume of solution in litres, and n denotes the number of molecules of solute

Since n2 = w2/M2, then Π V = w2RT/M2 OR M2= w2RT/Π V

Conclusion

As a result, we can determine the molecular weight of a drug by examining the collational properties of solutions in the laboratory. The three procedures outlined above present us with options that can be used depending on the type of chemical being measured, the nature of the solvent being used, and the level of precision necessary during the measurement.