Question

Among the colligative properties of solution, which one is the best method for the determination of molecular masses of proteins and polymers? (a) osmotic pressure (b) lowering in vapour pressure (c) lowering in freezing point (d) elevation in boiling point

Short answer

Osmotic pressure is the best method for the determination of molecular masses of proteins and polymers.

Step-by-step solution

Understanding Colligative Properties

Colligative properties are properties of solutions that depend on the number of particles in a given volume of solvent and not on the nature of the chemical species present. The key colligative properties include osmotic pressure, lowering in vapor pressure, lowering in freezing point, and elevation in boiling point.

Analyzing the Methods

For large molecules such as proteins and polymers, which have relatively low molar concentrations in solution, the most sensitive and accurate colligative property to measure is the osmotic pressure. This is because osmotic pressure can be measured even for very dilute solutions where the other colligative properties would be too small to measure reliably.

Determining the Best Method

Since osmotic pressure measurements are highly sensitive and require only small quantities of the solute, they are the best method for determining the molecular masses of large molecules such as proteins and polymers.

Key concepts

Osmotic Pressure

Osmotic pressure is a fundamental concept when studying colligative properties and plays a significant role in determining molecular masses, particularly of proteins and polymers. It is defined as the pressure required to stop the flow of solvent molecules through a semipermeable membrane from a dilute solution to a more concentrated one.

Osmotic pressure (\( \text{Π} \) can be mathematically expressed by the van't Hoff equation, which is:
\[ \text{Π} = iMRT \
\]where \( i \) is the van't Hoff factor, \( M \) is the molarity of the solution, \( R \) is the gas constant, and \( T \) is the temperature in Kelvin.

This relationship is essential in biochemistry and medicine, as osmotic pressure is the driving force in many biological processes, such as nutrient absorption and waste removal in cells. When it comes to molecular mass determination, osmotic pressure becomes invaluable for measuring the molar masses of large and complex molecules like proteins, which are typically found in low concentrations in solution. Small changes in osmotic pressure can indicate the presence and concentration of these macromolecules, making it a precise tool for molecular characterization.

Molecular Mass Determination

The molecular mass of a substance is a critical parameter in understanding its chemical, physical, and biological characteristics. In the context of colligative properties, the most accurate method for determining the molecular mass of macromolecules, such as proteins and polymers, is through the measurement of osmotic pressure. This is largely due to the proportionality of osmotic pressure with the molarity of the solution, which directly involves the molecular mass of the solute.

For a solution containing a non-volatile solute, the osmotic pressure is measured to calculate the molar mass of the solute using the formula rearranged from the van't Hoff equation:
\[ M = \frac{\text{Π}RT}{i} \
\]In this equation, once the osmotic pressure (\( \text{Π} \) is determined, and if the van't Hoff factor (\( i \) is known (often 1 for non-electrolytes), the molecular mass (\( M \) is easily derived. Due to the high precision of osmotic pressure measurements, even in dilute solutions, this method is particularly advantageous for substances like proteins and polymers whose large size can render other colligative property methods less effective.

Proteins and Polymers

Proteins and polymers are macromolecules with high molecular mass, playing vital roles in both biological and industrial applications. Proteins, as the workhorses of living organisms, perform a myriad of functions, from catalyzing metabolic reactions to providing structural support. Polymers, composed of repeating structural units known as monomers, are ubiquitous in manufacturing and everyday products.

Understanding the molecular mass of these macromolecules is crucial for deciphering their functionality and behavior. For instance, in biology, the osmotic pressure technique applies to the study of proteins' role in maintaining the proper pressure balance across cell membranes – a concept known as osmoregulation. Similarly, in materials science, determining the molecular mass of polymers through osmotic pressure can influence the physical properties of materials, such as their strength, elasticity, and degradation rate.

For these reasons, determining the molecular mass of proteins and polymers through osmotic pressure is not only the most sensitive method but also provides insight into their intrinsic properties that govern their diverse roles. Due to the low concentrations at which these molecules are often studied, osmotic pressure offers the necessary sensitivity to yield accurate measurements, which is essential for applications in biochemistry and material sciences.