Question

The van't Hoff factor \(i\) for an electrolyte which undergoes dissociation and association in solvent are respectively: (a) greater than one and less than one (b) less than one and greater than one (c) less than one and less than one (d) greater than one and greater than one

Short answer

(a) greater than one and less than one

Step-by-step solution

Understanding van't Hoff Factor for Dissociation

The van't Hoff factor, denoted as 'i', indicates the number of particles an electrolyte forms in solution. For a solution where dissociation occurs, molecules break apart into multiple ions. This results in the 'i' value being greater than one because one molecule of electrolyte produces more than one particle in the solution.

Understanding van't Hoff Factor for Association

In contrast, for a solution where association occurs, multiple molecules or ions come together to form a single larger particle. As a result, the 'i' value would be less than one because several particles combine to form fewer particles than there were initially.

Identifying the Correct Answer

Knowing the effects of dissociation and association on the van't Hoff factor, 'i', we can conclude that the correct answer is: (a) greater than one for dissociation (as the substance separates into more particles) and less than one for association (as multiple particles combine into fewer particles).

Key concepts

Electrolyte Dissociation

Have you ever wondered what happens when salt dissolves in water? Electrolyte dissociation is the process where compounds, such as salts, acids, and bases, dissolve in a solvent and split into ions. This is like breaking a bar of chocolate into individual pieces—each piece represents an ion. In physical chemistry, understanding this concept is crucial because it affects the behavior of solutions. Therefore, when electrolytes dissolve and separate into multiple ions, the van't Hoff factor (i) increases. It is greater than one because one unit of a substance forms several particles in the solution.

An everyday example would be table salt (NaCl) dissolving in water to produce sodium (Na+) and chloride (Cl-) ions. If you dissolve one mole of NaCl, you get one mole of Na+ and one mole of Cl-, resulting in an ideal van't Hoff factor of 2.

Electrolyte Association

On the flip side, electrolyte association is the reverse of dissociation. This happens when ions or molecules in solution combine to form larger molecules or complexes. Imagine inviting friends over and forming a group—a single, larger unit. In solution, when multiple particles bond together, they effectively reduce the number of free moving particles. This means the van't Hoff factor, in this case, becomes less than one. Less 'i' signifies that there are fewer particles than expected if no association occurred.

For example, when hydrogen ions and acetate ions in solution come together to form acetic acid, fewer particles result than the number that initially dissociated. This collective behavior is especially important in the study of solutions containing substances that can undergo both dissociation and association, influencing the solution's physical properties.

Solutions in Physical Chemistry

Diving deeper, solutions in physical chemistry are mixtures where one substance is uniformly distributed in another, which we call the solvent. The resultant homogeneous mixture exhibits a consistency where the solute cannot be distinguished by the naked eye. A sugar solution in water is a perfect illustration, where sugar is the solute and water is the solvent.

In the realm of electrolytes, the solvent usually permits the electrolyte to dissociate into ionized particles. The behavior and characteristics of solutions rely heavily on the nature of solutes and solvents at play. This uniformity is essential for predicting behaviors like boiling point elevation, freezing point depression, and how solutions carry electric current, all pivotal for applications in various technological and industrial processes.

Colligative Properties

When you examine the properties of solutions, there's a unique group called colligative properties. These properties depend only on the number of solute particles in a solution, and not on the nature of the solute itself. This means whether you dissolve sugar, salt, or any other substance, as long as the particle count is the same, the colligative properties will be consistent.

Key examples include boiling point elevation, freezing point depression, vapor pressure lowering, and osmotic pressure. All of which are influenced by the van't Hoff factor, because it measures the number of particles produced when a substance is dissolved. Remember, the more particles a solution has, the more significant the changes to these properties will be. So, a better understanding of the van't Hoff factor can give you a clear edge in mastering the behavior of solutions in various conditions and applications.