Question

The Nernst distribution law \(K_{D}=C_{1} / C_{2}\) is not applicable if the solute undergoes (a) association in one of the solvents (b) dissociation in one of the solvents (c) association and dissociation in one of the solvents (d) none of the above

Short answer

The Nernst distribution law is not applicable in cases where the solute undergoes (a) association in one of the solvents, (b) dissociation in one of the solvents, and (c) association and dissociation in one of the solvents. Therefore, option (d) 'none of the above' is not correct.

Step-by-step solution

Identify assumption of Nernst distribution law

The Nernst distribution law is applicable if the solute does not undergo association or dissociation, that is, the solute concentration remains constant in either solvent.

Evaluate option (a): association in one of the solvents

If the solute associates (comes together to form a larger molecule) in one of the solvents, the concentration of the solute changes in that solvent. This violates the assumptions of Nernst distribution law, thus this option is a condition where the law is not applicable.

Evaluate option (b): dissociation in one of the solvents

If the solute dissociates (splits into smaller molecules or ions) in one of the solvents, the concentration of the solute increases in that solvent. This also violates the assumptions of Nernst distribution law, thus this option is also a condition where the law is not applicable.

Evaluate option (c): association and dissociation in one of the solvents

If the solute both associates and dissociates in one of the solvents, the concentration of the solute becomes variable, violating the assumptions of the Nernst distribution law even more. Thus, this condition also renders the law inapplicable.

Evaluate option (d): none of the above

Since options (a), (b), and (c) are all conditions where Nernst distribution law is not applicable, 'none of the above' will not be a suitable answer for this question.

Key concepts

Solute association

In the realm of chemistry, solute association refers to the scenario where solute molecules come together to form larger aggregates when dissolved in a solvent. This phenomenon is quite significant as it changes the effective concentration of the solute in that solvent. Imagine it as tiny particles grouping together into bigger clusters.
When solute association occurs, the number of free solute particles decreases. This means the concentration of individual solute particles is lower than originally calculated.
It's essential to understand that the Nernst distribution law, represented by the equation \(K_{D}=C_{1} / C_{2}\), is built on the assumption that the solute's concentration remains the same while partitioning between two solvents. If association happens, this assumption is violated, making the law inapplicable. Here are some key points:

• Association can change the physical properties of the solution.
• This process can be temperature or concentration-dependent.

Understanding solute association helps in predicting solute behavior in reactions and partitioning, which is crucial in further chemical analyses.

Solute dissociation

Solute dissociation is the breaking apart of a solute molecule in a solvent into smaller molecules or ions. Unlike solute association, which decreases the number of solute molecules, dissociation increases the number of entities in the solution.
This process is commonly seen with ionic compounds, where they split into their respective ions when dissolved. This can be thought of as a molecule breaking up into pieces. For example, table salt (NaCl) dissociates into \(Na^+\) and \(Cl^-\) ions in water.
When considering the Nernst distribution law, the increase in solute entities due to dissociation alters the concentration of the solute. This impact defies the assumption that solute concentration remains constant between solvents. Thus, Nernst distribution law cannot be applied when dissociation occurs in either solvent. Key aspects include:

• Dissociation may depend on factors like solvent type and temperature.
• It affects the distribution and physical behavior of solutes in solvents.

Knowing about solute dissociation is vital for applications such as predicting a solute's stability and reactivity in different environments.

Distribution constant

The distribution constant, also known as the partition coefficient, is a ratio that describes how a solute distributes itself between two immiscible solvents. Defined by \(K_{D} = C_{1} / C_{2}\), it gives us insights into the relative solubility of a solute in these solvents.
You can think of it as a preference meter: if \(K_{D}\) is high, the solute is more soluble in solvent 1; if low, then in solvent 2. The distribution constant is a pivotal factor in processes such as purification and extraction.
To correctly apply the Nernst distribution law, the distribution constant assumes that solute concentration remains unchanged in either solvent. Factors that affect distribution constant include:

• The chemical nature of solute and solvents.
• The temperature of the system.

Understanding the concept of the distribution constant is indispensable for accurately predicting how substances partition, enabling applications in industrial chemical processes and environmental science.