Question

The best conductor of electricity is a \(0.1 \mathrm{M}\) solution of (a) Boric acid (b) Sulphuric acid (c) Acetic acid (d) Propanoic acid

Short answer

Sulphuric acid (b) is the best conductor of electricity because it is a strong acid and dissociates completely in solution.

Step-by-step solution

Understanding the Concept of Electrical Conductivity

The electrical conductivity of a solution is determined by the presence of ions in it. Acids dissociate in water to produce H+ ions which conduct electricity. The stronger the acid, the more it dissociates, and the better it conducts electricity.

Analyzing the Given Acids

Boric acid is a weak acid and does not dissociate completely in solution. Sulphuric acid is a strong acid and dissociates completely in solution. Acetic acid is a weak acid and dissociates partially in solution. Propanoic acid is also a weak acid and dissociates partially in solution.

Deciding the Best Conductor

Sulphuric acid, being a strong acid, will dissociate completely in solution compared to the weak acids listed. Therefore, a solution of sulphuric acid will have more free H+ ions available to conduct electricity.

Key concepts

Acid Dissociation

When we talk about acid dissociation, it refers to the process of an acid breaking apart into ions when it's dissolved in water. This is an essential concept that affects a solution's electrical conductivity. For instance, when boric acid is dissolved in water, it will dissociate into hydrogen ions (H+) and anions, but only to a limited extent since it’s a weak acid. This partial dissociation results in fewer ions in the solution, which directly translates to lower electrical conductivity.

On the other hand, when considering strong acids like sulphuric acid, dissociation is almost complete, meaning that practically every molecule breaks apart to release H+ ions and anions. These ions are what carry electrical current through the solution. The dissociation process can be represented by a chemical equation, where the reactant (acid) arrow points to the products (ions). The extent of dissociation is a significant factor when evaluating the conductive capabilities of acid solutions.

Strong and Weak Acids

The terms 'strong' and 'weak' in acid context refer to an acid's propensity to dissociate in water. Strong acids, such as sulphuric acid, ionize completely, which means that each molecule of the acid separates into its constituent ions when dissolved in a solvent like water. This complete ionization leads to a high concentration of hydrogen ions (H+), making the solution a very good electrical conductor.

In contrast, weak acids like acetic acid and propanoic acid do not fully ionize; only a small fraction of their molecules dissociate to form H+ ions and their corresponding anions. Since the degree of dissociation is less, weak acids result in lower H+ ion concentration, and therefore, demonstrate less electrical conductivity compared to strong acids. Understanding this distinction is crucial for predicting and explaining the behavior of acids in solutions.

Ionic Conductivity

Ionic conductivity is the measure of a solution's ability to conduct electricity, which is dependent on the presence of free, charge-carrying ions. In an acidic solution, the H+ ions, alongside other anions, are the charge carriers. The more ions available in the solution, the higher the conductivity. This means that solutions formed from strong acids, which fully dissociate, will have more free ions and thus higher ionic conductivity.

However, it's not just about the number of ions but also their mobility. Factors that influence ionic mobility include the viscosity of the solution, the size of the ions, and the temperature. For instance, at higher temperatures, ions move more rapidly, which can increase conductivity. A solution’s ionic conductivity is key to understanding its efficacy in transmitting electrical current in practical applications like batteries and electroplating.

Molarity and Solution Concentration

Molarity, denoted by the unit 'M', is a measurement of the concentration of a solution, expressing the number of moles of solute dissolved in one liter of solution. When comparing the conductivity of various solutions, it is crucial to consider their molarities. A higher molarity indicates a higher number of solute particles, which upon dissociation, increase the number of ions available to conduct electricity.

In the context of the textbook exercise, all the acids were compared at the same molarity of 0.1 M. Despite the equal molarity, sulphuric acid provides the highest conductivity due to its full dissociation into ions. This concept helps explain why, despite similar concentrations, the conductive properties of acidic solutions can differ markedly, reflecting the importance of both the concentration of the solution and the nature of the acid dissolved in it.