Problem 20 - Chemistry: The Central Science in SI Units, Global Edition

Question

Acetone, \(\mathrm{CH}_{3} \mathrm{COCH}_{3},\) is a nonelectrolyte; hypochlorous acid, \(\mathrm{HClO},\) is a weak electrolyte; and ammonium chloride, \(\mathrm{NH}_{4} \mathrm{Cl}\), is a strong electrolyte. (a) What are the solutes present in aqueous solutions of each compound? (b) If \(0.1 \mathrm{~mol}\) of each compound is dissolved in solution, which one contains \(0.2 \mathrm{~mol}\) of solute particles, which contains \(0.1 \mathrm{~mol}\) of solute particles, and which contains somewhere between 0.1 and 0,2 mol of solute particles?

Step-by-Step Solution

Answer

In aqueous solutions, acetone (\(\mathrm{CH}_{3}\mathrm{COCH}_{3}\)) is a nonelectrolyte and remains as 0.1 mol of intact molecules. Hypochlorous acid (\(\mathrm{HClO}\)) is a weak electrolyte, partially dissociating into \(\mathrm{H}^{+}\) and \(\mathrm{ClO}^{-}\), resulting in between 0.1 and 0.2 mol of solute particles. Ammonium chloride (\(\mathrm{NH}_{4}\mathrm{Cl}\)) is a strong electrolyte and fully dissociates into \(\mathrm{NH}_{4}^{+}\) and \(\mathrm{Cl}^{-}\), yielding a total of 0.2 mol of solute particles.

Step 1: Identifying the solutes in the aqueous solutions of the compounds

To determine the solutes present in the aqueous solutions of the three compounds, we need to know their behavior as nonelectrolytes, weak electrolytes, or strong electrolytes. Acetone is a nonelectrolyte, meaning it does not dissociate into ions in an aqueous solution. Therefore, the solute present in this solution will be unchanged acetone molecules, \(\mathrm{CH}_{3}\mathrm{COCH}_{3}\). Hypochlorous acid is a weak electrolyte, meaning it partially dissociates into ions in an aqueous solution. The solute present in this solution will be a mixture of undissociated hypochlorous acid, \(\mathrm{HClO}\), and its dissociated ions, \(\mathrm{H}^{+}\) and \(\mathrm{ClO}^{-}\). Ammonium chloride is a strong electrolyte, meaning it fully dissociates into ions in an aqueous solution. The solute present in this solution will be its dissociated ions, \(\mathrm{NH}_{4}^{+}\) and \(\mathrm{Cl}^{-}\).

Step 2: Calculating the number of solute particles in 0.1 mol of each compound in aqueous solution

Now that we know the solutes present in each solution, we can find the number of solute particles in each. (a) For acetone: Since it does not dissociate, 0.1 mol of acetone in solution will contain 0.1 mol of solute particles. (b) For hypochlorous acid: Since it is a weak electrolyte and partially dissociates, 0.1 mol of the acid in solution will produce an amount of solute particles between 0.1 mol and 0.2 mol, depending on the degree of dissociation of the acid. (c) For ammonium chloride: Since it is a strong electrolyte and fully dissociates, 0.1 mol of the salt will produce 0.1 mol \(\mathrm{NH}_{4}^{+}\) ions and 0.1 mol \(\mathrm{Cl}^{-}\) ions. Together, these make up a total of 0.1 + 0.1 = 0.2 mol of solute particles in the solution.

Key Concepts

Nonelectrolyte

Acetone exemplifies a nonelectrolyte, a type of compound that does not dissociate into ions in solution. Instead, when acetone is dissolved in water, the molecules remain intact without forming any charged particles. Because of this characteristic, nonelectrolytes do not conduct electricity through their solutions. Nonelectrolytes include many organic compounds, such as sugars and substances like acetone.

In practical terms, if you place 0.1 mol of acetone in water, you will still have 0.1 mol of solute particles, all of which are whole acetone molecules. This is because none of the acetone molecules separate into ions; they remain as neutral entities. Therefore, nonelectrolytes are important in studying solutions where the focus is on molecular interactions rather than ionic conductivity.

Weak Electrolyte

Hypochlorous acid ( \( \mathrm{HClO} \) ) serves as a classic example of a weak electrolyte. Weak electrolytes only partially dissociate into ions in solution. This means that when they dissolve, some of their molecules will split into ions, while others will remain as undissociated molecules.

For instance, with 0.1 mol of hypochlorous acid, the number of resultant solute particles will fluctuate between 0.1 and 0.2 mol based on how much it dissociates. This partial dissociation occurs due to dynamic equilibrium, a state where the formation of ions from the acid and the recombination of these ions back into ( \( \mathrm{HClO} \) ) balance each other.

Weak electrolytes are significant in chemical reactions and biological systems where the concentration of ions influences processes. They usually conduct electricity weakly, given the relatively low concentration of charged particles.

Strong Electrolyte

Ammonium chloride illustrates a strong electrolyte, a variety of compound that completely dissociates into ions when dissolved in water. This complete ionization leads to a solution enriched with charge carriers, enabling strong electrolytes to conduct electricity efficiently.

In the case of ammonium chloride, dissolving 0.1 mol in water results in 0.1 mol of \( \mathrm{NH}_4^+ \) ions and 0.1 mol of \( \mathrm{Cl}^- \) ions, totaling 0.2 mol of ions in the solution. This total of 0.2 mol of particles is because each molecule of ammonium chloride dissociates fully into its constituent ions.

Recognizing strong electrolytes is crucial for applications requiring significant electrical conduction, such as batteries and electrolysis processes. They are typically composed of ionic compounds like salts or strong acids and bases that readily provide a reliable source of ions in solution.