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 solute particles 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 $0.2\mathrm{mol}$ of solute particles?

Short answer

(a) In aqueous solutions, the solute particles present for acetone are ${\mathrm{CH}}_3{\mathrm{COCH}}_3$ molecules, for hypochlorous acid are $\mathrm{HClO}$, ${\mathrm{H}}^{+}$, and ${\mathrm{ClO}}^{-}$, and for ammonium chloride are ${\mathrm{NH}}_4^{+}$ and ${\mathrm{Cl}}^{-}$. (b) Acetone contains $0.1\mathrm{mol}$ of solute particles, hypochlorous acid contains somewhere between $0.1$ and $0.2\mathrm{mol}$ of solute particles, and ammonium chloride contains $0.2\mathrm{mol}$ of solute particles.

Step-by-step solution

Identify the solute particles in aqueous solutions of each compound

For acetone, a nonelectrolyte, it does not ionize when dissolved in water. Therefore, the solute particles present are just the acetone molecules themselves: ${\mathrm{CH}}_3{\mathrm{COCH}}_3$. For hypochlorous acid, a weak electrolyte, it ionizes partially in water, forming ions: $\mathrm{HClO}$ dissociates into ${\mathrm{H}}^{+}$ and ${\mathrm{ClO}}^{-}$. However, not all the molecules are ionized, so both the intact $\mathrm{HClO}$ and the ions ${\mathrm{H}}^{+}$ and ${\mathrm{ClO}}^{-}$ are present. For ammonium chloride, a strong electrolyte, it completely ionizes in water: ${\mathrm{NH}}_4\mathrm{Cl}$ dissociates into ${\mathrm{NH}}_4^{+}$ and ${\mathrm{Cl}}^{-}$. Thus, the solute particles present are the ions ${\mathrm{NH}}_4^{+}$ and ${\mathrm{Cl}}^{-}$.

Determine the number of moles of solute particles in 0.1 mol of each compound's solution

For acetone, since there are no ions formed when it dissolves, we have exactly 0.1 mol of solute particles from the 0.1 mol of acetone molecules. For hypochlorous acid, since it ionizes partially, the number of moles of solute particles when dissolving 0.1 mol of $\mathrm{HClO}$ will be somewhere between 0.1 and 0.2 moles (the value depends on the degree of ionization). For ammonium chloride, as it completely ionizes, we have 0.1 mol of ${\mathrm{NH}}_4^{+}$ and 0.1 mol of ${\mathrm{Cl}}^{-}$ ions, making a total of 0.2 mol of solute particles. Now, we can match the number of moles of solute particles to their corresponding compounds.

Match the number of moles of solute particles to their corresponding compounds

From our previous analysis: - Acetone has 0.1 mol of solute particles, as it does not ionize. - Hypochlorous acid has between 0.1 and 0.2 mol of solute particles, as it is a weak electrolyte that partially ionizes. - Ammonium chloride has 0.2 mol of solute particles, as it is a strong electrolyte and completely ionizes.

Key concepts

Nonelectrolyte

When we discuss nonelectrolytes, we refer to substances like acetone, which do not dissociate into ions in an aqueous solution. Nonelectrolytes remain as intact molecules when they dissolve in water. Therefore, in a solution of a nonelectrolyte, the only particles present are the original molecules themselves.

Acetone (${\mathrm{CH}}_3{\mathrm{COCH}}_3$) is an excellent example to illustrate this concept. When you dissolve 0.1 mol of acetone in water, you will still have 0.1 mol of acetone molecules in the solution. This happens because nonelectrolytes, like acetone, do not break apart or form ions in the solution.

Key features of nonelectrolytes include:

• No formation of ions in solution.
• Electrical conductivity is absent since no charged particles are present.
• Solely comprised of whole molecules.

Understanding nonelectrolytes provides a baseline to contrast with other types of electrolyte behavior.

Weak Electrolyte

Weak electrolytes, such as hypochlorous acid ($\mathrm{HClO}$), ionize only partially in solution. This partial ionization leads to a mixture of ions and un-ionized molecules in the solution.

When 0.1 mol of hypochlorous acid is dissolved in water, it does not fully dissociate into ions. Instead, only a fraction of the original $\mathrm{HClO}$ molecules become ions, specifically ${\mathrm{H}}^{+}$ and ${\mathrm{ClO}}^{-}$.

Because of this partial ionization, the number of solute particles in the solution will lie somewhere between 0.1 and 0.2 mol, depending on the degree of ionization.

Key characteristics of weak electrolytes:

• Partial ionization in solution.
• Presence of both ions and un-ionized molecules.
• Moderate electrical conductivity due to the presence of some ions.

A weak electrolyte demonstrates how substances can behave between the extremes of non-ionizing nonelectrolytes and fully ionizing strong electrolytes.

Strong Electrolyte

Strong electrolytes are compounds that completely dissociate into ions when dissolved in water, leading to an entirely ionic solution. Ammonium chloride (${\mathrm{NH}}_4\mathrm{Cl}$) is a prime example of a strong electrolyte.

When you dissolve 0.1 mol of ammonium chloride in water, it fully dissociates into 0.1 mol of ${\mathrm{NH}}_4^{+}$ and 0.1 mol of ${\mathrm{Cl}}^{-}$. This causes the total molar concentration of solute particles in solution to rise to 0.2 mol.

In general, strong electrolytes are characterized by:

• Complete ionization in solution.
• High electrical conductivity because of the abundance of ions.
• Absence of the original compound's molecules in solution.

Strong electrolytes highlight the capacity of certain solutes to completely break into ions when mixed with water, contrasting them with weak electrolytes and nonelectrolytes.