Problem 20 - Chemistry The Central Science In Si Units

Question

Acetone, \(\mathrm{CH}_{3} \mathrm{COCH}_{3},\) is a nonelectrolyte; hypochlorous acid, 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 mol of each compound is dissolved in solution, which one contains 0.2 mol of solute particles, which contains 0.1 mol of solute particles, and which contains somewhere between 0.1 and 0.2 mol of solute particles?

Step-by-Step Solution

Answer

Acetone results in 0.1 mol of solute particles, ammonium chloride in 0.2 mol, and hypochlorous acid in between 0.1 and 0.2 mol.

Step 1: Understanding Solutes in Solution

When a nonelectrolyte like acetone, \(\text{CH}_3 \text{COCH}_3\), dissolves in water, it remains as whole molecules because it does not dissociate into ions. Therefore, the solute present is \(\text{CH}_3 \text{COCH}_3\) molecules only.When a strong electrolyte like ammonium chloride, \(\text{NH}_4\text{Cl}\), dissolves in water, it dissociates completely into its ions. Thus, the solutes present are \(\text{NH}_4^+\) and \(\text{Cl}^-\) ions.When a weak electrolyte like hypochlorous acid, \(\text{HClO}\), is dissolved, it partially dissociates into ions and partially remains as molecules. Therefore, both HClO molecules and its ions, \(\text{H}^+\) and \(\text{ClO}^-\), are present.

Step 2: Calculating Solute Particles for Nonelectrolyte

For the nonelectrolyte acetone, every mole of solute dissolved results in 1 mole of solute particles, as it remains as whole molecules. Therefore, dissolving 0.1 mol of acetone results in 0.1 mol of solute particles in solution.

Step 3: Calculating Solute Particles for Strong Electrolyte

For the strong electrolyte ammonium chloride, \(\text{NH}_4\text{Cl}\), each mole dissociates completely into \(\text{NH}_4^+\) and \(\text{Cl}^-\) ions, producing 2 moles of particles per mole of \(\text{NH}_4\text{Cl}\). Hence, dissolving 0.1 mol results in 0.2 mol of solute particles in solution.

Step 4: Calculating Solute Particles for Weak Electrolyte

For the weak electrolyte hypochlorous acid, \(\text{HClO}\), only a fraction of the 0.1 mol will dissociate into ions, while the rest remains as molecules. This results in a total between 0.1 mol and 0.2 mol of solute particles depending on the degree of ionization.

Key Concepts

Nonelectrolytes

Nonelectrolytes are fascinating substances that do not form ions when dissolved in water. This means they do not conduct electricity in their solution form. A great example of a nonelectrolyte is acetone, with the chemical formula \( ext{CH}_3 ext{COCH}_3\). When acetone is dissolved in water, it remains as intact molecules without breaking apart into ions. Consequently, in a solution, acetone contributes solely the original molecules.

• When you dissolve 0.1 mol of acetone in water, it yields exactly 0.1 mol of solute particles since no dissociation occurs.
• This characteristic of nonelectrolytes makes them unique among solutions as they do not alter the charge balance in the solution.

Nonelectrolytes are essential in many scientific processes where ion formation is undesirable, such as in certain chemical reactions and solvent properties.

Strong Electrolytes

Strong electrolytes are compounds that disassociate entirely when dissolved in water. This complete dissociation results in the solution being highly conductive to electricity. One example of a strong electrolyte is ammonium chloride, \( ext{NH}_4 ext{Cl}\). When it dissolves in water, it completely breaks into its respective ions: \( ext{NH}_4^+\) and \( ext{Cl}^-\).

• For every mole of ammonium chloride dissolved, there are 2 moles of ions generated.
• Thus, dissolving 0.1 mol of \( ext{NH}_4 ext{Cl}\) results in 0.2 mol of solute particles, accounting for the fully dissociated ions.

This makes strong electrolytes particularly important in applications like battery solutions and electrochemical processes, where high electrical conductivity is required.

Weak Electrolytes

Weak electrolytes only partially dissolve into ions in a solution. This partial dissociation means they do not conduct electricity as effectively as strong electrolytes. Hypochlorous acid, \( ext{HClO}\), is a classic example of a weak electrolyte. When it is dissolved in water, a portion of \( ext{HClO}\) molecules do dissociate into \( ext{H}^+\) and \( ext{ClO}^-\) ions, but many molecules remain intact.

• As a result, when 0.1 mol of \( ext{HClO}\) is dissolved in water, the solute particles will number somewhere between 0.1 mol and 0.2 mol depending on the extent of ionization.
• The degree of ionization can vary due to conditions such as concentration and temperature, influencing the proportion of molecules to ions in the solution.

Weak electrolytes are prevalent in biological systems and chemical equilibria, where partial ionization is often crucial for regulating processes.