Question

Indicate whether aqueous solutions of each of the following will contain only ions, only molecules, or mostly molecules and a few ions: a. acetic acid \(\left(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)\), a weak electrolyte b. NaBr, a strong electrolyte c. fructose \(\left(\mathrm{C}_{6} \mathrm{H}_{1}{ }_{2} \mathrm{O}_{6}\right)\), a nonelectrolyte

Short answer

a. Mostly molecules and a few ions, b. Only ions, c. Only molecules

Step-by-step solution

Identify the type of compound

Determine whether the given compound is a weak electrolyte, strong electrolyte, or nonelectrolyte.

Acetic Acid \(\text{(HC}_2 \text{H}_3 \text{O}_2)\)

Acetic acid is a weak electrolyte. It does not fully dissociate in water. Therefore, an aqueous solution of acetic acid will contain mostly molecules and a few ions.

Sodium Bromide (NaBr)

Sodium bromide is a strong electrolyte. It fully dissociates in water into \(\text{Na}^+\) and \(\text{Br}^-\) ions. Therefore, an aqueous solution of NaBr will contain only ions.

Fructose \(\text{(C}_6 \text{H}_{12} \text{O}_6)\)

Fructose is a nonelectrolyte. It does not dissociate into ions in water. Therefore, an aqueous solution of fructose will contain only molecules.

Summarize the findings

Summarize the findings for each substance, indicating whether the solution contains only ions, only molecules, or mostly molecules and a few ions.

Key concepts

Weak Electrolyte

Weak electrolytes are substances that do not completely dissociate into ions when dissolved in water. They only partially ionize, meaning a small fraction of the molecules will split into ions while the majority remain intact. For example, acetic acid \(\text{(HC}_2 \text{H}_3 \text{O}_2)\) is a common weak electrolyte. When acetic acid dissolves in water, only a few ions (\(\text{H}^+\) and \(\text{C}_2 \text{H}_3 \text{O}_2^-\)) are present in the solution, leaving most of the acetic acid molecules undissociated. So, in an aqueous solution of a weak electrolyte, you'll find mostly molecules and a few ions.

Strong Electrolyte

Strong electrolytes are substances that completely dissociate into ions when dissolved in water. This means that there are no intact molecules left in the solution, only ions. An example of a strong electrolyte is sodium bromide \(\text{NaBr}\). When sodium bromide dissolves in water, it separates fully into sodium ions (\(\text{Na}^+\)) and bromide ions \(\text{Br}^-\). Thus, an aqueous solution of a strong electrolyte will contain only ions. These ions conduct electricity very efficiently, which is why strong electrolytes are commonly used in electrical applications.

Nonelectrolyte

Nonelectrolytes are substances that do not dissociate into ions at all when dissolved in water. They exist in the solution solely as intact molecules, with no ion formation occurring. An example of a nonelectrolyte is fructose \(\text{(C}_6 \text{H}_{12} \text{O}_6)\). When fructose is added to water, it simply dissolves without forming any ions. Therefore, an aqueous solution of a nonelectrolyte will contain only molecules. Nonelectrolytes do not conduct electricity because there are no free ions to carry a charge.

Ion Dissociation

Ion dissociation refers to the process by which an ionic compound separates into its individual ions when dissolved in water. This process is essential in determining whether a substance is a strong electrolyte, weak electrolyte, or nonelectrolyte. For instance, when a strong electrolyte like sodium bromide \(\text{NaBr}\) dissolves in water, it dissociates completely into \(\text{Na}^+\) and \(\text{Br}^-\). In contrast, a weak electrolyte like acetic acid partially dissociates, resulting in fewer \(\text{H}^+\) and \(\text{C}_2 \text{H}_3 \text{O}_2^-\) ions. Nonelectrolytes, such as fructose \(\text{(C}_6 \text{H}_{12} \text{O}_6)\), do not undergo ion dissociation at all, remaining in molecular form.

Molecular Solutions

Molecular solutions consist of molecules that have dissolved in a solvent like water without breaking into ions. This is characteristic of nonelectrolytes such as fructose \(\text{(C}_6 \text{H}_{12} \text{O}_6)\). In such solutions, the molecules interact with the solvent purely through physical processes such as dissolution and solvation but remain intact. The absence of ions in molecular solutions means they do not conduct electricity, distinguishing them from ionic solutions that result from strong and weak electrolytes. Understanding the differences between molecular and ionic solutions is crucial for predicting the conductivity and behavior of substances in aqueous environments.