Question

Write the following salts in either the ionized or the nonionized form to best represent an aqueous solution: (a) \(\operatorname{AgF}(a q)\) (b) \(\operatorname{AgI}(s)\) (c) \(\mathrm{Hg}_{2} \mathrm{Cl}_{2}(\mathrm{~s})\) (d) \(\mathrm{NiCl}_{2}(a q)\)

Short answer

(a) AgF: ionized, (b) AgI: nonionized, (c) Hg2Cl2: nonionized, (d) NiCl2: ionized.

Step-by-step solution

Identify State and Solubility

First, determine if each compound is in aqueous ( (a q) ) or solid ( (s) ) form, as this will affect whether it is ionized in solution. Soluble aqueous compounds will dissociate into ions, whereas insoluble solids will not.

Assess Ionic Species for AgF(aq)

Since AgF is in aqueous form ( (aq) ), it is soluble in water and will dissociate into its ions. Therefore, in the solution, AgF will exist as Ag^+ and F^- ions.

Assess Ionic Species for AgI(s)

The compound AgI is a solid ( (s) ) and is poorly soluble in water. It will remain in its nonionized form as an insoluble solid and not dissociate appreciably into ions in an aqueous solution.

Assess Ionic Species for Hg2Cl2(s)

Hg_2Cl_2 is also a solid ( (s) ) and essentially insoluble in water. Like AgI , it remains nonionized in water and is not separated into its ions.

Assess Ionic Species for NiCl2(aq)

NiCl_2 is in aqueous form ( (aq) ), indicating it is soluble and will dissociate into its constituent ions in solution, Ni^{2+} and 2Cl^- .

Key concepts

Aqueous Solutions

An aqueous solution is a solution where water is the solvent. The term "aqueous" comes from "aqua," meaning water, and refers to substances that are dissolved in water. In chemistry, when a salt, for example, is labeled with \((aq)\), it means the substance is dissolved in water, making an aqueous solution.
When salts dissolve in water, the polar nature of water molecules interacts with the ionic compounds. This interaction allows the ions to be surrounded by water molecules, effectively separating them from each other. In simpler terms, the salt appears invisible because the ions are spread throughout the water.
Some advantages of using water as a solvent include:

• It is abundant and non-toxic.
• It has a high dielectric constant, which aids in dissolving ionic compounds.
• It maintains a stable liquid state over a wide range of temperatures.

By understanding aqueous solutions, we can predict how and if different substances will dissolve and ionize in water.

Solubility

Solubility refers to the ability of a substance to dissolve in a solvent, forming a homogeneous solution. If a salt like \(AgF (aq)\) or \(NiCl_2 (aq)\) is soluble in water, it means that it can dissolve completely, separating into ions to form an aqueous solution. On the other hand, substances like \(AgI (s)\) and \(Hg_2Cl_2 (s)\) are only slightly soluble or insoluble, meaning they do not dissolve well and remain largely in their solid form.
The solubility of a compound depends on several factors:

• The nature of the solvent and solute – "like dissolves like," meaning polar solutes tend to dissolve in polar solvents.
• Temperature – generally, more substances dissolve as the temperature increases.
• The presence of other substances in solution – certain ions can interfere with or enhance solubility.

Knowing the solubility of a compound can help determine whether it will exist in an ionized form in aqueous solutions or remain as a solid.

Dissociation of Ions

Dissociation is the process by which ionic compounds separate into individual ions when dissolving in water. This process is critical in aqueous solutions where ionic compounds dissociate to form a solution comprised of individual ions. For example, \(AgF (aq)\) dissociates into \(Ag^+\) and \(F^-\) ions, while \(NiCl_2 (aq)\) dissociates into \(Ni^{2+}\) and \(2Cl^-\) ions.
When discussing dissociation, it's essential to understand:

• Not all substances dissociate completely – some partially dissociate, known as weak electrolytes.
• Insoluble compounds like \(AgI (s)\) and \(Hg_2Cl_2 (s)\) do not readily dissociate.
• The degree of dissociation affects conductivity – more dissociated ions result in better electrical conductivity.

By recognizing how ionization occurs, we can better predict the behavior of ionic compounds in solutions, essential for many applications in chemistry and biology.