Problem 17 - Chemistry: The Central Science

Question

Specify what ions are present in solution upon dissolving each of the following substances in water: (a) \(\mathrm{FeCl}_{2}\), (b) \(\mathrm{HNO}_{3}\), (c) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\), (d) \(\mathrm{Ca}(\mathrm{OH})_{2}\).

Step-by-Step Solution

Answer

When each substance dissolves in water, the following ions are present in the solution: (a) \(\mathrm{FeCl}_{2}\): 1 \(\mathrm{Fe}^{2+}\) and 2 \(\mathrm{Cl}^{-}\) ions. (b) \(\mathrm{HNO}_{3}\): 1 \(\mathrm{H}^{+}\) and 1 \(\mathrm{NO}_{3}^{-}\) ions. (c) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\): 2 \(\mathrm{NH}_{4}^{+}\) and 1 \(\mathrm{SO}_{4}^{2-}\) ions. (d) \(\mathrm{Ca}(\mathrm{OH})_{2}\): 1 \(\mathrm{Ca}^{2+}\) and 2 \(\mathrm{OH}^{-}\) ions.

Step 1: (a) Identify ions for \(\mathrm{FeCl}_{2}\)

When \(\mathrm{FeCl}_{2}\) dissolves in water, it dissociates into its ions. The ions are: 1. Iron(II) ion: \(\mathrm{Fe}^{2+}\) 2. Chloride ion: \(\mathrm{Cl}^{-}\) Since there are two chloride ions in the formula, we have: 1 \(\mathrm{Fe}^{2+}\) and 2 \(\mathrm{Cl}^{-}\) ions in the solution.

Step 2: (b) Identify ions for \(\mathrm{HNO}_{3}\)

When \(\mathrm{HNO}_{3}\) dissolves in water, it dissociates into its ions. The ions are: 1. Hydrogen ion: \(\mathrm{H}^{+}\) 2. Nitrate ion: \(\mathrm{NO}_{3}^{-}\) So we have 1 \(\mathrm{H}^{+}\) and 1 \(\mathrm{NO}_{3}^{-}\) ions in the solution.

Step 3: (c) Identify ions for \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\)

When \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\) dissolves in water, it dissociates into its ions. The ions are: 1. Ammonium ion: \(\mathrm{NH}_{4}^{+}\) 2. Sulfate ion: \(\mathrm{SO}_{4}^{2-}\) Since there are two ammonium ions in the formula, we have: 2 \(\mathrm{NH}_{4}^{+}\) and 1 \(\mathrm{SO}_{4}^{2-}\) ions in the solution.

Step 4: (d) Identify ions for \(\mathrm{Ca}(\mathrm{OH})_{2}\)

When \(\mathrm{Ca}(\mathrm{OH})_{2}\) dissolves in water, it dissociates into its ions. The ions are: 1. Calcium ion: \(\mathrm{Ca}^{2+}\) 2. Hydroxide ion: \(\mathrm{OH}^{-}\) Since there are two hydroxide ions in the formula, we have: 1 \(\mathrm{Ca}^{2+}\) and 2 \(\mathrm{OH}^{-}\) ions in the solution.

Key Concepts

Chemical Compound Dissolution

Chemical compound dissolution refers to the process where a solid, liquid, or gas solute becomes incorporated into a liquid solvent, typically water, forming a solution. When a chemical compound dissolves in water, it breaks down into its constituent ions in a process called dissociation. Dissolution is driven by the interaction between the solvent molecules and the solute particles, which can overcome the forces holding the solute together.

In the context of ionic compounds, dissolution involves separating the ions that form the compound's crystal lattice structure. For example, when \(\mathrm{FeCl}_{2}\) is dissolved in water, the compound dissociates into one iron(II) ion \(\mathrm{Fe}^{2+}\) and two chloride ions \(\mathrm{Cl}^{-}\).

Factors affecting dissolution include the nature of the solute and solvent, temperature, and pressure. A compound's solubility in water determines how well it can dissolve. Soluble compounds like \(\mathrm{HNO}_{3}\) dissociate completely in water, facilitating various chemical reactions.

Ion Identification

Ion identification is crucial in understanding how substances behave in aqueous solutions. Ions are charged atoms or molecules and can be either positive (cations) or negative (anions). When identifying ions formed during the dissolution of a compound, it's essential to know the chemical formula of the substance because it indicates the type and ratio of ions present in the solution.

For instance, in calcium hydroxide \(\mathrm{Ca(OH)}_{2}\), which will dissociate into one calcium ion \(\mathrm{Ca}^{2+}\) and two hydroxide ions \(\mathrm{OH}^{-}\). The identification process involves examining the compound's formula and determining the number of each type of ion.

Let's take another example, ammonium sulfate \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\). This compound dissociates into two ammonium ions \(\mathrm{NH}_{4}^{+}\) and one sulfate ion \(\mathrm{SO}_{4}^{2-}\). Understanding these individual ions helps predict the behavior of solutions and their possible interactions in chemical reactions.

Aqueous Solution Chemistry

Aqueous solution chemistry focuses on reactions and behaviors of substances when dissolved in water. It's fundamental in understanding how substances interact with one another when ions form in solutions. In aqueous solutions, ions are dispersed throughout, allowing them to react with one another frequently. This predictability forms the basis for many chemical reactions, including neutralization, precipitation, and redox reactions.

For example, when an acid like \(\mathrm{HNO}_{3}\) dissolves in water, it donates hydrogen ions \(\mathrm{H}^{+}\) to the solution, making it acidic. In contrast, bases like \(\mathrm{Ca(OH)}_{2}\) donate hydroxide ions \(\mathrm{OH}^{-}\), resulting in a basic solution.

The balance of ions in an aqueous solution determines its properties, such as pH value, electrical conductivity, and reactivity. Studying aqueous solution chemistry helps in fields ranging from biochemistry to environmental science, where the properties of water solutions are critically important.