Question

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

Short answer

Upon dissolving the given substances in water, the following ions are present in the solution: (a) \(\mathrm{Zn}^{2+}\) and \(\mathrm{Cl}^-\), (b) \(\mathrm{H}^{+}\) and \(\mathrm{NO}_{3}^-\), (c) \(\mathrm{NH}_{4}^+\) and \(\mathrm{SO}_{4}^{2-}\), and (d) \(\mathrm{Ca}^{2+}\) and \(\mathrm{OH}^-\).

Step-by-step solution

(a) Dissolving ZnCl2 in water

When \(\mathrm{ZnCl}_{2}\) is dissolved in water, it separates into its constituent ions: a zinc ion (\(\mathrm{Zn}^{2+}\)) and two chloride ions (\(2\times\mathrm{Cl}^-\)). Therefore, the ions present in the solution are \(\mathrm{Zn}^{2+}\) and \(\mathrm{Cl}^-\) ions.

(b) Dissolving HNO₃ in water

When \(\mathrm{HNO}_{3}\) is dissolved in water, it ionizes into hydrogen ions (\(\mathrm{H}^{+}\)) and nitrate ions (\(\mathrm{NO}_{3}^-\)). Therefore, the ions present in the solution are \(\mathrm{H}^{+}\) and \(\mathrm{NO}_{3}^-\) ions.

(c) Dissolving (NH₄)₂SO₄ in water

When \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\) is dissolved in water, it separates into its constituent ions: two ammonium ions (\(2\times\mathrm{NH}_{4}^+\)) and one sulfate ion (\(\mathrm{SO}_{4}^{2-}\)). Therefore, the ions present in the solution are \(\mathrm{NH}_{4}^+\) and \(\mathrm{SO}_{4}^{2-}\) ions.

(d) Dissolving Ca(OH)₂ in water

When \(\mathrm{Ca}(\mathrm{OH})_{2}\) is dissolved in water, it separates into its constituent ions: a calcium ion (\(\mathrm{Ca}^{2+}\)) and two hydroxide ions (\(2\times\mathrm{OH}^-\)). Therefore, the ions present in the solution are \(\mathrm{Ca}^{2+}\) and \(\mathrm{OH}^-\) ions.

Key concepts

Dissolution Process

The dissolution process involves the breaking apart of substances when they interact with a solvent, often water, to form a solution. In this context, let's focus on substances like

• Zinc chloride (\( \mathrm{ZnCl}_2 \))
• Nitric acid (\( \mathrm{HNO}_3 \))
• Ammonium sulfate (\( \left(\mathrm{NH}_4\right)_{2} \mathrm{SO}_4 \))
• Calcium hydroxide (\( \mathrm{Ca(OH)}_2 \))

As each of these substances interacts with water, they dissociate into individual ions. For instance, when zinc chloride dissolves in water, it separates into zinc ions and chloride ions. This process is crucial in determining the properties of the resulting solution, including its conductivity and reactivity.

Aqueous Solutions

An aqueous solution refers to a solution where water acts as the solvent. Water's unique ability to dissolve many substances makes it an excellent medium for chemical reactions. When substances like calcium hydroxide or nitric acid are dissolved in water, they form aqueous solutions. The ions within these solutions are surrounded by water molecules, a phenomenon known as hydration. This helps stabilize the ions and allows them to move freely, making the solution conductive. The dissolution of substances into ions is essential for many biological and chemical processes, including nutrient absorption and chemical synthesis.

Chemical Ionization

Chemical ionization occurs during the dissolution process when a molecule separates into its constituent ions. This can happen either through dissociation, as with zinc chloride, or through ionization, as with nitric acid. For example, when ammonium sulfate dissolves in water, it dissociates into ammonium ions and sulfate ions. Factors affecting ionization include:

• Temperature: Increasing temperature usually increases ionization.
• Concentration: The concentration of the dissolved substance can influence the extent of ionization.
• Nature of the solvent: Water, being polar, is excellent at promoting ionization.

Understanding ionization is key to predicting how substances will behave in different chemical environments.

Inorganic Chemistry

Inorganic chemistry is the branch of chemistry dealing with inorganic compounds, often those without carbon-hydrogen bonds. This includes a diverse set of substances, such as salts like zinc chloride and acids like nitric acid. In inorganic chemistry, understanding the behavior of ions in solutions is crucial. - **Ions and Reactions:** Ions are the active participants in many reactions, forming products through recombination. - **Acids and Bases:** Many inorganic reactions involve acids or bases dissolving, followed by ionization. For instance, calcium hydroxide provides hydroxide ions, which can neutralize acids. The study of these ion interactions is foundational to discovering new compounds and reactions, making inorganic chemistry an essential field of study.