Problem 25 - Chemistry An Atoms First Approach

Question

Show how each of the following strong electrolytes "breaks up" into its component ions upon dissolving in water by drawing molecular-level pictures. a. NaBr f. \(\mathrm{FeSO}_{4}\) b. \(\mathrm{MgCl}_{2}\) g. \(\mathrm{KMnO}_{4}\) c. \(\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}\) h. HCIO_ d. \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\) i. \(\mathrm{NH}_{4} \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\) (ammonium acetate) e. NaOH

Step-by-Step Solution

Answer

a. NaBr dissociates into Na+ (aq) and Br- (aq). f. \(\mathrm{FeSO}_{4}\) dissociates into Fe2+ (aq) and SO42- (aq). b. \(\mathrm{MgCl}_{2}\) dissociates into Mg2+ (aq) and 2 Cl- (aq). g. \(\mathrm{KMnO}_{4}\) dissociates into K+ (aq) and MnO4- (aq). c. \(\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}\) dissociates into Al3+ (aq) and 3 NO3- (aq). h. HCIO dissociates into H+ (aq) and ClO- (aq). d. \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\) dissociates into 2 NH4+ (aq) and SO42- (aq). i. \(\mathrm{NH}_{4} \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\) dissociates into NH4+ (aq) and C2H3O2- (aq). e. NaOH dissociates into Na+ (aq) and OH- (aq).

Step 1: Identify the ions

In the dissociation of NaBr upon dissolving in water, NaBr is dissociated into Na+ and Br- ions.

Step 2: Show Molecular-level pictures

Na+ (aq) + Br- (aq) f. \(\mathrm{FeSO}_{4}\)

Step 1: Identify the ions

In the dissociation of \(\mathrm{FeSO}_{4}\) upon dissolving in water, \(\mathrm{FeSO}_{4}\) is dissociated into Fe2+ and SO42- ions.

Step 2: Show Molecular-level pictures

Fe2+ (aq) + SO42- (aq) b. \(\mathrm{MgCl}_{2}\)

Step 1: Identify the ions

In the dissociation of \(\mathrm{MgCl}_{2}\) upon dissolving in water, \(\mathrm{MgCl}_{2}\) is dissociated into Mg2+ and 2 Cl- ions.

Step 2: Show Molecular-level pictures

Mg2+ (aq) + 2 Cl- (aq) g. \(\mathrm{KMnO}_{4}\)

Step 1: Identify the ions

In the dissociation of \(\mathrm{KMnO}_{4}\) upon dissolving in water, \(\mathrm{KMnO}_{4}\) is dissociated into K+ and MnO4- ions.

Step 2: Show Molecular-level pictures

K+ (aq) + MnO4- (aq) c. \(\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}\)

Step 1: Identify the ions

In the dissociation of \(\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}\) upon dissolving in water, \(\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}\) is dissociated into Al3+ and 3 NO3- ions.

Step 2: Show Molecular-level pictures

Al3+ (aq) + 3 NO3- (aq) h. HCIO

Step 1: Identify the ions

In the dissociation of HCIO upon dissolving in water, HCIO is dissociated into H+ and ClO- ions.

Step 2: Show Molecular-level pictures

H+ (aq) + ClO- (aq) d. \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\)

Step 1: Identify the ions

In the dissociation of \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\) upon dissolving in water, \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\) is dissociated into 2 NH4+ and SO42- ions.

Step 2: Show Molecular-level pictures

2 NH4+ (aq) + SO42- (aq) i. \(\mathrm{NH}_{4} \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\) (ammonium acetate)

Step 1: Identify the ions

In the dissociation of \(\mathrm{NH}_{4} \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\) upon dissolving in water, ammonium acetate is dissociated into NH4+ and C2H3O2- ions.

Step 2: Show Molecular-level pictures

NH4+ (aq) + C2H3O2- (aq) e. NaOH

Step 1: Identify the ions

In the dissociation of NaOH upon dissolving in water, NaOH is dissociated into Na+ and OH- ions.

Step 2: Show Molecular-level pictures

Na+ (aq) + OH- (aq)

Key Concepts

Ionic Compounds

Ionic compounds are substances composed of positive and negative ions. These ions are held together by strong electrostatic forces known as ionic bonds. Common examples include sodium bromide (NaBr), magnesium chloride (MgCl\(_2\)), and aluminum nitrate (Al(NO\(_3\))\(_3\)). Ionic compounds typically form between metals and nonmetals. For instance, NaBr is formed from sodium (a metal) and bromine (a nonmetal).

One of the critical properties of ionic compounds is their ability to dissolve in water. When ionic compounds dissolve, they break apart into their individual ions. This process is known as dissociation.

• Example: NaBr dissociates into Na\(^+\) and Br\(^-\)
• Example: MgCl\(_2\) dissociates into Mg\(^{2+}\) and two Cl\(^-\)

Understanding ionic compounds and their dissociation is vital for comprehending reactions in aqueous solutions and predicting the properties of the dissolved ions.

Aqueous Solutions

An aqueous solution is a solution in which water is the solvent. In such solutions, substances (solutes) dissolve in water, a process heavily influenced by the nature of the solute. For ionic compounds, their dissolution results in the separation of ions, leading to an "ionic atmosphere" within the solution. When NaBr, for instance, dissolves in water, it separates into Na\(^+\) and Br\(^-\) ions. This result is a solution where these ions are uniformly distributed throughout the water.

Water molecules play a crucial role in this process. Water is a polar molecule, having a partial positive charge on the hydrogen atoms and a partial negative charge on the oxygen atom. This polarity allows water to surround and separate the ions, stabilizing them in the solution. This action of water is often referred to as a solvation or hydration process.

• Water surrounds Na\(^+\) stabilizing it with its negative oxygen side.
• Likewise, Br\(^-\) ions are stabilized by the hydrogen side of water molecules.

This capability of water makes it an excellent medium for numerous chemical reactions.

Molecular-level Illustrations

Visualizing the dissociation of ionic compounds at the molecular level is crucial for understanding how these processes occur. These illustrations often show how ions from an ionic compound, such as NaBr or MgCl\(_2\), separate and spread out when dissolved in water. Each ion is depicted surrounded by water molecules highlighting the solvation process.

For example, a molecular-level illustration of NaBr dissolving would show:

• Na\(^+\) ion surrounded by the oxygen ends of water molecules.
• Br\(^-\) ion surrounded by the hydrogen ends of water molecules.

Such images help us understand not just the physical process of dissolution but also the energetic changes involved as bonds break and new interactions form. These molecular visualizations are foundational in chemistry education as they provide an intuitive grasp of the microscopic interactions happening in a solution. They reveal why substances like ionic solids have unique properties and how they transform when introduced to solvents like water.