Problem 21 - Chemistry and Chemical Reactivity

Question

The following compounds are water-soluble. What ions are produced by each compound in aqueous solution? (a) KOH (b) \(\mathrm{K}_{2} \mathrm{SO}_{4}\) (c) \(\mathrm{LiNO}_{3}\) (d) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\)

Step-by-Step Solution

Answer

(a) KOH: \( \text{K}^{+} \), \( \text{OH}^{-}\); (b) \(\mathrm{K}_{2} \mathrm{SO}_{4}\): \( \text{K}^{+}, \text{SO}_{4}^{2-} \); (c) \(\mathrm{LiNO}_{3}\): \( \text{Li}^{+}, \text{NO}_{3}^{-} \); (d) \((\mathrm{NH}_{4})_{2} \mathrm{SO}_{4}\): \( \text{NH}_{4}^{+}, \text{SO}_{4}^{2-} \).

Step 1: Dissolution of KOH

When potassium hydroxide (KOH) dissolves in water, it dissociates completely into its constituent ions. The chemical equation for this process is: \[ \text{KOH (s)} \rightarrow \text{K}^{+} (aq) + \text{OH}^{-} (aq) \] Therefore, the ions produced are \(\text{K}^{+}\) and \(\text{OH}^{-}\).

Step 2: Dissolution of \(\mathrm{K}_{2} \mathrm{SO}_{4}\)

Potassium sulfate \(\mathrm{K}_{2} \mathrm{SO}_{4}\) dissociates in water into two potassium ions and one sulfate ion. The chemical reaction is: \[ \mathrm{K}_{2} \mathrm{SO}_{4} (s) \rightarrow 2 \text{K}^{+} (aq) + \text{SO}_{4}^{2-} (aq) \] So, it produces two \(\text{K}^{+}\) ions and one \(\text{SO}_{4}^{2-}\) ion.

Step 3: Dissolution of \(\mathrm{LiNO}_{3}\)

Lithium nitrate \(\mathrm{LiNO}_{3}\) dissociates in water into lithium ions and nitrate ions. The dissociation equation is: \[ \mathrm{LiNO}_{3} (s) \rightarrow \text{Li}^{+} (aq) + \text{NO}_{3}^{-} (aq) \] Thus, the ions produced are \(\text{Li}^{+}\) and \(\text{NO}_{3}^{-}\).

Step 4: Dissolution of \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\)

Ammonium sulfate \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\) dissociates in water to produce two ammonium ions and one sulfate ion. The chemical dissociation process is: \[ \left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4} (s) \rightarrow 2 \text{NH}_{4}^{+} (aq) + \text{SO}_{4}^{2-} (aq) \] This produces two \(\text{NH}_{4}^{+}\) ions and one \(\text{SO}_{4}^{2-}\) ion.

Key Concepts

aqueous solution

An aqueous solution is a mixture where water acts as the solvent, dissolving other substances. The term "aqueous" comes from the Latin word for water, signifying that the compounds are dispersed or dissipated in water.
This process involves the ionic or molecular compounds breaking up as they enter the water, resulting in a homogeneous mixture.

• Water serves as a medium that allows for the dispersal of dissolved substances.
• Dissolved compounds can either completely dissolve, like ionic compounds, or partially, like some polar covalent molecules.

Understanding aqueous solutions is vital in chemical equations because they indicate the state of reactants or products when they are dissolved in water. This is essential for predicting the behavior of chemicals in reactions that occur in water-dominant environments, like biology or environmental systems.

water-soluble compounds

Water-soluble compounds have the ability to dissolve readily in water, forming a clear and uniform solution. These compounds dissociate into ions when mixed with water.
The ease of dissolution of a compound in water depends on its polarity and the nature of its chemical bonds.

• Ionic compounds, such as salts, dissolve by dissociating into their constituent ions.
• Polar covalent compounds can also dissolve but might not fully dissociate into ions.
• Nonpolar compounds usually do not dissolve well in water.

The characteristic of being water-soluble is crucial in many chemical processes, including reactions in biological systems and industrial applications.

chemical equations

Chemical equations are symbolic representations used to demonstrate the changes that occur during a chemical reaction.
They show the reactants, which start a reaction, and the products, which are the substances formed by that reaction.

• An important aspect is that they represent the law of conservation of mass; the amount of each element is the same on both sides of the equation.
• In aqueous solutions, equations frequently highlight the dissociation of ionic compounds into their ions.

For example, in the dissolution of potassium sulfate (\(\mathrm{K}_{2} \mathrm{SO}_{4}\)), the chemical equation was:
\[ \mathrm{K}_{2} \mathrm{SO}_{4} (s) \rightarrow 2 \text{K}^{+} (aq) + \text{SO}_{4}^{2-} (aq) \]
Such expression allows us to understand how compounds behave in solutions, particularly important for predicting reaction outcomes.

ion production

Ion production refers to the creation of charged particles when a compound dissolves in a solvent, such as water.
When dissolved in water, ionic compounds break into positively and negatively charged ions, usually through dissociation.

• Cations are positively charged ions, such as \(\text{K}^{+}\) or \(\text{Li}^{+}\).
• Anions are negatively charged ions, like \(\text{OH}^{-}\) or \(\text{SO}_{4}^{2-}\).

The number of each type of ion formed depends on the specific compound and its stoichiometry. For instance, \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\) produces not just one \(\text{NH}_{4}^{+}\) ion, but two for each molecule dissolved.
Key to many processes, understanding ion production is vital for fields ranging from medicine to environmental science, illustrating how compounds interact within systems.