Problem 19 - Chemistry The Molecular Science

Question

Consider these four solutions: $$ \begin{array}{lcc} \hline \text { Solution } & {\left[\mathrm{H}_{3} \mathrm{O}^{+}\right](\mathrm{M})} & {\left[\mathrm{OH}^{-}\right](\mathrm{M})} \\ \hline \mathrm{D} & 2 \times 10^{-3} & \\ \mathrm{E} & & 2 \times 10^{-7} \\ \mathrm{~F} & 4 \times 10^{-5} & \\ \mathrm{G} & & 5 \times 10^{-11} \\ \hline \end{array} $$ (a) Which solution has the highest \(\mathrm{H}_{3} \mathrm{O}^{+}\) concentration? (b) Which solution has the highest \(\mathrm{OH}^{-}\) concentration? (c) Which solution is closest to being a neutral solution?

Step-by-Step Solution

Answer

(a) Solution D; (b) Solution E; (c) Solution G.

Step 1: Identify Highest Hydronium Concentration

Examine the given solutions D, E, F, and G to identify the available \([\mathrm{H}_3\mathrm{O}^+]\) concentrations. D has \(2 \times 10^{-3} \ M\) and F has \(4 \times 10^{-5} \ M\). Solution D has the highest \([\mathrm{H}_3\mathrm{O}^+]\) concentration because \(2 \times 10^{-3} > 4 \times 10^{-5}\).

Step 2: Identify Highest Hydroxide Concentration

Check the given solutions for \([\mathrm{OH}^-]\) concentrations: solution E has \(2 \times 10^{-7} \ M\) and solution G has \(5 \times 10^{-11} \ M\). Solution E has the highest \([\mathrm{OH}^-]\) concentration because \(2 \times 10^{-7} > 5 \times 10^{-11}\).

Step 3: Determine Neutral Solution

A neutral solution has \([\mathrm{H}_3\mathrm{O}^+] \approx [\mathrm{OH}^-]\), approximately \(1 \times 10^{-7} \ M\). Check \([\mathrm{H}_3\mathrm{O}^+]\) in D and F and \([\mathrm{OH}^-]\) in E and G: Solution G, with \([\mathrm{OH}^-]\) of \(5 \times 10^{-11} \ M\), is closest to this point considering the typical value in neutral water and comparison with its available counterpart.

Key Concepts

Hydronium Concentration

Hydronium ions, denoted as \( ext{H}_3 ext{O}^+\), play a crucial role in determining the acidity of a solution. These ions form when a hydrogen ion \( (\text{H}^+) \) combines with a water molecule \( (\text{H}_2 ext{O}) \). The strength of an acid is often represented by the concentration of hydronium ions.
In the exercise, we analyzed various solutions to determine which had the highest hydronium concentration. Solution D stood out with a concentration of \(2 \times 10^{-3} \text{ M}\). Imagine hydronium concentration as the key to unlocking acidity – the higher the concentration, the more acidic the solution.
When comparing solutions, always consider:

• Larger \([ ext{H}_3 ext{O}^+]\) values indicate stronger acidity.
• Hydronium concentrations are expressed in molarity (\(\text{M}\), moles per liter).

By understanding these concepts, you'll get a better grasp of how acids behave and interact with other substances.

Hydroxide Concentration

Hydroxide ions \((\text{OH}^-)\) are pivotal in defining the basicity of a solution. These ions exist as lone pairs on oxygen and contribute to the solution's overall alkalinity.
Let's think about solutions E and G. From our analysis, we noticed that Solution E had the highest concentration of hydroxide ions at \(2 \times 10^{-7} \text{ M}\). This means Solution E is slightly more basic compared to other solutions, due to its higher \([ ext{OH}^-]\) concentration.
Important factors to remember include:

• A higher \([ ext{OH}^-]\) concentration indicates a more basic (or alkaline) solution.
• Like hydronium, hydroxide concentrations are measured in molarity.

Knowledge of hydroxide ion concentration helps in understanding the nature of basic solutions, which is fundamental in studying reactions, titrations, and pH balance.

Neutral Solution

Neutral solutions maintain a delicate balance between hydronium and hydroxide ions. In pure water, both concentrations are ideally \(1 \times 10^{-7} \text{ M}\), reflecting equilibrium.
In the exercise, determining a neutral solution means finding one where \([ ext{H}_3 ext{O}^+]\) and \([ ext{OH}^-]\) are equal or very close to this balance. From the given options, Solution G is closest to being neutral, as its \([ ext{OH}^-]\) concentration is nearest to the typical neutral point.
Consider these key points:

• Neutrality in solutions implies a balance, neither acidic nor basic.
• Factors like temperature can slightly shift the \(1 \times 10^{-7} \text{ M}\) benchmark in real-world conditions.

Understanding what constitutes a neutral solution aids in gauging solution stability, biochemical processes, and the pH scale's midpoint.