Problem 101 - Chemistry: An Atoms-Focused Approach

Question

Which of these solutions is the most acidic? Which is the most basic? i. \(1.0 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{3}\) ii. \(0.10 M \mathrm{H}_{2} \mathrm{SO}_{4}\) iii. \(0.30 M \mathrm{NaHSO}_{4}\) iv. \(0.30 M \mathrm{Na}_{2} \mathrm{SO}_{4}\) v. \(0.30 M \mathrm{Na}_{2} \mathrm{SO}_{3}\)

Step-by-Step Solution

Answer

Answer: The most acidic solution is \(1.0 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{3}\), and the most basic solution is \(0.30 M \mathrm{Na}_{2} \mathrm{SO}_{3}\).

Step 1: Identify the acidic or basic nature of each solution

We need to identify whether the solutions are acidic or basic. i. \(1.0 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{3}\): This solution contains \(\mathrm{H}_{2} \mathrm{SO}_{3}\) which forms \(\mathrm{H}^{+}\) ions and \(\mathrm{HSO}_{3}^{-}\) ions in water making it acidic. ii. \(0.10 M \mathrm{H}_{2} \mathrm{SO}_{4}\): The solution contains \(\mathrm{H}_{2} \mathrm{SO}_{4}\), a strong acid that dissociates completely into \(\mathrm{H}^{+}\) and \(\mathrm{HSO}_{4}^{-}\) ions, making it acidic. iii. \(0.30 M \mathrm{NaHSO}_{4}\): This solution contains \(\mathrm{NaHSO}_{4}\), which releases \(\mathrm{HSO}_{4}^{-}\) ions. The \(\mathrm{HSO}_{4}^-\) ion can disassociate into \(\mathrm{SO}_{4}^{2-}\) and \(\mathrm{H^{+}}\) ions, making this solution acidic. iv. \(0.30 M \mathrm{Na}_{2} \mathrm{SO}_{4}\): This solution contains \(\mathrm{Na}_{2} \mathrm{SO}_{4}\), which releases \(\mathrm{SO}_{4}^{2-}\) and \(\mathrm{Na}^{+}\) ions. As both ions are conjugates of a strong acid and a strong base, they don't affect the pH, and the solution is neutral. v. \(0.30 M \mathrm{Na}_{2} \mathrm{SO}_{3}\): This solution contains \(\mathrm{SO}_{3}^{2-}\) ions, which can react with water to form \(\mathrm{SO}_{3}^{-}\) and \(\mathrm{OH^{-}}\). This makes the solution basic.

Step 2: Understand relative strength based on concentration

Now we have the following information: i. \(1.0 \mathrm{M}\) \(\mathrm{H}_{2} \mathrm{SO}_{3}\): acidic ii. \(0.10 M\) \(\mathrm{H}_{2} \mathrm{SO}_{4}\): acidic iii. \(0.30 M\) \(\mathrm{NaHSO}_{4}\): acidic iv. \(0.30 M\) \(\mathrm{Na}_{2} \mathrm{SO}_{4}\): neutral v. \(0.30 M\) \(\mathrm{Na}_{2} \mathrm{SO}_{3}\): basic The relative strength of the acidic/basic nature of the given solutions can be estimated based on the ion concentration and their dissociation in water.

Step 3: Determine the most acidic and most basic solutions

Based on the concentration and the nature of ions, we can determine that: - The most acidic solution is \(1.0 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{3}\) due to the highest concentration of H+ ions. - The most basic solution is \(0.30 M \mathrm{Na}_{2} \mathrm{SO}_{3}\), as it is the only basic solution among the options given.

Key Concepts

Solutions

In the realm of chemistry, a solution is a homogeneous mixture consisting of two or more substances. A solution comprises a solute, which is the substance being dissolved, and a solvent, the substance in which the solute is dissolved. In most cases, water acts as the solvent in aqueous solutions. For example, when sodium sulfate (\( \mathrm{Na}_2 \mathrm{SO}_4 \)) dissolves in water, it breaks apart into its constituent ions, \( \mathrm{Na}^+ \) and \( \mathrm{SO}_4^{2-} \).
Understanding the properties of solutions helps us comprehend how different solutes, like various acids or bases, interact when they mix with a solvent like water. When dealing with acid-base reactions in solutions, it's crucial to consider both the concentration and the nature of the solute, as these characteristics determine the solution's behavior, such as its pH.

pH

The pH is a numerical scale used to specify the acidity or basicity of an aqueous solution. The pH scale typically ranges from 0 to 14, where pH values below 7 denote acidic solutions, values above 7 denote basic solutions, and a pH of 7 is neutral.

• An acidic solution, such as hydrochloric acid (\( \mathrm{HCl} \)), has a high concentration of hydrogen ions (\( \mathrm{H}^+ \)).
• A basic solution, like sodium hydroxide (\( \mathrm{NaOH} \)), contains higher concentrations of hydroxide ions (\( \mathrm{OH}^- \)).
• A neutral solution, such as pure water, has equal concentrations of \( \mathrm{H}^+ \) and \( \mathrm{OH}^- \).

To determine the most acidic or basic solution, comparing the concentrations of \( \mathrm{H}^+ \) or \( \mathrm{OH}^- \) ions is important. For example, in the given problem, the solution with the highest concentration of \( \mathrm{H}^+ \) ions, \( 1.0 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{3} \), has the lowest pH, making it the most acidic.

Dissociation

Dissociation in chemistry refers to the process by which molecules or ionic compounds split into smaller particles, usually ions, in a solution. This process occurs when an acid or base dissolves in water, forming ions.

• Strong acids like sulfuric acid (\( \mathrm{H_2SO_4} \)) dissociate fully, producing ample \( \mathrm{H}^+ \) ions.
• Weak acids, such as sulfurous acid (\( \mathrm{H_2SO_3} \)), dissociate partially, yielding fewer \( \mathrm{H}^+ \) ions.
• For substances like \( \mathrm{NaHSO_4} \), dissociation results in the release of \( \mathrm{HSO_4}^- \) ions, which can further dissociate slightly, contributing to the acidity of the solution.

The degree of dissociation impacts the number of ions present in the solution, influencing its pH. Solutions in which high dissociation occurs, particularly acids and bases, will often exhibit more significant changes in pH.

Acid Strength

The strength of an acid is determined by its ability to donate \( \mathrm{H}^+ \) ions to a solution. This ability is characterized as being either strong or weak.

• Strong acids: These acids, such as sulfuric acid (\( \mathrm{H_2SO_4} \)), dissociate completely in water. They release a high concentration of \( \mathrm{H}^+ \) ions, which increases the acidity, lowering the pH significantly.


• Weak acids: These acids, like sulfurous acid (\( \mathrm{H_2SO_3} \)), only partially dissociate in solution. They produce fewer \( \mathrm{H}^+ \) ions and thus are not as acidic as stronger acids.

determining the most acidic solution, the concentration of hydrogen ions is crucial. For example, the strong acid \( 0.10 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4} \) solutions have more \( \mathrm{H}^+ \) ions than weak acids at similar concentrations, but a highly concentrated weak acid like \( 1.0 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{3} \) can be more acidic due to its higher concentration, providing more \( \mathrm{H}^+ \) ions overall. This indicates that both concentration and acid strength are essential in evaluating the acidity.