Problem 102 - Chemistry and Chemical Reactivity

Question

Which has the larger concentration of hydronium ions, \(0.015 \mathrm{M} \mathrm{HCl}\) or aqueous \(\mathrm{HCl}\) with a \(\mathrm{pH}\) of \(1.20 ?\)

Step-by-Step Solution

Answer

HCl with a pH of 1.20 has a higher [H⁺].

Step 1: Understand the Problem

We need to compare the concentration of hydronium ions ([H⁺]) for two different solutions of HCl: a 0.015 M solution and another solution with a pH of 1.20.

Step 2: Determine [H⁺] from pH

The concentration of hydronium ions can be calculated using the pH of a solution. The formula is \([H^{+}] = 10^{- ext{pH}}\). Let’s calculate for HCl with a pH of 1.20.\[[H^{+}] = 10^{-1.20} = 0.0631 ext{ M}\]

Step 3: Compare Concentrations

Now, compare the [H⁺] concentrations from the two scenarios: - 0.015 M - 0.0631 M The concentration 0.0631 M from the pH 1.20 solution is greater than the 0.015 M solution.

Key Concepts

Understanding Hydronium Ions

Hydronium ions, commonly represented as \(\text{H}_3\text{O}^+\), play a crucial role in acid solutions.When an acid dissolves in water, it donates a proton (\(\text{H}^+\)) to a water molecule to form a hydronium ion. This chemical species is a reflection of the acidic nature of a solution and is frequently used to discuss the acidity levels in aqueous solutions.

• Hydronium ions result from the protonation of a water molecule.
• The concentration of hydronium ions in a solution indicates its acidity. Higher concentrations mean a more acidic solution.
• In dilute solutions, the concentration of hydronium ions is often used interchangeably with the concentration of hydrogen ions (\(\text{H}^+\)).

Understanding the concentration of hydronium ions is essential for pH calculations, as it directly impacts the pH value of a solution.This concentration informs us about the acidic strength and potential chemical reactivity of the solution.

The Process of pH Calculation

Calculating the pH of a solution is a fundamental concept in chemistry.It provides insights into the acidity or basicity (alkalinity) of a solution.The pH scale is logarithmic, ranging from 0 to 14, and is derived from the concentration of hydronium ions.
To calculate pH, we use the formula: \[pH = -\log_{10}[\text{H}_3\text{O}^+]\]This formula highlights the inverse relationship between hydronium ion concentration and pH.

• Low pH values (0-6.9) indicate a high concentration of hydronium ions, suggesting the solution is acidic.
• Neutral solutions have a pH of approximately 7, where hydronium and hydroxide ions are in equilibrium.
• High pH values (7.1-14) indicate a low concentration of hydronium ions, meaning the solution is basic.

It's important to understand that even small changes in pH reflect significant changes in hydronium ion concentrations due to the logarithmic nature of the scale.

Exploring Acid Solutions

Acid solutions are characterized by their ability to donate protons (hydrogen ions) and their low pH values.An acid like hydrochloric acid (HCl) dissociates in water to increase hydronium ion concentration.

• The strength of an acid depends on its degree of ionization in water.
• Strong acids completely ionize, leading to higher concentrations of hydronium ions.
• Weak acids partially ionize, resulting in lower concentrations of hydronium ions compared to strong acids of the same concentration.

When comparing acid solutions, one should note both the concentration of the acid (\(\text{M}\), meaning molarity) and its degree of ionization, both of which affect the hydronium ion concentration.For example, an acid solution of 0.015 M HCl is less acidic than one with a pH of 1.20, indicating fewer hydronium ions in the former, as shown in the original exercise solution.