In an acidic solution, how does the concentration of H₃O⁺ compare to the concentration of OH^-?

Verified step by step guidance

1. Understand that in any aqueous solution, the concentrations of H₃O⁺ (hydronium ions) and OH⁻ (hydroxide ions) are related by the ion-product constant for water, Kw, which is 1.0 × 10⁻¹⁴ at 25°C. This relationship is expressed as: $K_w=\; [H_{3}O+]\; \times \; [\mathrm{OH}-]$.
2. Recognize that an acidic solution is defined as one where the concentration of H₃O⁺ is greater than the concentration of OH⁻. This means: $[H_{3}O+]\; >\; [\mathrm{OH}-]$.
3. Recall that the pH of a solution is a measure of its acidity and is calculated using the formula: $\mathrm{pH}=\; -\log [H_{3}O+]$. For an acidic solution, the pH is less than 7.
4. Use the relationship between pH and pOH, which is given by: $\mathrm{pH}+\mathrm{pOH}=\; 14$. In an acidic solution, since the pH is less than 7, the pOH will be greater than 7, indicating a lower concentration of OH⁻.
5. Conclude that in an acidic solution, the concentration of H₃O⁺ is higher than the concentration of OH⁻, and this imbalance is what defines the solution as acidic.

Key Concepts

Acidic Solutions

An acidic solution is characterized by a higher concentration of hydronium ions (H₃O⁺) compared to hydroxide ions (OH⁻). This imbalance results in a pH value less than 7, indicating acidity. In such solutions, the presence of H₃O⁺ ions is what defines the solution as acidic, affecting various chemical reactions and properties.

pH Scale

The pH scale quantifies the acidity or basicity of a solution, ranging from 0 to 14. A pH less than 7 indicates an acidic solution, where the concentration of H₃O⁺ is greater than that of OH⁻. Each unit change in pH represents a tenfold change in H₃O⁺ concentration, making it a crucial tool for understanding the nature of solutions.

Ion Product of Water

The ion product of water (Kw) is the equilibrium constant for the self-ionization of water, defined as Kw = [H₃O⁺][OH⁻] = 1.0 x 10⁻¹⁴ at 25°C. In acidic solutions, as the concentration of H₃O⁺ increases, the concentration of OH⁻ must decrease to maintain this constant. This relationship is fundamental in determining the balance of ions in any aqueous solution.