Calculate The Ph of Each of The Following Cases

Introduction to pH Calculation

The pH scale measures how acidic or basic a solution is. It ranges from 0 to 14, where:

• pH 0-6.9: Acidic solutions
• pH 7: Neutral solution (pure water)
• pH 7.1-14: Basic (alkaline) solutions

The pH scale is logarithmic, meaning each whole number change represents a tenfold difference in hydrogen ion concentration.

The pH Formula

For weak acids and bases, the pH can be calculated using the Henderson-Hasselbalch equation, which accounts for the dissociation constant (K_a) of the acid or base.

Calculating pH for Different Cases

Case 1: Strong Acid Solution

For a strong acid like hydrochloric acid (HCl), the pH can be directly calculated from the concentration of H⁺ ions.

Case 2: Weak Acid Solution

For weak acids, the pH depends on both the concentration of the acid and its dissociation constant (K_a).

Case 3: Buffer Solution

Buffer solutions resist changes in pH when small amounts of acid or base are added. The pH of a buffer can be calculated using the Henderson-Hasselbalch equation.

Case 4: Neutralization Reaction

When an acid and base react, the pH of the resulting solution depends on the stoichiometry of the reaction and the concentrations of the reactants.

Worked Examples

Example 1: Calculating pH of a Strong Acid Solution

Given a 0.1 M solution of HCl:

1. Determine the concentration of H⁺ ions: [H⁺] = 0.1 M
2. Apply the pH formula: pH = -log(0.1) = 1

The pH of the solution is 1, indicating a very acidic solution.

Example 2: Calculating pH of a Weak Acid Solution

For acetic acid (CH₃COOH) with a concentration of 0.1 M and a K_a of 1.8 × 10^-5:

1. Use the Henderson-Hasselbalch equation: pH = pK_a + log([A^-]/[HA])
2. Assume the solution is at equilibrium, so [A^-] ≈ [HA] = 0.1 M
3. Calculate pK_a: pK_a = -log(1.8 × 10^-5) ≈ 4.74
4. Apply the equation: pH = 4.74 + log(0.1/0.1) = 4.74

The pH of the acetic acid solution is approximately 4.74.