Calculate The Ph of A 0.350 M Hcn Solution

Introduction

The pH of a solution is a measure of its acidity or alkalinity. For a weak acid like hydrogen cyanide (HCN), the pH can be calculated using the dissociation constant (Kₐ) of the acid and its concentration.

Hydrogen cyanide is used in various industrial applications, including the production of acrylic fibers and plastics. Understanding its pH is important for safety and quality control in these processes.

pH Calculation Formula

The pH of a weak acid solution can be calculated using the following steps:

1. Determine the dissociation constant (Kₐ) of HCN. For hydrogen cyanide, Kₐ is approximately 4.9 × 10⁻¹⁰ at 25°C.
2. Calculate the concentration of hydronium ions (H₃O⁺) using the dissociation equation.
3. Convert the hydronium ion concentration to pH using the formula: pH = -log[H₃O⁺].

Where:

• Kₐ = dissociation constant of HCN (4.9 × 10⁻¹⁰)
• [HCN] = concentration of HCN in moles per liter (M)
• [H₃O⁺] = concentration of hydronium ions in moles per liter (M)

Worked Example

Let's calculate the pH of a 0.350 M HCN solution:

1. First, calculate the concentration of hydronium ions:
   [H₃O⁺] = √(4.9 × 10⁻¹⁰ × 0.350) ≈ √(1.715 × 10⁻¹⁰) ≈ 1.309 × 10⁻⁵ M
2. Next, calculate the pH:
   pH = -log₁₀ (1.309 × 10⁻⁵) ≈ 4.88

The pH of a 0.350 M HCN solution is approximately 4.88, indicating it is a moderately acidic solution.

Interpreting the Results

The pH scale ranges from 0 to 14, where:

• pH < 7: Acidic solution
• pH = 7: Neutral solution
• pH > 7: Basic solution

A pH of 4.88 means the solution is acidic, which is expected for a weak acid like HCN. The exact pH value can vary slightly depending on temperature and other factors.