Calculate Ph of Ammonium Chloride 0.00142m

Introduction

Ammonium chloride (NH₄Cl) is a weak electrolyte that dissociates in water to form ammonium ions (NH₄⁺) and chloride ions (Cl⁻). The pH of an ammonium chloride solution can be calculated using the Henderson-Hasselbalch equation, which relates the pH of a buffer solution to the ratio of the concentrations of a weak acid and its conjugate base.

For ammonium chloride, the relevant acid-base pair is NH₄⁺/NH₃. The pKa of NH₄⁺ is approximately 9.25 at 25°C. The pH of the solution can be calculated using the formula:

Where:

• pKa is the acid dissociation constant of NH₄⁺ (9.25 at 25°C)
• [NH₃] is the concentration of ammonia (NH₃)
• [NH₄⁺] is the concentration of ammonium ions (NH₄⁺)

How to Calculate pH

To calculate the pH of an ammonium chloride solution:

1. Determine the concentration of ammonium chloride (M).
2. Assume complete dissociation of NH₄Cl to form NH₄⁺ and Cl⁻.
3. Calculate the concentration of NH₄⁺, which is equal to the concentration of NH₄Cl.
4. Calculate the concentration of NH₃ using the equilibrium constant for the reaction NH₄⁺ ⇌ NH₃ + H⁺.
5. Apply the Henderson-Hasselbalch equation to find the pH.

Ammonium Chloride pH

The pH of a 0.00142M ammonium chloride solution can be calculated as follows:

1. Given [NH₄Cl] = 0.00142 M, [NH₄⁺] = 0.00142 M.
2. The equilibrium constant for NH₄⁺ dissociation is K = 10^-9.25.
3. At equilibrium, [NH₃] = [NH₄⁺] × K = 0.00142 × 10^-9.25 ≈ 1.42 × 10^-13 M.
4. Apply the Henderson-Hasselbalch equation:

The calculated pH of a 0.00142M ammonium chloride solution is approximately 0.25.

Example Calculation

Let's calculate the pH of a 0.00142M ammonium chloride solution step-by-step:

1. Given [NH₄Cl] = 0.00142 M, [NH₄⁺] = 0.00142 M.
2. Using the equilibrium constant K = 10^-9.25, calculate [NH₃]:

[NH₃] = [NH₄⁺] × K = 0.00142 × 10^-9.25 ≈ 1.42 × 10^-13 M

3. Apply the Henderson-Hasselbalch equation:

pH = 9.25 + log₁₀([NH₃]/[NH₄⁺]) = 9.25 + log₁₀(1.42 × 10^-13/0.00142)

= 9.25 + log₁₀(1.0 × 10^-9)

= 9.25 - 9 ≈ 0.25

The pH of the solution is approximately 0.25, indicating a very acidic solution.