Calculate Ph of 0.01 Nh4cl Solution

Introduction

When NH4Cl dissolves in water, it undergoes partial dissociation according to the following reaction:

The NH4+ ion can further react with water to form the weak base NH3 and hydronium ions:

This equilibrium allows us to calculate the pH of the solution using the Henderson-Hasselbalch equation.

Calculation Method

The pH of a solution containing NH4+ and NH3 can be calculated using the Henderson-Hasselbalch equation:

Where:

• pKa is the negative logarithm of the acid dissociation constant for NH4+ (-log(5.6 × 10-10))
• [NH3] is the concentration of NH3
• [NH4+] is the concentration of NH4+

For a 0.01 molar NH4Cl solution, we can assume that the concentration of NH4+ is equal to the initial concentration of NH4Cl (0.01 M) and that the concentration of NH3 is negligible initially.

Example Calculation

Let's calculate the pH of a 0.01 M NH4Cl solution:

1. Determine the pKa value for NH4+ (5.75)
2. Assume [NH4+] = 0.01 M and [NH3] ≈ 0 M
3. Apply the Henderson-Hasselbalch equation:
   pH = 5.75 + log(0/0.01) = 5.75 + log(0) = 5.75 - ∞ = -∞
4. This result indicates that the solution is highly acidic due to the complete dissociation of NH4Cl and the formation of H3O+ from NH4+.

Interpretation

The pH of a 0.01 M NH4Cl solution is typically around 4.75, indicating a moderately acidic solution. This is lower than pure water (pH 7) but not as acidic as strong mineral acids. The solution contains both NH4+ and NH3 in equilibrium, with NH4+ being the dominant species at this concentration.

This type of solution is commonly used in laboratory settings and industrial processes where a slightly acidic buffer is needed.