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Calculate Ph of A 0.4m Solutin of Nacooh with Ka

Reviewed by Calculator Editorial Team

This calculator determines the pH of a 0.4M solution of sodium acetate (NaCOOH) given its acid dissociation constant (Ka). The calculation follows standard acid-base chemistry principles.

Introduction

Sodium acetate (NaCOOH) is a weak acid that dissociates in water to form acetate ions (CH₃COO⁻) and hydrogen ions (H⁺). The pH of a solution depends on the concentration of these ions and the acid dissociation constant (Ka).

For a weak acid like NaCOOH, the pH can be calculated using the Henderson-Hasselbalch equation when the solution is buffered. However, for a dilute solution, we can use the Ka value directly.

Calculation Method

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

  1. Determine the concentration of the weak acid (C)
  2. Find the acid dissociation constant (Ka)
  3. Calculate the concentration of hydrogen ions ([H⁺]) using the equation:
    [H⁺] = √(Ka × C)
  4. Calculate the pH using the equation:
    pH = -log₁₀([H⁺])

Note: This calculation assumes the solution is dilute and that the weak acid is the only significant source of hydrogen ions.

Worked Example

Let's calculate the pH of a 0.4M solution of NaCOOH with a Ka of 1.8 × 10⁻⁵.

  1. Given: C = 0.4M, Ka = 1.8 × 10⁻⁵
  2. Calculate [H⁺]:
    [H⁺] = √(1.8 × 10⁻⁵ × 0.4) = √(7.2 × 10⁻⁵) ≈ 8.49 × 10⁻³ M
  3. Calculate pH:
    pH = -log₁₀(8.49 × 10⁻³) ≈ 2.07

The pH of this solution is approximately 2.07.

FAQ

What is the Ka value for NaCOOH?
The Ka value for sodium acetate (NaCOOH) is typically around 1.8 × 10⁻⁵ at 25°C. This value can vary slightly depending on temperature and other conditions.
How does concentration affect the pH?
For a weak acid, increasing the concentration increases the [H⁺] and thus decreases the pH. The relationship is not linear because it follows the square root relationship shown in the calculation.
Can this calculator be used for other weak acids?
Yes, the same calculation method applies to other weak acids as long as you know the Ka value and the concentration. The calculator can be adapted for other acids by changing the Ka value.
What if the solution is not dilute?
For concentrated solutions, the calculation becomes more complex and may require iterative methods or the use of the Henderson-Hasselbalch equation if a buffer system is present.