1. What is the Sodium Phosphate pH Formula?

The sodium phosphate pH formula calculates the approximate pH of a trisodium phosphate solution based on its dissociation constants. For Na₃PO₄, the pH is approximately the average of the second and third pKa values due to hydrolysis to the intermediate form.

2. How Does the Calculator Work?

The calculator uses the sodium phosphate pH formula:

Where:

• \( pKa_2 \) — Second dissociation constant of phosphoric acid
• \( pKa_3 \) — Third dissociation constant of phosphoric acid

Explanation: This formula provides an approximation of the pH for trisodium phosphate solutions, which hydrolyze to form the intermediate species HPO₄²⁻.

3. Importance of pH Calculation for Sodium Phosphate

Details: Accurate pH estimation is crucial for buffer preparation, biochemical applications, and industrial processes where sodium phosphate is used as a pH regulator or cleaning agent.

4. Using the Calculator

Tips: Enter the pKa₂ and pKa₃ values for phosphoric acid. Typical values are pKa₂ ≈ 7.20 and pKa₃ ≈ 12.67, but these may vary slightly depending on temperature and ionic strength.

5. Frequently Asked Questions (FAQ)

Q1: Why use this specific formula for sodium phosphate?
A: For Na₃PO₄, the solution hydrolyzes to the intermediate form HPO₄²⁻, making the pH approximately the average of pKa₂ and pKa₃.

Q2: What are typical pKa values for phosphoric acid?
A: At 25°C, the typical values are pKa₁ ≈ 2.14, pKa₂ ≈ 7.20, and pKa₃ ≈ 12.67.

Q3: How accurate is this approximation?
A: This provides a good estimate but may vary slightly due to concentration effects, temperature, and ionic strength of the solution.

Q4: Can this calculator be used for other phosphate salts?
A: This formula is specific to trisodium phosphate (Na₃PO₄). Other phosphate salts require different calculations.

Q5: What factors affect the pKa values?
A: Temperature, ionic strength, and the presence of other ions can influence the apparent pKa values in solution.