Home
Back
Weak Base pH Approximation:
| From: | To: |
The weak base pH approximation estimates the pH of a solution containing a weak base using the formula: pH = 14 - ½ pKb - ½ log C. This equation provides a simplified method to calculate pH when dealing with weak bases in aqueous solutions.
The calculator uses the weak base approximation equation:
Where:
Explanation: This approximation assumes that the weak base is only partially dissociated and that the concentration of OH⁻ ions can be estimated using the square root of (Kb × C).
Details: Accurate pH calculation is crucial for understanding chemical reactions, biological systems, and industrial processes. pH affects reaction rates, solubility, and biological activity.
Tips: Enter the base dissociation constant (Kb) and concentration (C) in mol/L. Both values must be positive numbers. The approximation works best for weak bases with concentrations significantly higher than the Kb value.
Q1: When is this approximation valid?
A: This approximation is valid when C >> [OH⁻], which is typically true for weak bases with small Kb values and reasonable concentrations.
Q2: What are the limitations of this approximation?
A: The approximation becomes less accurate for very dilute solutions or for bases that are not particularly weak (larger Kb values).
Q3: How is pKb related to Kb?
A: pKb is the negative base-10 logarithm of Kb: pKb = -log₁₀(Kb). A smaller pKb value indicates a stronger base.
Q4: Can this formula be used for strong bases?
A: No, strong bases are completely dissociated, so their pH calculation is straightforward: pH = 14 + log(C).
Q5: What is the typical range for Kb values?
A: For weak bases, Kb typically ranges from 10⁻² to 10⁻¹², with most common weak bases having Kb values between 10⁻⁴ and 10⁻⁸.