Ph Of Weak Base Formula

Weak Base pH Formula:

\[ pH = 14 - pOH; \quad pOH = \frac{1}{2} pK_b - \frac{1}{2} \log C \]

pH:

pOH:

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1. What is the Weak Base pH Formula?

The weak base pH formula calculates the pH of a solution containing a weak base using the base dissociation constant (pK_b) and concentration. This formula is derived from the equilibrium principles of weak base dissociation in aqueous solutions.

2. How Does the Calculator Work?

The calculator uses the weak base pH formula:

\[ pH = 14 - pOH; \quad pOH = \frac{1}{2} pK_b - \frac{1}{2} \log C \]

Where:

\( pH \) — pH value of the solution (unitless)
\( pOH \) — pOH value of the solution (unitless)
\( pK_b \) — Base dissociation constant (unitless)
\( C \) — Concentration of weak base (mol/L)

Explanation: The formula calculates pOH first using the relationship between base strength and concentration, then converts to pH using the water ion product relationship (pH + pOH = 14).

3. Importance of Weak Base pH Calculation

Details: Accurate pH calculation for weak base solutions is essential in pharmaceutical formulations, chemical synthesis, buffer preparation, and understanding acid-base equilibria in biological systems.

4. Using the Calculator

Tips: Enter pK_b value (positive number) and concentration in mol/L (must be greater than 0). The calculator will compute both pH and pOH values for the weak base solution.

5. Frequently Asked Questions (FAQ)

Q1: What is considered a weak base?
A: A weak base is one that only partially dissociates in water, typically with pK_b values between 1 and 14. Examples include ammonia, amines, and carbonate ions.

Q2: When is this formula applicable?
A: This formula applies to monoprotic weak bases in dilute aqueous solutions where autoionization of water can be neglected and concentration is significantly greater than [OH⁻].

Q3: What are typical pK_b values for common weak bases?
A: Ammonia (pK_b ≈ 4.75), methylamine (pK_b ≈ 3.36), pyridine (pK_b ≈ 8.75). Lower pK_b indicates stronger base.

Q4: How does concentration affect weak base pH?
A: Higher concentration generally results in higher pH (more basic solution), but the relationship is logarithmic rather than linear.

Q5: What are the limitations of this formula?
A: Not suitable for very concentrated solutions, polyprotic bases, or when significant ionic strength effects are present. For precise calculations, iterative methods may be needed.