Calculate The Ph At The Equivalence Point For The Titration Of 0.140 M Methylamine

pH Calculation Formula:

\[ pH = \frac{1}{2} pK_w + \frac{1}{2} pK_b + \frac{1}{2} \log(0.140) \]

Water Ionization Constant (pKw):

(dimensionless)

Base Dissociation Constant (pKb):

(dimensionless)

Concentration (C):

mol/L

Calculated pH:

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1. What is the pH Calculation for Methylamine Titration?

This calculator determines the pH at the equivalence point for the titration of 0.140 M methylamine solution. At the equivalence point of a weak base-strong acid titration, the solution contains the conjugate acid of the weak base, resulting in an acidic pH.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ pH = \frac{1}{2} pK_w + \frac{1}{2} pK_b + \frac{1}{2} \log(0.140) \]

Where:

\( pK_w \) — Water ionization constant (typically 14.00 at 25°C)
\( pK_b \) — Base dissociation constant of methylamine (3.36)
\( C \) — Concentration of methylamine (0.140 mol/L)

Explanation: This formula calculates the pH at the equivalence point for the titration of a weak base with a strong acid, where the solution contains the conjugate acid of the weak base.

3. Importance of pH Calculation at Equivalence Point

Details: Determining the pH at the equivalence point is crucial for selecting appropriate indicators in acid-base titrations and understanding the properties of the resulting solution.

4. Using the Calculator

Tips: Enter the pKw value (typically 14.00 at 25°C), pKb for methylamine (3.36), and the concentration of methylamine (0.140 mol/L). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: Why is the pH acidic at the equivalence point?
A: Methylamine is a weak base, so its conjugate acid (methylammonium ion) hydrolyzes in water, producing H₃O⁺ ions and resulting in an acidic pH.

Q2: What is the typical pKb value for methylamine?
A: The base dissociation constant pKb for methylamine is approximately 3.36 at 25°C.

Q3: Does temperature affect the calculation?
A: Yes, pKw changes with temperature (13.99 at 0°C, 13.68 at 50°C), which would affect the calculated pH.

Q4: Can this calculator be used for other weak bases?
A: Yes, but you would need to input the appropriate pKb value for the specific weak base being titrated.

Q5: Why is the concentration term included in the formula?
A: The concentration affects the extent of hydrolysis of the conjugate acid, which influences the final pH at the equivalence point.