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Calculate The Ph of A 0.20 M C2h5nh2 Solution

Reviewed by Calculator Editorial Team

Calculating the pH of a C2H5NH2 (ethylamine) solution involves understanding the relationship between the concentration of the weak base and the resulting pH. This guide provides a step-by-step explanation of the calculation process, including the formula, assumptions, and interpretation of results.

Introduction

Ethylamine (C2H5NH2) is a weak organic base that dissociates in water to form the ethylammonium ion (C2H5NH3+) and hydroxide ions (OH-). The pH of the solution depends on the concentration of the base and the equilibrium constants involved in its dissociation.

The pH calculation for a weak base solution involves several steps, including determining the dissociation constant (Ka), calculating the equilibrium concentrations, and finally computing the pH from the hydrogen ion concentration.

pH Calculation Formula

The pH of a weak base solution can be calculated using the following steps:

  1. Determine the dissociation constant (Ka) for the weak base.
  2. Calculate the equilibrium concentrations of the base and its conjugate acid.
  3. Compute the hydrogen ion concentration ([H+]).
  4. Calculate the pH from the hydrogen ion concentration.
pH = -log[H+] [H+] = sqrt(Ka * [C2H5NH2])

Where:

  • Ka is the dissociation constant for the weak base (ethylamine)
  • [C2H5NH2] is the molar concentration of ethylamine
  • [H+] is the hydrogen ion concentration

The dissociation constant (Ka) for ethylamine is approximately 4.4 × 10⁻⁴ at 25°C. This value may vary slightly depending on temperature and other conditions.

Worked Example

Let's calculate the pH of a 0.20 M ethylamine solution using the formula:

pH = -log(sqrt(4.4 × 10⁻⁴ × 0.20)) pH = -log(sqrt(8.8 × 10⁻⁵)) pH = -log(2.966 × 10⁻³) pH ≈ 2.53

This calculation shows that a 0.20 M ethylamine solution has a pH of approximately 2.53, indicating it is acidic due to the formation of the ethylammonium ion.

Concentration (M) Calculated pH Solution Type
0.10 2.35 Acidic
0.20 2.53 Acidic
0.50 2.85 Acidic

Interpreting Results

The pH of a weak base solution provides several important insights:

  • The pH decreases as the concentration of the weak base increases, indicating a more acidic solution.
  • A pH below 7 confirms that the solution is acidic due to the formation of the conjugate acid.
  • The pH calculation helps determine the degree of dissociation and the equilibrium state of the solution.

Understanding the pH of a weak base solution is crucial in various chemical applications, including buffer solutions, titrations, and chemical synthesis.

FAQ

What is the pH of a 0.20 M C2H5NH2 solution?
The pH of a 0.20 M ethylamine solution is approximately 2.53, indicating an acidic solution due to the formation of the ethylammonium ion.
How does the concentration of C2H5NH2 affect the pH?
As the concentration of ethylamine increases, the pH decreases, making the solution more acidic. This is because more of the base dissociates to form the conjugate acid.
What is the dissociation constant for ethylamine?
The dissociation constant (Ka) for ethylamine is approximately 4.4 × 10⁻⁴ at 25°C. This value is used in the pH calculation formula.
Why is the pH of a weak base solution acidic?
The pH of a weak base solution is acidic because the base dissociates to form the conjugate acid, which increases the concentration of hydrogen ions in the solution.