Calculate The Percent Ionization of 0.0075 M Butanoic Acid

Butanoic acid (C₄H₈O₂) is a weak organic acid that partially dissociates in aqueous solution. This calculator helps determine the percent ionization of 0.0075 M butanoic acid, providing insights into its dissociation behavior.

Introduction

When butanoic acid dissolves in water, it undergoes partial dissociation according to the following reaction:

C₄H₈O₂(aq) ⇌ C₄H₇O₂⁻(aq) + H⁺(aq)

The percent ionization is a measure of how much of the acid molecules dissociate into ions. For butanoic acid, the dissociation constant (Kₐ) is approximately 1.55 × 10⁻⁵ at 25°C.

Formula

The percent ionization can be calculated using the following formula:

% Ionization = (√(4Kₐ × C) / C) × 100

Where:

Kₐ = Acid dissociation constant (1.55 × 10⁻⁵ for butanoic acid)
C = Initial concentration of the acid (0.0075 M in this case)

This formula assumes the concentration of H⁺ from water is negligible compared to the concentration of H⁺ from the acid dissociation.

Calculation

Using the given values:

% Ionization = (√(4 × 1.55 × 10⁻⁵ × 0.0075) / 0.0075) × 100

Calculating step by step:

Multiply 4 × Kₐ × C: 4 × 1.55 × 10⁻⁵ × 0.0075 = 4.65 × 10⁻⁷
Take the square root: √(4.65 × 10⁻⁷) ≈ 6.82 × 10⁻⁴
Divide by concentration: 6.82 × 10⁻⁴ / 0.0075 ≈ 0.091
Multiply by 100 to get percentage: 0.091 × 100 ≈ 9.1%

The percent ionization of 0.0075 M butanoic acid is approximately 9.1%.

Interpretation

A 9.1% ionization means that about 9.1% of butanoic acid molecules in solution have dissociated into ions. This relatively low value indicates butanoic acid is a weak acid, as expected for organic acids with a carboxyl group.

Comparing with other weak acids:

Acid	Kₐ (25°C)	% Ionization at 0.0075 M
Acetic acid	1.8 × 10⁻⁵	10.2%
Butanoic acid	1.55 × 10⁻⁵	9.1%
Formic acid	1.8 × 10⁻⁴	14.8%

This comparison shows butanoic acid is slightly weaker than acetic acid but stronger than formic acid at the same concentration.

Frequently Asked Questions

What is the difference between ionization and dissociation?: Ionization refers to the process of forming ions, while dissociation specifically refers to the breaking apart of molecules into ions. In this context, they are often used interchangeably.
How does temperature affect the percent ionization?: The dissociation constant Kₐ increases with temperature, which would generally increase the percent ionization for a given concentration. However, the relationship is complex and depends on the specific acid.
Can I use this formula for other weak acids?: Yes, the formula can be applied to any weak acid where the concentration of H⁺ from water is negligible compared to the concentration of H⁺ from the acid dissociation.
What factors affect the percent ionization?: The primary factors are the acid dissociation constant (Kₐ), the initial concentration of the acid, and the temperature of the solution.

About this calculator

Written by Calculator Editorial TeamPractical calculator research and UX writing

Reviewed by Practical Tools ReviewFormula logic, assumptions, and usability checks

Updated June 25, 2026. Formulas, assumptions, and limitations are shown directly on this page.

Formula and Sources

The percent ionization is calculated using the standard formula for weak acids: