Question

Distilled white vinegar is used for cooking but can also be used in many applications for cleaning. The active ingredient in vinegar is acetic acid (, ). If a brand of household vinegar produces a pH of 3.5, what is the initial molar concentration of acetic acid (assuming it is the only substance contributing to pH)

Answer 1

5.7 × 10⁻³ M

Step-by-step explanation:

Step 1: Given and required data

pH of the solution: 3.5

Ka of acetic acid: 1.8 × 10⁻⁵

Step 2: Calculate the concentration of H⁺

pH = -log [H⁺]

[H⁺] = antilog -pH = antilog -3.5 = 3.2 × 10⁻⁴

Step 3: Calculate the initial molar concentration of acetic acid (Ca)

Acetic acid is a weak acid. We can calculate its initial concentration using the following expression.

Ca = [H⁺]²/Ka

Ca = (3.2 × 10⁻⁴)²/1.8 × 10⁻⁵

Ca = 5.7 × 10⁻³ M