Question

A typical aspirin tablet contains 327 mg of acetylsalicylic acid, HC9H7O4. Calculate the pH of a solution that is prepared by dissolving one aspirin tablet(s) in one cup (237 mL) of solution. Assume the aspirin tablets are pure acetylsalicylic acid, Ka = 3.3

Answer 1

Answer:

2.8

Explanation:

First, we will calculate the molarity of the acetylsalicylic acid solution.

M = mass of solute (g) / molar mass of solute × volume of solution (L)

M = 0.327 g / 180.158 g/mol × 0.237 L

M = 7.66 × 10⁻³ M

For a weak acid such as acetylsalicylic acid, we can find the concentration of H⁺ using the following expression.

[H⁺] = √(Ca × Ka)

where,

Ca: concentration of the acid

Ka: acid dissociation constant

[H⁺] = √(7.66 × 10⁻³ × 3.3 × 10⁻⁴)

[H⁺] = 1.6 × 10⁻³ M

The pH is:

pH = -log [H⁺]

pH = -log 1.6 × 10⁻³ = 2.8