What is the pH of a solution obtained by dissolving two extra-strength aspirin tablets, containing 470 mg of acetylsalicylic acid each, in 240 mL of water?

2.58

Explanation:

Each tablet has a mass of 470 mg. The mass of 2 tablets is 2 * 470 mg = 940 mg = 0.940 g

The molarity of acetylsalicylic acid (aa) is:

M = mass of aa / molar mass of aa * liters of solution

M = 0.940 g / 180.16 g/mol * 0.240 L

M = 0.0217 M

Acetylsalicylic acid is a weak acid, so we can find [H⁺] using the following expression.

[H⁺] = √ (Ca * Ka)

where,

Ca: concentration of the acid

Ka: acid dissociation constant

[H⁺] = √ (0.0217 * 3.24 * 10⁻⁴)

[H⁺] = 2.65 * 10⁻³ M

The pH is:

pH = - log [H⁺] = - log 2.65 * 10⁻³ = 2.58