The active ingredient in aspirin is acetylsalicylic acid 1HC9H7O42, a monoprotic acid with Ka = 3.3 * 10^-4 at 25 °C. What is the pH of a solution obtained by dissolving two extra-strength aspirin tablets, each containing 500 mg of acetylsalicylic acid, in 250 mL of water?

Verified step by step guidance

1. Calculate the total mass of acetylsalicylic acid by multiplying the mass of one tablet by the number of tablets.
2. Convert the total mass of acetylsalicylic acid to moles using its molar mass (180.16 g/mol).
3. Determine the concentration of acetylsalicylic acid in the solution by dividing the number of moles by the volume of the solution in liters.
4. Set up the expression for the acid dissociation constant (Ka) for acetylsalicylic acid: \( Ka = \frac{[H^+][A^-]}{[HA]} \), where [HA] is the initial concentration of the acid, and [H^+] and [A^-] are the concentrations of the hydrogen ion and the acetate ion at equilibrium.
5. Assume that the initial concentration of [H^+] and [A^-] is negligible, and solve for [H^+] using the approximation \( [H^+] = \sqrt{Ka \times [HA]} \), then calculate the pH using \( pH = -\log[H^+] \).