Final answer:
To calculate the pH of acetic acid or acetylsalicylic acid solutions, use the ICE table method to find [H+] at equilibrium and then apply the pH formula. Assumptions can simplify calculations, but may require solving a quadratic equation if invalid.
Step-by-step explanation:
To calculate the pH of a 0.313 M aqueous solution of acetic acid (CH3COOH) with a Ka of 1.8 x 10-5, first determine the concentration of hydrogen ions [H+] at equilibrium using the ICE table approach and the formula:
[H+] = √(Ka × [acid Initial])
Once [H+] is calculated, use the equation pH = -log[H+] to find the pH. Typically, some assumptions are made such that the initial concentration of acetic acid does not change significantly upon dissociation, meaning the change in concentration 'x' of H+ is small relative to the initial concentration of the acid.
Next, to calculate the pH of a 0.0267 M aqueous solution of acetylsalicylic acid (aspirin) with a Ka of 3.0 x 10-4, follow the same ICE table method and assumptions.
For both of these calculations, once [H+] is known, apply the formula for pH. If needed, solve quadratic equations when assumptions about 'x' being small are not valid.