The active ingredient in aspirin is acetylsalicyclic acid (HC9H7O4) a monoprotic

Question

The active ingredient in aspirin is acetylsalicyclic acid (HC9H7O4) a monoprotic acid with Ka= 3.3 x 10^-4 at 25 degrees celcius. What is the pH of a solution obtained by dissolving two extra-strength aspirin tablets, containing 470 mg of acetylsalicyclic acid each, in 220 mL of water? The active ingredient in aspirin is acetylsalicyclic acid (HC9H7O4) a monoprotic acid with Ka= 3.3 x 10^-4 at 25 degrees celcius. What is the pH of a solution obtained by dissolving two extra-strength aspirin tablets, containing 470 mg of acetylsalicyclic acid each, in 220 mL of water?

Explanation / Answer

Ka = 3.3*10^-4

Ka = [H+][A-]/[HA]

[HA] = #* mass/(MW*L) = 2*(470*10^-3)/(180.157 *0.22) = 0.0237166 M

then

[H+]= x= [A-]

[HA] = M-x = 0.0237166 -x

Ka = [H+][A-]/[HA]

3.3*10^-4 = x*x/(0.0237166 -x)

x = [H+] = 0.002636

pH = -log(0.002636) = 2.5790

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