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The active ingredient in aspirin is acetylsalicylic acid. A 2.51 gram sample of acetylsalicylic acid required...

The active ingredient in aspirin is acetylsalicylic acid. A 2.51 gram sample of acetylsalicylic acid required 27.36ml of 0.5106 M NaOH for the complete reaction. The addition of 13.68 ml of 0.5106 M HCl to the flask containing the aspirin and the NaOH produced a mixture with a pH of 3.48. Based on this data, what is the molar mass of acetylsalicylic acid and the pka for aspirin?

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Answer #1

mass of aspirin = 2.51 g

moles of NaOH = 27.36 x 0.5106 / 1000

                         = 0.01397 mol

moles of HCl = 13.68 x 0.5106 / 1000

                     = 0.006985 mol

pH = pKa + log [base / acid]

3.48 = pKa + log [ 0.006985 /0.01397 - 0.006985 ]

pKa = 3.48

molar mass = 2.51 / 0.01397

molar mass = 180 g/mol

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