Answer to Question #303649 in General Chemistry for Jacey

Question

Common aspirin is acetylsalicylic acid, which has the structure shown below and a pKa of 3.5. Calculate the pH of a solution in which one normal adult dose of aspirin (650 mg

mg ) is dissolved in 6.0 ounces of water.

Answer 1

Aspirin is a weak acid.

pH of an weak acid = .5pKa - .5logC

C is the concentration in molarity

Molecular weight of aspirin =180.158 g/mole

650mg = (.650/180.158)moles

= .0036 mole

6 ounce = 177.282 ml

Concentration of the solution = (.0036/.177282) M

=0.02 M

Therefore pH of the solution is

= .5*3.5 - .5log0.02

=0.9