In your lab you are studying aspirin, and its acid/base properties. you find that a 1.00 l of a 0.500 m solution of aspirin has a ph of 1.86. you are interested in learning about the % dissociation in a buffered solution of aspirin, so you make a new 1.00 l solution containing 0.500 moles of aspirin and 0.25 moles of the sodium salt of aspirin. what will the % dissociation be in this new buffered solution?

Explanation:

The given data is as follows.

Initial volume of aspirin = 1.00 L

Initial concentration of aspirin = 0.500 M

Initial pH = 1.86

Hence, hydronium ion concentration will be calculated as follows.

               pH =

or,              

                               =

                                =

As, buffer containing aspirin and its conjugate base is formed in 1 L solution.

Hence, moles of aspirin are 0.500 moles and moles of the conjugate base are 0.25 moles.

So, upon dissociation the concentration of acetylsalicylate ion and hydronium ion are the same.

Hence, value will be calculated as follows.

              =

                           =

                           =

Also,      

                          =

                           = 3.41

Now, using Henderson-Hasselbalch equation we determine the pH as follows.

      pH =

            = 3.41 +

            = 3.11

Determine the hydronium ion concentration of buffer as follows.

                            =

                            = M

Therefore, we calculate the recent dissociation as follows.

          % dissociation =

                                   =

                                   = × 100

                                   = 0.15%

Thus, we can conclude that the value of % dissociation of new buffered solution is 0.15%.

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)