Calculate the pH of each of the following solutions?

Question

A. A 0.100 M propanoic acid 

B. A 0.100M sodium propanoate

C. Pure H2O

D. A mixture containing 0.100M HC3H5O2 and 0.100M NaC3H5O2

Answer 1

A.  Need the Ka for propanoic acid and the concentration.   Then ...

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

 

B. Kb = Kw/Ka propanoic acid. Once you have Kb,

A- + H2O ==>HA + OH- and Kb=[HA][OH-]/[A-]

Solve for [OH-] and the pH. 

 

C. H2O ==> H+ + OH-

1x10^-14 = x²

x = 1x10^-7 = [H+] and pH = 7

 

D.  Since it is a buffer and acid = salt, then pH = pKa of the acid. Look it up.