Question

8. Determine the pH for a solution that is

a) 0.762 M HC₄H₇O₂ and 0.762 M NaC₄H₇O₂

b) 0.478 M NH₃ and 0.458 M NH₄ClO₄

c) 0.671 M HNO₃ and 0.521 M HC₇H₅O₂

Answer 1

a)) pH = pka + log [NaC4H6O2] /[HC4H7O2]

pH = 4.86 + log ( 0.762/0.762) = 4.86     ( pka taken from web)

b) pOH = pkb + log [NH4ClO] /[NH3]    

           = 4.745 + log ( 0.458/0.478)    = 4.75

pH = 14-4.75 = 9.25

c) HNO3 is strong acid and HC7H5O2 is weak acid

strong acid contributes major H+ since strong acid dissociates completely

[HNO3] =[H+] = 0.671

pH = -log [H+] = -log ( 0.671) = 0.173