9 Write the chemical reactions that represents the two buffe

9) Write the chemical reactions that represents the two buffer regions created by the titration of HS with KOH. Write expressions for the Ka of the acid in each of these regions and an expression for the pH

Solution

9)

H2S ----------------> HS-   +   H+    ,   Ka1

Ka1 = [HS-] [H+] / [H2S]

HS-   ---------------> S2- +   H+     ,    Ka2

Ka2 = [S2-][H+] / [HS-]

reaction with KOH :

H2S +    KOH    ------------------> KHS   + H2O

pH = pKa + log [salt / base]

pH = pKa1 + log [KHS / H2S]

HS- +   KOH    ------------------> S2-    +   H2O

pH = pKa2 + log [S2- / HS-]

buffer regions. HS- / H2S ,    S2- / HS-