Question

Find equilibrium when 4 mM HCl, 4 mM HOCl, and 4 mM NH₄OH area added together to distilled water

A) Find all species present

B) Write Ct value expressions, and equilibrium expressions

C) Write the Charge Balance equations

Answer 1

A)

Species are: H⁺, Cl^-, OCl^-, NH₄⁺, OH^-.

B)

HCl H⁺+ Cl^- ,

equilibrium constant Ka = {[H⁺] .[Cl^-]} /[HCl]

Similarly, HOCl H⁺+ OCl^- ,

equilibrium constant Ka = {[H⁺] .[OCl^-]} /[HOCl]

and NH₄OH NH₄⁺+ OHl^- ,

equilibrium constant Ka = {[NH₄⁺] .[OH^-]} /[NH₄OH]

Ct(H⁺) = [HCl] + [HOCl]

Ct(Cl^-) = [HCl] + [HOCl]

Ct(OCl^-) = [HOCl]

Ct(NH₄⁺) = [NH₄OH]

Ct(OH^-) = [NH₄OH]

C)

Positive charges = [H⁺] + [NH₄⁺]

Negative charges = [Cl^-] + [OCl^-] + [OH^-]

Equating the two we get the charge balance equation

[H⁺] + [NH₄⁺] = [Cl^-] + [OCl^-] + [OH^-]