tentukan pH larutan jika 50mL larutan HCl 0.1 M dicampurkan dengan 100 mL larutan NH3 0.2 M (Kb = 10pangkat-5)

dietahui :
M HCl = 0,1 M
V HCl = 50 mL
M NH3 = 0,2 M
V HCl = 100 mL

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1. menenukan mol
  # mol HCl = 0,1 . 50 mL = 5 mmol
  # mol NH3 = 0,2 . 100 mL = 20 mmol

2. tulis reaksinya
     HCl + NH3 --> NH4Cl
M : 5 mmol + 20 mmol --> -
R : 5 mmol + 5 mmol --> 5 mmol
----------------------------------------------------
S : -  + 15 mmol --> 5 mmol

3. menentukan pH
  [H+] = Kb . mol sisa basa/mol sisa garam
          = 10^-5 . 15/5
          = 10^-5 . 3
           = 3 . 10^-5
pOH = - log 3 . 10^-5
        = 5 - log 3
pH = 14 - (5 - log 3)
     = 9 + log 3

(maaf kalo salah)