Question

calculate the pH of a buffer solution prepared with 500 mg/L acetic acid (Ch3COOH; pKa=4.74) and...

calculate the pH of a buffer solution prepared with 500 mg/L acetic acid (Ch3COOH; pKa=4.74) and 200 mg/L sodium acetate (NaCH3COO) under the following conditions:

a) initially

b) after 20 mg/L of HCl is added

c) after 20 mg/L of NaOH is added

Homework Answers

Answer #1

conc of CH3COOH   = 500mg/L

conc of CH3COONa    = 200mg/L

PH   = Pka + log[CH3COONa]/[CH3COOH]

      = 4.74 + log200/500

     = 4.74 -0.3979   = 4.3421

b. after addition of 20mg/L of HCl

con of CH3COONa = 200-20 = 180mg/L

conc of CH3COOH   = 500+20 = 520mg/L

PH = PKa + log[CH3COONa]/[CH3COOH]

     = 4.74 + log180/520

    = 4.74-0.4607   = 4.2793

c. after addition of 20mg/L

conc of CH3COONa   = 200+20 = 220mg/L

conc of CH3COOH   = 500-20    = 480mg/L

PH = Pka + log[CH3COONa]/[CH3COOH]

     = 4.74 + log220/480

     = 4.74-0.3388   = 4.4012 >>>>answer

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