Question

F. pH of Buffer after the addition of the Strong Base 1. Calculate the expected pH of this solution. 50.0 mL buffer + 2.0mLION NAOH pH 2. Measured pH of this solution. pH 4.59 3. What is the percent error between the calculated and measured value? What are some of the possible sources of this error? % error

Answer 1

F) 50 ml buffer contains 25 ml CH3COOH,25 ml CH3COONa.

No of mol of CH3COOH = 25*1 = 25 mmol

No of mol of NaOH = 25*1 = 25 mmol

after addition of NaOH,

pH of acidic buffer = pka + log(CH3COONa+NaOH/CH3COOH-NaOH)

pka of CH3COOH = 4.74

No of mol of NaOH added = 2*1 = 2 mmol

pH = 4.74+log((25+2)/(25-2))

pH = 4.81

Theoretical pH = 4.81

2) Measured (Experimental) pH = 4.59

    Theoretical pH = 4.81

%error = (Theoretical- Experimental)/Theoretical*100

        = (4.81-4.59)/4.81*100

        = 4.57%