Question

Calculate the pH when we add: 

(a) 0 mL (b) 9 mL (c) 20 mL (d) 25 mL NaOH solution whose concentration is 0.06 M to a 10 mL sample of acetic acid. The concentration of the acetic acid is unknown (K_a= 1.86 × 10^–5). First, calculate the concentration of the acetic acid if we know that 20 mL of NaOH is consumed up to the equivalence point. What kind of indicator would you use for this titration?

Answer 1

Results: 

(a) c(acetic acid) = 0.12 mol/dm³  

(b) at the beginning of the titration: 0 ml of base was added (weak acid)→ pH = 2.826

(c) After the addition: 9 ml of base (buffer system) → pH = 4.643 

(d) After the addition: 20 ml of base (weak base)→ pH = 8.666

(e) After the addition: 25 ml of base (excess of strong base)→ pH = 11.933