Question

a volume of 34.0 mL of 0.100 M KOH was required to reach the endpoint in the titration of a 10.0 mL solution of CH3COOH(pKa= 4.74). Find the initial pH of the CH3COOH solution.(

a)0.61

b)1.61

(c)2.61

(d)3.61

(e)4.61

Answer 1

answer : (c) 2.61

solution:

at end point

millimoles of acid = millimoles base

10.0 x C1 = 0.100 x 34

          C1 = 0.34 M

acid , CH3COOH concentration = 0.34 M

pH = 1/2 [pKa -log C ]

pH = 1/2 [4.74 -log 0.34 ]

pH = 2.61