In: Chemistry
Find the pH during the titration of 20.00 mL of 0.1000 M butanoic acid, CH3CH2CH2COOH (Ka = 1.54 x 10^-5), with 0.1000 M NaOH solution after the following additions of titrant (a) 14.00 mL (b) 20.30 mL (c) 26.00 mL
Ka = 1.54 x 10^-5
pKa = -log Ka
pKa = 4.81
a)
millimoles of acid = HA =20 x 0.1 = 2
millimoles of OH- = 14 x 0.1 = 1.4
HA + OH- -----------------> H2O + A-
2 1.4 0 0
0.6 0 1.4
pH = pKa + log [A-/ HA]
pH = 4.81 + log (1.4 / 0.6)
pH = 5.18
(b) 20.30 mL
base millimoles dominent
[OH-] = 20.30 x 0.1 - 20 x 0.1 / (20 + 20.30)
= 7.44 x 10^-4 M
pOH = -log [OH-] = 3.13
pH + pOH = 14
pH = 10.87
(c) 26.00 mL
[OH-] = 2.6 - 2.1 / (46) = 0.0109M
pOH = 1.88
pH = 12.12