In: Chemistry
Calculate the pH during the titration of 10.00 mL of 0.400 M
hypochlorous acid with 0.500 M NaOH. First what is the initial pH
(before any NaOH is added)?
The Ka for HOCl is 3.0 x 10-8 M.
What is the pH after 6.20 mL of NaOH are added?
What is the pH after 9.40 mL of NaOH are added?
What is the pH when half the acid has been neutralized?
What is the pH after 18.90 mL of NaOH are added?
pKa = -log Ka
pKa = 7.52
1) before any NaOH is added
pH = 1/2 [pKa - log C]
pH = 1/2 [7.52 - log 0.40]
pH = 3.96
2) What is the pH after 6.20 mL of NaOH are added?
millimoles of HClO = 0.4 x 10 = 4
millimoles of NaOH = 6.2 x 0.5 = 3.1
HClO + NaOH ----------------------> NaClO + H2O
4 3.1 0 0
0.9 0 3.1 3.1
pH = pKa + log [salt / acid]
pH = 7.52 + log (3.1 / 0.9)
pH = 8.06
3) What is the pH after 9.40 mL of NaOH are added?
millimoles of HClO = 0.4 x 10 = 4
millimoles of NaOH = 9.4 x 0.5 = 4.7
[OH-] = 0.7 / (10 + 9.4) = 0.0361 M
pOH = 1.44
pH + POH = 14
pH = 12.56
4) What is the pH when half the acid has been neutralized
here pH = pKa
pH = 7.52
5) What is the pH after 18.90 mL of NaOH are added?
pH = 13.28