Question

In: Chemistry

Calculate the pH during the titration of 10.00 mL of 0.400 M hypochlorous acid with 0.500...


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?

Solutions

Expert Solution

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


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