1. Calculate the pH during the titration of 10.00 mL of 0.400 M hypochlorous aci

Question

1. 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. 2.What is the pH after 2.40 mL of NaOH are added?

Explanation / Answer

HOCl dissociates: HOCl? H+ + OCl- Calculate the [H+] for 0.400M HOCl Ka = [H+] * [OCl]/[HOCl] We use two pieces of information: [H+] = [OCl-] [HOCl] is >>>> [H+], so we can use [HOCl] in the original soltion, and ignore the small amount that has issociated Substitute: 3.0*10^-8 = [H+]²/ 0.400 [H+}² = (3.0*10^-8) * 0.400 [H+]² = 1.2*10^-8 [H+} = 1.095*10^-4 pH = -log [H+] pH = -log (1.095*10^-4) pH = 3.96 Initial pH of acid = 3.96

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