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. How many mL of NaOH are added to reach the equivalence point? 3. What is the pH after 2.40 mL of NaOH are added? 4. What is the pH after 5.00 mL of NaOH are added? 5. What is the pH at the equivalence point?

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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