3. What is the percent dissociation of 0.10 M phenol? (The Ka value for phenol i

Question

3. What is the percent dissociation of 0.10 M phenol? (The Ka value for phenol is 1.3 x 10-10) 3. Sodium hypochlorite (NaOCI, 74.44 g/mol) is a common ingredient in household bleach. What is the pH of a particular brand of bleach that has a density of 1.08 g/mL and is 4.00% NaOCl by mass? (pKa of HOCl = 7.46) 3. What is the pH of a solution prepared by dissolving 9.00 g sodium dihydrogen borate (83.8 g/mol) in 750 mL of a 0.0725 M boric acid? The Ka of boric acid is 5.4 x100. Ignore any volume change.

Explanation / Answer

3)

Phenol is a weak acid let us consider it as HA, phenoxide ion is A

Ka for 0.1 M phenol = 1.3x10-10

We know that for phenol:

Ka = x2/0.1-x

Since x is small we will consider 0.1-x as 0.1.

x2 = 1.3x10-11

x =[phenoxide ion, A] = 0.36x10-5

Percentage dissociation:[H+]/[HA] = (1.3x10-10)/ 0.36x10-5

[H+]/[HA] =0.36x10-4 = 0.36%

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