Question

please explain

Bleach is a common household cleaner that removes stains, disinfects, and can be used to whiten clothes. The % ionization curve for hypochlorite is shown to the right. The primary ingredient of household bleach is sodium hypochlorite (NaOCI), which is typically in a concentration around 0.67 M of the base OCI. What is the pH of household bleach? 100T.-L. % OCI --- - -17 50 . 7 9 11 13 5 pH O A 3.3 O B 10.7 OC 6.6

Answer 1

From the given graph, when concentration if OCl^- is 50 %, then pH is 7.5

pOH = 14 - pH

pOH = 14 - 7.5

pOH = 6.5

When concentration of OCl^- reaches 50%, this means half-equivalence point is reached in titration and pK_b of OCl^- equals to pOH at that point.

pK_b = pOH

pK_b = 6.5

K_b = 10^-pK_b

K_b = 10^-6.5

K_b = 3.16 x 10^-7

initial concentration of OCl^- = 0.67 M

ICE table	OCl- (aq)	H2O	$\rightleftharpoons$	HOCl (aq)	OH-
Initial conc.	0.67 M	-		0	0
Change	-x	-		+x	+x
Equilibrium conc.	0.67 M - x	-		+x	+x

K_b = [HOCl]_eq[OH^-]_eq / [OCl^-]_eq

3.16 x 10^-7 = [(x) * (x)] / (0.67 M - x)

Solving for x, x = 4.6 x 10^-4 M

[OH^-] = x = 4.6 x 10^-4 M

pOH = -log[OH^-]

pOH = -log(4.6 x 10^-4 M)

pOH = 3.34

pH = 14 - pOH

pH = 14 - 3.34

pH = 10.7