Unless otherwise specified assume infinite dilution (i.e., activity coefficient

Question

Unless otherwise specified assume infinite dilution (i.e., activity coefficient 1). Please ad here o the problem solving protocol outlined in class. 1) In hot tubs and spas, Br(+D in the form of hypobromous acid (HOBn)(pKa-8.63) is often used to disinfect water. Predict the pH of a 5 x 104 M solution of bromine disinfectant i it is added to pure water: a. as HOBr? Write out the electroneutrality equation for this system. Write out an expression to solve for pH in this system (please simplify so that [H'] is the only variable. Solve the pH value using C-pH diagram as NaOBr? [solve without making any simplifications] Write out the electroneutrality equation for this system. Write out an expression to solve for pH in this system (please simplify so that [H'] is the only variable Solve the pH value using C-pH diagram b.

Explanation / Answer

Ka = 2.4 x 10-9

a)

HOBr <-> H+ and OBr-

Ka = [H+][OBr-] / (HOBr)

2.4 x 10-9 = (x)(x)/(5*10^-4 -x)

Solve for x

x = 1.09*10^-6

thenn

pH = -log(H) = -log(x) = -log(1.09*10^-6) = 5.96

b)

if NaOBr

this will form

OBr- + H2O <-> OH- + HBr

Kb = [OH][HOBr]/[OBr]

Kb = Kw/Ka = (10^-14)/(2.4*10^-9) = 0.00000416666

then

0.00000416666 = (x*x)/(5*10^-4 -x)

sovle for x

x = 4.6*10^-5

pOH = -log(x) = -log(4.6*10^-5) = 4.34

pH = 14-pOH = 14-4.34 = 9.66

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