Question

Calculate [H3O+] for the following solutions:

A. 7.40 x 10^-3 M HBr

B. 1.80 x 10^-2 M KOH

Answer 1

a)

note that HBr is actually a strong acid and will dissociate completely as follows:

HBr(aQ) <--> H+(Aq) + Br-(aq)

for

pH = -log([H+])

calculate concentraiton of H+

[H+] = [HBr] = 7.4*10^-3 M

then

pH = -log(7.4*10^-3) = 2.13076

b)

similarly, KOH is a strong base so:

KOH --> K+ + OH- (completly)

so

[OH-] = [KOH] = 1.8*10^-2 M

calculate pOH

pOH = -log(OH-) = -log(1.8*10^-2)

pOH = 1.74472

since:

14 = pH + pOH

then

pH = 14-pOH = 14 - 1.74472

pH = 12.25528