Question

HW 14 © Alyson Smit 320 - WANG > Activities and Due Dates > HW 14 gnment Score: 91.7% Resources Gt Give Up? Hine Check Answ cion 17 of 25 > Attempt 3 If the K, of a weak base is 6.9 x 10, what is the pH of a 0.40 M solution of this base? pH MacBook Pro Tel < > ?

Answer 1

weak base BOH dissociate as

BOH + H2O    $1585514342543_blob.png$ B+(aq) + OH-(aq)

Kb = [B+] [OH-] / [BOH]

but [B+] = [OH-]

consider [B+] = [OH-] = X

then Kb = [X] [X] / [BOH]

Kb = X2 / [BOH]

X2 = Kb X [BOH]

substitute the value

X2 = (6.9 X 10-6) X (0.40) = 2.76 X 10-6

X = 0.00166 M

[B+] = [OH-] = X = 0.00166 M

[OH-] = 0.00166 M

pOH = -log [OH-] = -log (0.00166) = 2.78

pH = 14 - pH = 14 - 2.78 = 11.22

pH of 0.40 M weak base = 11.22