Question

1) What is the predicted pH of 0.10 M ammonium acetate

2) What is the predicted pH of 0.10 M sodium bicarbonate

3) What is the predicted pH of 0.10 M iron (III) chloride (source of Fe(H₂O)₆³⁺ complex)

Answer 1

Q1.

1) What is the predicted pH of 0.10 M ammonium acetate

this is wek acid + weak base

since

NH4CH3COO wiol fform:

NH4+ + CH3COO-

NH4+ acts as an acid, CH3COO- as a base

pKa (NH4+) = 9.25; pKa(acetate) = 4.25

therefore,

pH = 7 approx... since both act as similar acid/base strenght

Q2.

Sodium Bicarboante --> NaHCO3

forms

NaHCO3 --> Na+ + HCO3-

Note tat HCO3- can act either as acid or base

so

pH = 1/2*(pKa1 + pKa2)

pH = 1/2*(6.37 + 10.32)

pH = 8.345 approx

Q3.

Fe(H2O)6+2 forms equilbirium:

[Fe(H2O)6]3+(aq) <--> [Fe(H2O)5OH]2+(aq) + H+(aq)

therefore, there are some H+ in solution

for this, Fe(H2O)63+ --> Fe(H2O)5OH2+ Ka = 1.84*10^-3

Ka = [H+][A-]/[HA]

1.84*10^-3 = x*x/(0.1-x)

x = 0.012675

pH= -log(h) = -log(0.012675) = 1.9