Question

Ferric chloride is used as a coagulant for drinking water treatment. It reacts with bicarbonate to form iron hydroxide precipitate as follows: FeCl3•7H2O + HCO3- ↔ Fe(OH)3(s) + CO2 + Cl- + H2O

(a) Balance the above reaction. Rewrite the complete balanced reaction.

(b) If 20 mg/L of ferric chloride are added to treat stream water, calculate the amount (mg/L) of ferric hydroxide sludge that will be formed.

Answer 1

(a)

balanced reaction :

FeCl3•7H2O + 3 HCO3-       --------------------------> Fe(OH)3(s) + CO2 + 3 Cl- + 7H2O

b)

FeCl3•7H2O + 3 HCO3-       --------------------------> Fe(OH)3(s) + CO2 + 3 Cl- + 7H2O

288.3 g                                                                      106.87 g

20 x 10^-3 g                                                                 ?

Fe(OH)3 mass = 20 x 10^-3 x 106.87 / 288.3

                          = 7.41 x 10^-3 g

                         = 7.41 mg /L

ferric hydorxide = 7.41 mg /L