Question

Why would the actual coefficients of a ferrous ammonium sulfate hexahydrate and the potassium iron oxalate complex in a balanced chemical equation describing the overall process not be required to compute the predicted weight of the product?

Answer 1

Ans: Ferrous ammonium sulfate, Fe(NH4)2(SO4)2·6H2O, when dissolved in excess oxalic acid, H2C2O4 , various reacton take place are:-
2Fe 2+	=	2Fe 3+ + 2e-	(2e- "lost")
H2O + HO2- + 2e-	=	3OH-	(2e- "gained")
H2O + HO2- + 2Fe 2+	=	2Fe3+ + 3OH-	(net reaction)

FeC₂O₄ is the source of the Fe ²⁺ and over all reaction is

Fe(NH₄)₂(SO₄)₂· 6H₂O + H₂C₂O₄ = FeC₂O₄(s) + H₂SO₄ + (NH₄)₂SO₄ + 6H₂O(l)

The OH- ion concentration of the solution is high enough so that some of the Fe3+ reacts with OH- to form ferric hydroxide (brown precipitate) asFe3+ + 3OH- = Fe(OH)3(s)
With the addition of more H2C2O4, the Fe(OH)3 dissolves and the soluble complex K3[Fe(C2O4)3]· 3H2O is formed according to: 3K2C2O4 + 2Fe(OH)3(s) +3H2C2O4 = 2K3[Fe(C2O4)3]· 3H2O + 3H2O

The complexity of the series of reactions described in equations 1 - 4 may be greatly simplified by following the Fe²⁺/Fe³⁺ ion throughout. One discovers that for every mole of Fe(NH₄)₂(SO₄)₂]. 6H₂O used as starting material, one mole of K₃[Fe(C₂O₄)₃].3H₂O will be obtained as the final product.

Fe(NH4)2(SO4)4. 6H2O + H2C2O4	=	FeC2O4 + ......etc.		(Fe2+ = Fe2+)
FeC2O4 + K2C2O4 + H2O2	=	Fe(OH)3(s) + .....etc		(Fe2+ = Fe3+)
Fe(OH)3 + H2O2 + K2C2O4	=	K3[Fe(C2O4)3]·3H2O + ..etc		(Fe3+ = Fe3+)