Question

Balance the equations.

Fe3+(aq) + SCN–(aq) <--> FeSCN2+

Ag+(aq) + SCN–(aq) <--> Ag(SCN)4 ^3-

FeSCN2+(aq) + Ag+(aq) <--> Ag(SCN)43- + Fe3+(aq)

Use Le Chatelier’s principle to explain the different colors and how they relate to the disturbance of the equilibrium.

Answer 1

To balance any equation it is necessary that total charge on reactant side and total charge on product side should be same (with sign)

Fe3+(aq) + SCN_ (aq)  -------> Fe(SCN)^2+ (It is already balanced as reactant side has +3-1=+2 which is same in product side

Ag+(aq) + 4SCN_(aq) ----------> Ag(SCN)4 ^3- (here we multiply the thiocyanate with 4 to get the charge balanced)

4Fe(SCN)^2+(aq) + Ag+(aq) --------->  Ag(SCN)4 ^3- + 4Fe3+(aq) (here we multiply iron(II) thiocyanate with 4 and iron(III) with 4 to balance the equation)

In the reaction as the concentration of silver ion or iron(II) thiocyanate concentration was decreased, then the to undo the effect equilibrium shifts backward giving blood red color due to iron(II) thiocyanate and vice versa.Similarly if the concentration of Fe3+ was increased it will shift the reaction toward reactant side giving more intensified solution.