Question

Theory: Tin (II) Iodide is not a thermodynamically favored substance. What this means is that if you mix Tin and Iodine, nothing will happen. So Tin(II) chloride + Zinc(II) iodide is used instead to synthesize Tin(II) iodide.

Can I have an explanation of why this is? I am looking at the reduction potentials and it seems the reaction is spontaneous however, so I am confused.

Answer 1

Zn has position above Sn in electrochemical series. It is based on the reduction potentials of elements.

As we know that when we mix tin into Iodine, it would not react since reduction potential of I2 is +0.535 V and that of the Tin is -0.14 V.

Though Tin is metal it can’t give readily electron to I2 due to less positive electrode potential. But when we Zn that has reduction potential = -0.76 V which is very less negative than Sn and that could reduce I2 and so we can get ZnI2.

Cl2 has more positive reduction potential than I2 so it Cl2 is easily reduced by Sn ( Tin) and form SnCl2.

When we have SnCl2 and ZnI2 then Zn replaces Cl2 From SnCl2 and forms ZnCl2 and SnI2.

As Sn2+ already is oxidized form and I- is in reduced form so no need to provide extra driving force so this is possible.