# Triiodide ion gravimetric analysis Reaction Equation

Last week I did a gravimetric analysis from the following reaction.

$\ce{AgNO3 + (CH3)4N+I3- -> AgI(s) + (CH3)4N+NO3- + I2}$

The objective was to identify if my reactant was triiodide or pentaiodide. In order to find out we reacted $\ce{AgNO3}$ in excess so all iodide ions precipitated and no $\ce{I2}$ was formed. Then, $\ce{AgI}$ could be weighted and calculations would tell you the valence of the ion.

Question is, if no $\ce{I2}$ is formed, you expect to have $\ce{3 AgI}$ precipitating. But how do you balance the equation?? This is the unbalanced equation:

$\ce{AgNO3 + (CH3)4N+I3- -> 3AgI(s) + (CH3)4N+NO3-}$

I don't need the answer, I am just curious because my professor could not solve the problem.

Thank you and good luck!

• What is the oxidation state of iodine in $\ce{I3-}$? Without any redox reaction occurring, there's no way you can precipitate all three iodine atoms as $\ce{I-}$. – orthocresol Oct 9 '16 at 23:11