Two days ago I make one ordinary experiment: Iodine solution and Ammonia

I've got a black precipitate, then I decided to put in the jar Na2CO3 solution. Then I added CH3COOH.

After that reaction NaHCO3 + CH3COOH → CH3COONa + H2O + CO2, the whole thing became ORANGE!?

Have any one have an idea what have happend? I am pretty sure that there is hydroiodic acid (HI), but what else and the main question: WHY IT'S ORANGE?

iodine is orange/brown in aqueous solution. Perhaps the addition of the other ionic substances increased the ionic concentration, increasing the solubility of the iodine in the water.

Yup, you are right (Le Chatelier's principle take an action here) Thank you!

But, anyway, the experiment is colorful

I think the actual orange species is [ce]I3-[/ce], which requires protons to be present. Perhaps it was the acetic acid that did it. Did you measure the pH? did you add enough acid to reverse the increased pH that resulted from the addition of ammonia and acetate?

pH<7, but not sure what is the exact pH

OK pH<7 explains it, i think. The [ce]I3-[/ce] exists in equilibrium with the weak acid [ce]HI3[/ce], so addition of protons will cause the equilibrium to shift such that more iodine dissolves in the water.