3. What evidence is there for a chemical reaction when the two solutions are mixed?

When the solution of KSCN is added to the solution Fe(NO3)3 a reaction occurs. We conclude a reaction has occurred because the solution, which were initially a pale yellow and colorless, turned a reddish-brown color upon mixing. No precipitate is evident. Only a solution with the new color. The product of the reaction is soluble, but also is colored. We've seen solutions that are colored like this before. For example; solution containing Cu2+ are bluish green, solutions containing Ni2+ are green. Both of these examples the ion that imparts color to the solution is a transition metal.

In the reaction we are looking at the reactants are;

Fe3+(aq) + SCN-(aq) --->

Before mixing the Fe3+(aq) solution is a yellowish in color. After adding the SCN-(aq) the solution changes color to the reddish-brown. The product turns out to be best described as a 'complex ion' which in this case means a substance with one Fe3+ ion and one SCN-ion. The formula of the product is FeSCN2+(aq).