posted by Caileen .
Is there a reaction between CuSO4 + KI? When I performed the reaction, a brown and yellow color was formed but when I wrote out the molecular equation, I did not find a precipitate or gas evolution.
but why is there a reaction?
Its a redox reaction. The Cu^+2 is reduced to Cu^+1 and the I^- is oxidized to I2. Oxidation/reduction reactions take place if the potential of the cell produced is a positive voltage. The potential created by the reduction of Cu + the potential created by the oxidation of I2 is a positive voltage.
The reaction is
2Cu^+2(aq) + 4I^-(aq) ==> 2CuI(s) + I2
The yellow-brown color you saw was the I2. USUALLY that is so dark you can't see through the solution; however, I suspect you did not have a high excess of KI AND it wasn't acid enough so you only had a small amount of I2 produced.