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.
answered above.
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.
To determine if a reaction occurs between CuSO4 (copper(II) sulfate) and KI (potassium iodide), we can write out the balanced molecular equation for the reaction and examine the products.
The chemical formula for copper(II) sulfate is CuSO4, and that for potassium iodide is KI. The balanced molecular equation for the reaction can be written as follows:
CuSO4 + 2KI -> CuI2 + K2SO4
In this reaction, copper(II) sulfate reacts with potassium iodide to yield copper(II) iodide (a yellow compound) and potassium sulfate (a colorless compound).
Since copper(II) iodide is a yellow compound, it may explain the yellow color you observed. The brown color could be due to impurities or other factors unrelated to the reaction.
Although the balanced molecular equation does not show the formation of a precipitate or gas evolution, it is important to note that not all chemical reactions result in these observable changes. In some cases, reactions may involve color changes or the formation of soluble compounds that do not precipitate.
Experiments should be performed carefully, considering factors such as temperature, concentration, and the presence of catalysts, as these can influence the outcome of a reaction. Additionally, confirming the reaction products through additional tests or analysis techniques can provide more conclusive evidence of the reaction.