The question is: Is the blue chemical in the copper sulfate solution a catalyst? How do you know?I don't understand this because copper sulfate itself is blue.
Copper ions in solution are blue. If you add steel(iron) or zinc to a copper sulfate solution, the copper ions will take electrons off (oxidize) the more reactive metal, and become copper metal (coating the iron or zinc, and/or precipitating to the bottom of the solution) and as this metal displacement reaction proceeds, the blueness of the copper sulfate solution will fade, as there will be fewer Cu2+ ions remaining in the solution.
