Copper sulfate, when it is dissolved in water, has a blue color. When steel wool is mixed with a copper sulfate solution, the steel wool disappears, a brownish solid forms, and the color of the solution changes from blue to green. Choose one answer that gives the best evidence that a chemical reaction took place.

A. The color change from blue to green happens in nature.

B. The disappearance of the steel wool shows that a new substance has formed.

C. The solid precipitate is a waste product in the reaction.

D. Energy is lost in this reaction like all other reactions.

Which answer did you choose? Explain your reasoning.

The evidence that shows that a chemical reaction has taken place is the disappearance of the steel wool shows that a new substance has formed.

The electrochemical series is arrangement of elements in order of decreasing reactivity. It is important to note that the elements that are high up in the electrochemical series can displace the elements that are lower in the series from their aqueous solution.

Steel contains iron which lies above copper in the electrochemical series hence a chemical change occurs when steel dissolves in the copper solution.

Hence, the evidence that shows that a chemical reaction has taken place is the disappearance of the steel wool shows that a new substance has formed.

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A. The color change from blue to green happens in nature.

Explanation:

The color change is an indicator of a chemical reaction that has occurred. Although color changes are not necessarily good diagnostic tool to measure if a chemical reaction has occurred or not.