strip time to coat P 5 s Q 40 s R 3 min The diagram shows three metal strips in copper(II) sulfate solution, and the table gives the coating time. A shorter...
Question 1 Report
| strip | time to coat |
|---|---|
| P | 5 s |
| Q | 40 s |
| R | 3 min |
The diagram shows three metal strips in copper(II) sulfate solution, and the table gives the coating time. A shorter time means the strip metal is much more reactive than copper. Which strip is the most reactive?
Answer Details
A metal strip becomes coated with copper only if it is more reactive than copper, so it can push copper out of solution: \[\text{Cu}^{2+}(aq) + 2\text{e}^{-} \rightarrow \text{Cu}(s)\]
The bigger the reactivity gap, the faster the electrons are handed over and the sooner the brown copper layer appears. Strip P was coated in only 5 s, against 40 s for Q and a full 3 minutes for R, so P is the most reactive of the three.
The misconception here is to read a long coating time as a "bigger" reaction because more time passed. Time is an inverse measure: a short time means a fast reaction. In displacement experiments, quickest change equals greatest reactivity.
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