A student did experiments to establish the relative reactivity of metallic Zn, C

Question

A student did experiments to establish the relative reactivity of metallic Zn, Cu, and Pb. The following observations were made: (a) both Zn and Pb metals reacted with 6M HCl, but Cu metal did not; (b) there was no reaction between lead (II) sulfate solution (PbSO_4) and Cu metal, but there was a reaction between PbSO_4 solution and Zn metal. (1) Write chemical equations based on each of the observations in (a) above. (2) Write chemical equations describing the observations in (b). (3) List the three metals and hydrogen in order of relative reactivity.

Explanation / Answer

Ans 3

The simple reason of the reactivity of metals in a reaction is their order or position in the reactivity table .

a) Zinc and Lead reacts with HCl as following

Zn + 2HCl = ZnCl2 + H2

Pb + 2HCl = PbCl2 + H2

Both Zn and Pb have negative stanadard reduction potential of -0.76 V and -0.13V , so they are able to reduce hydrogen from its acid .

Copper has positive standard reduction potential of +0.34 V , hence it cannot reduce Hydrogen from HCl.

b)

lead sulfate reacts with zinc to produce lead and zinc sulfate according to the reaction

PbSO4 + Zn = ZnSO4 + Pb

So Zn has more negative reduction potential than Pb so it can replace it from its solution .

But Copper as it has positive reduction potential as compared to Pb , cannot replace Pb from PbSO4

c) So the order of reactivity according to the standard electrode potentials from lower to higher is:

Copper < Hydrogen < lead < Zinc

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