Simulation · Chemistry · Class 11

A metal strip in a salt solution

From the lesson Competitive electron transfer in Redox Reactions. Change the values and watch what happens.

The idea behind it

NCERT §7.2.1

A zinc strip dipped in copper nitrate solution for about an hour gets a reddish copper coating, and the blue of the solution fades: Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s). Zinc loses electrons to Cu²⁺.
The Zn²⁺ formed can be shown by passing H₂S through the colourless solution after making it ammoniacal: a white precipitate of ZnS appears.
A copper rod in zinc sulphate solution shows no change, and H₂S gives no black CuS. So Cu does not hand electrons to Zn²⁺; the reverse transfer does not occur.
Copper in silver nitrate solution does react: the solution turns blue as Cu²⁺ forms and silver is deposited, Cu(s) + 2Ag⁺(aq) → Cu²⁺(aq) + 2Ag(s).
The tendency to release electrons therefore falls in the order Zn > Cu > Ag. Arranging metals by this competition for electrons gives the metal activity series (electrochemical series).
In some pairs neither side wins completely. Cobalt in nickel sulphate solution reaches a state where both Co²⁺ and Ni²⁺ are present at moderate concentrations: the reaction reaches equilibrium.
The same competition, when the two half reactions are kept in separate beakers joined by a wire, can drive an electric current. This is the basis of a galvanic cell.

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