Question

Why does the blue colour of copper sulphate solution get discharged when zinc rod is dipped into it?

Given: \[\ce{E^{\circ}_{Cu^{2+}/Cu}}\] = +0.34 V and \[\ce{E^{\circ}_{Zn^{2+}/Zn}}\] = −0.76 V.

Answer 1

The blue colour of copper sulphate solution fades when a zinc rod is dipped into it because of a redox reaction where zinc displaces copper from the solution.

The standard reduction potential of zinc is lower than that of copper.

\[\ce{E^{\circ}_{Zn^{2+}/Zn}}\] = −0.76 V (Stronger reducing agent)

\[\ce{E^{\circ}_{Cu^{2+}/Cu}}\] = +0.34 V

Because zinc is more reactive (i.e., has a lower reduction potential), it oxidises more easily than copper.

The reaction occurs is \[\ce{Zn_{(s)} + Cu{^{2+}_{(aq)}} -> Zn{^{2+}_{(aq)}} + Cu_{(s)}}\]

Zinc atoms lose electrons (oxidation) and go into the solution as Zn²⁺.

Cu²⁺ ions in the blue solution gain electrons (reduction) and deposit as reddish-brown solid copper.