Chemistry · Redox Equilibrium · NEET
The blue colour comes from Cu2+ ions in the solution. Zinc pushes electrons onto these Cu2+ ions, turning them into neutral copper metal (Cu2+ + 2e- to Cu). As Cu2+ ions leave the solution, the blue colour slowly disappears. At the same time Zn2+ ions enter the solution, but Zn2+ is colourless, so the solution becomes pale.
The copper that forms from Cu2+ ions deposits directly on the zinc surface as reddish metallic copper. So the zinc strip looks brown or reddish. Underneath, the zinc is slowly dissolving as Zn2+ ions, so the strip also gets thinner over time.
No. NCERT says if you place a copper strip in zinc sulphate solution, no visible reaction is seen and no Cu2+ ions form. Copper is less reactive than zinc, so copper cannot push electrons onto Zn2+. The reaction goes one way only: Zn + Cu2+ to Zn2+ + Cu.
Zinc loses electrons, so zinc is oxidised (it is the reducing agent). Copper ion gains those electrons, so Cu2+ is reduced (it is the oxidising agent). Use OIL RIG: Oxidation Is Loss, Reduction Is Gain. Zinc loses, copper ion gains.
Both zinc and copper 'compete' to hold electrons. Zinc has a stronger tendency to give up electrons than copper, so zinc wins by handing electrons to Cu2+. The metal that gives electrons more easily (higher in the reactivity series) always wins the competition.
Which of the following reactions is a metal displacement reaction? Choose the right option.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Zn(s) + CuSO4(aq) to ZnSO4(aq) + Cu(s). In ionic form: Zn(s) + Cu2+(aq) to Zn2+(aq) + Cu(s). Zinc is oxidised and copper ion is reduced.
It is both. It is a metal displacement reaction, and because electrons are transferred (oxidation number of Zn goes 0 to +2, and Cu goes +2 to 0), it is also a redox reaction.
Cu2+ is the oxidising agent because it accepts electrons and gets reduced. Zinc is the reducing agent because it donates electrons and gets oxidised.
NCERT notes that heat is evolved during this direct electron transfer. The reaction is exothermic, so the beaker gets slightly warm.
The Daniell cell uses this same Zn + Cu2+ reaction, but separates the two half-reactions into two beakers joined by a salt bridge, so the electrons flow through a wire and produce electricity instead of heat.
