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"When a zinc plate placed in copper sulphate solutionfor some time,after sometime we can see holes in plate , why?"

So this was a question in my book , I don't want answer of this one.

But I Want answer of this one:-

Does displacement reaction only take place on surface of any metal plate ( high reactive)? Beacuse we heard 'deposit' word , like copper deposited on zinc. So I zinc from surface of plate started dissolving and in place of zinc , copper deposit on that plate. So I think reaction should stop after all surface zinc has been displaced by copper, beacuse now it is covered by copper and solution has ZnSO4 . Than why hole get build in plate , does inner zinc also taking part in displacement reaction?

Why if copper is already deposit on surface(surface zinc should have start dissolving first and copper simultaneously cover the surface of plate)

Also according to above , some CuSO4 should still left in solution along with ZnSO4 , as inner (zinc under copper deposit on zinc plate ) hasn't displaced.

This make sense because if whole zinc plate has been dissolved than copper from solution just don't get place to deposit and settle like sand at bottom?

Please clear my doubts,

Does only surface of a metal plate(high reactive) take part in displacement reaction ? (And remaining metal plate under deposited layer of less reactive metal remain undissolved) If yes than why holes build in plate?why does layer deposit on plate protect inner metal from further dissolving. If you want any clarification, please let me know but don't mark my question negative If u think deeply it is a good question.

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Copper deposited on the zinc surface does not protect the remaining zinc to be dissolved. Copper does not form a real layer on the zinc surface. As long as some metallic zinc remains in contact of the copper sulfate solution, the reaction will proceed. It may be irregular and produce holes in the zinc plate. The reaction will stop when and only when the zinc metal or the copper solution is missing

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  • $\begingroup$ Thank u....so much . So u mean even after copper layer is formed on zinc , it will still cause dissolving of inner Zinc 🤔 ? And what do u mean "when zinc metal missing" , do u mean when it is fully covered with Copper or do u mean all zinc got dissolve? And why that holes appear in plate of zinc? $\endgroup$
    – Suresh Chandra Pal
    Commented Sep 16, 2021 at 13:59
  • $\begingroup$ U said "as long as some metallic zinc remain in contact with cuso4" , that i am asking ....suppose outer surface zinc will start displacing copper and after some time cu will form a covering on zinc metal. Than why it is said we will see holes in zinc plate after some time . It is like saying " zinc is keep dissolving until it created hole in plate " where does cu went , it should deposit on plate after "Surface" zinc has replaced Cu from CuSO4 , and protect inner zinc .....just like galvanisation( just analogy i know they are 2 different things but zinc protect inner metal from corrosion ) $\endgroup$
    – Suresh Chandra Pal
    Commented Sep 16, 2021 at 14:04
  • $\begingroup$ Copper will never form a covering on zinc. The copper deposit does not adhere on the zinc plate. It looks like moss or foam. Copper and zinc do not have the same density. The copper layer does not hold on the zinc. As long as the reaction proceeds, the amount of metallic zinc decreases. The copper does not protect the zinc. The zinc plate becomes thinner and thinner. The amount of copper becomes more and more important. After some time, there is no metallic zinc any more. But before, holes may appear in the zinc plates, depending on the currents in the solution. $\endgroup$
    – Maurice
    Commented Sep 16, 2021 at 15:39
  • $\begingroup$ So u mean covering is not like a sticky ....I mean eg. Paint on a iron rod, so covering is not like that, instead it is foam like? And zinc will keep decreasing? $\endgroup$
    – Suresh Chandra Pal
    Commented Sep 17, 2021 at 5:22
  • $\begingroup$ Yes. When a new $\ce{Zn^{2+}}$ is created it needs room to be dissolved in water. It repells the newly created copper atom away from the metallic surface. And zinc keeps decreasing $\endgroup$
    – Maurice
    Commented Sep 17, 2021 at 7:33

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