The order of intensity of reactivity of metals is known as reactivity series of metals. Reactivity of metals decreases on moving from top to bottom in the given series. This means that the most reactive metal is at the top while the least reactive one is at the bottom.
You will notice that copper, gold, and silver are at the bottom of the reactivity series because these are the least reactive metals. These metals are known as noble metals, because they are almost un-reactive. You will notice that potassium and sodium are at the top of the reactivity series. These metals are highly reactive. Remaining metals are moderately reactive.
Reactivity of some metals are given in descending order
You must have read about displacement reaction in chapter on Chemical Reaction and Equations. You may reacll that when a more reactive metal reacts with the salt solution of a less reactive metal, it displaces the less reactive metal from the salt to make its own salt. This is called displacment reaction. General equation for displacement reaction is given below.
Metal A + Salt of metal B ⇨ Salt of metal A + Metal B
Fig Ref: NCERT Textbook Class 10 Science
The reaction between iron and solution of copper sulphate is probably the most famous reaction to illustrate displacement reaction. You may have come across this example in previous classes as well. The colour of copper sulphate solution is blue. What happens when iron nail, or iron blade is kept immersed in copper sulphate solution? Most of you will quickly reply that the blue colour of copper sulphate fades away and is replaced by light green colour. Why does this happen? This happens because iron (being more reactive than copper) displaces copper from copper sulphate solution, and makes iron sulphate. The colour of iron sulphate solution is light green. This is a classical example of displacement reaction.
Fe + CuSO4 ⇨ FeSO4 + Cu
Aluminium and zinc are more reactive than copper. So, aluminium and zinc displace copper from the solution of copper sulphate. Following are equations for these reactions. In these reactions, aluminium sulphate and zinc sulphate are formed in that order.
2Al + 3CuSO4 ⇨ Al2(SO4 )3 + 3Cu
Zn + CuSO4 ⇨ ZnSO4 + Cu
In above examples, iron, aluminium and zinc are more reactive than copper. That's why they displace copper from its salt solution.
Copper is more reactive than silver nitrate. So, when copper is dipped in solution of silver nitrate, it displaces silver and forms copper nitrate. Following equation shows this reaction.
Cu + 2AgNO3 + Cu(NO3 )2 + 2Ag
But what happens when silver is kept in copper sulphate solution? Silver is less reactive than copper. So, silver does not react with copper sulphate solution. In this case, no reaction takes place.
Ag + CuSO4 ⇨ No reaction
What happens when gold is dipped in copper sulphate solution? Gold is less reactive than copper. So, when gold is dipped in the solution of copper sulphate, no reaction takes place. Gold cannot displace copper from copper sulphate.
Au + CuSO4 ⇨ No reaction
What happens when copper is dipped in aluminium nitrate solution. You can refer to reactivity series to get an answer. Copper is less reactive than aluminium. So, no reaction takes place when copper is dipped in the solution of aluminium nitrate. Copper cannot displace aluminium from aluminium nitrate.
Al(NO3 )3 + Cu ⇨ No reaction
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