Question

A chemical reaction takes place when iron dust is added into copper sulphate solution, but no reaction takes place when copper dust is added into ferrous sulphate solution. Why?

Answer 1

Hint :On the basis of the reactivity of metals, metals are arranged in a series. The arrangement of metals is from highest to lowest reactivity. It helps to find the reactivity of metals with various acids, water etc. Reactivity series is also known as activity series.

Complete Step By Step Answer:
The series also helps us to predict whether a metal can displace another metal from its compound or not. If the metal is placed above another metal then only it can displace it from its compound in displacement reaction.
As iron is placed above copper in the series iron dust easily displaces copper from the sulphate and reaction happens.
 $ Fe + CuS{O_4} \to FeS{O_4} + Cu $
Whereas when copper dust is added to ferrous sulphate no reaction happens, as copper is not that much reactive to attract the anion present with iron (which so very much reactive).
 $ FeS{O_4} + Cu \to {\text{no reaction}} $
Hydrogen is also present in the series, metals that are above hydrogen can displace it from acids like HCl etc. and below cannot.

Note :
The reaction between copper sulphate and iron is single displacement reaction, the same happens when double displacement reaction occurs.Series also predict that the isolation of metals from its ore is difficult for higher metals and they need a large amount of energy for this. Higher metals are good reducing agents too as they easily lose electrons to oxidize themselves.