Question

If a spoon of copper metal is placed in a solution of ferrous sulphate, then ______.
A.Cu will precipitate out
B.Iron will precipitate out
C.Cu and Fe will precipitate
D.No reaction will take place

Answer 1

Hint: The relative activity of metals can be obtained from the electrochemical series by comparing their oxidation potentials. A metal with higher oxidation potential can displace metals with lower oxidation potentials from their corresponding salt solutions.

Complete step by step answer:
The standard electrode potentials of a large number of electrodes have been determined by using the standard hydrogen electrode as the reference electrode and its electrode potential has been fixed as zero arbitrarily. The electrode potentials of various electrodes are expressed as the reduction potentials with respect to the standard hydrogen electrode. The reduction potential is obtained from its oxidation potential by simply changing the sign.
The electrode at which the process of reduction takes place with respect to the standard hydrogen electrode has reduction potential which is given a positive sign and the electrode at which oxidation takes place with respect to the standard hydrogen electrode has a positive oxidation potential or has a reduction potential which is given a negative sign. The arrangement of these various electrodes in order of their increasing values of standard reduction potentials is called the electrochemical series. This series also includes in itself the activity series of metals. The electrochemical series can be used to compare the relative activities of metals. Higher the oxidation potential of a metal, more easily it can lose electrons and hence, greater is its reactivity. As a result, metals having greater oxidation potentials have the ability to displace metals having lower oxidation potentials from their salt solutions. From the electrochemical series, we can see that the standard oxidation potential of copper is \[ - 0.34{\text{V}}\] and that of iron is \[0.44{\text{V}}\]. Thus, the oxidation potentials of iron is greater than that of copper and so it can displace copper from its salt solution but copper cannot displace iron from its salt solution. Hence, no reaction will take place.

So the correct option is D.

Note:
The feasibility of the redox reaction can also be determined by calculating the EMF of the cell. If the EMF of the cell is positive, the reaction is feasible but if the EMF is negative, the reaction will not take place.
In this case, we need to check if the following reaction occur or not:
${\text{Cu + F}}{{\text{e}}^{{\text{2 + }}}} \to {\text{C}}{{\text{u}}^{2 + }}{\text{ + Fe}}$
The cell may be represented as ${\text{Cu}}\left| {{\text{C}}{{\text{u}}^{2 + }}} \right.\left\| {{\text{F}}{{\text{e}}^{2 + }}} \right.\left| {{\text{Fe}}} \right.$
So, oxidation is taking place at the copper electrode, it acts as anode and since reduction occurs at the iron electrode, it is the cathode.
The reduction potentials of copper anode and iron cathode are \[0.34{\text{V}}\] and \[ - 0.44{\text{V}}\] respectively.
Since, standard EMF of a cell is equal to difference between the standard reduction potentials of the cathode and the anode, so, the standard EMF of this cell is
$
   = - 0.44{\text{V}} - 0.34{\text{V}} \\
   = - 0.78{\text{V}} \\
 $
The EMF comes out to be negative and so, the reaction will not take place.