Question

Which of the following reactions are redox reactions? Which of the following reactions are redox reactions? Ca(s)+Cl2(g)→CaCl2(s) HCl(aq)+NaOH(aq)→H2O(l)+NaCl(aq) Zn(s)+Fe2+(aq)→Zn2+(aq)+Fe(s) Ba(NO3)2(aq)+K2SO4(aq)→BaSO4(s)+2KNO3(aq)

Answer 1

Answer :  The redox reactions are:

$Ca(s)+Cl_2(g)\rightarrow CaCl_2(s)$

$Zn(s)+Fe^{2+}(aq)\rightarrow Zn^{2+}(aq)+Fe(s)$

Explanation :

Redox reaction or Oxidation-reduction reaction : It is defined as the reaction in which the oxidation and reduction reaction takes place simultaneously.

Oxidation reaction : It is defined as the reaction in which a substance looses its electrons. In this, oxidation state of an element increases. Or we can say that in oxidation, the loss of electrons takes place.

Reduction reaction : It is defined as the reaction in which a substance gains electrons. In this, oxidation state of an element decreases. Or we can say that in reduction, the gain of electrons takes place.

(1) $Ca(s)+Cl_2(g)\rightarrow CaCl_2(s)$

This reaction is a redox reaction.

In this reaction, the oxidation state of 'Ca' changes from (0) to (+2) that means 'Ca' lost 2 electrons and it shows oxidation reaction and the oxidation state of 'Cl' changes from (0) to (-1) that means 'Cl' gain 1 electron and it shows reduction reaction.

(2) $HCl(aq)+NaOH(aq)\rightarrow H_2O(l)+NaCl(aq)$

This reaction is a double-displacement reaction in which the cation of two reactants molecule exchange their places to give two different products.

In double-displacement reaction, the oxidation state of cation and anion remains same on both side of the reaction. So, it is not a redox reaction.

(3) $Zn(s)+Fe^{2+}(aq)\rightarrow Zn^{2+}(aq)+Fe(s)$

This reaction is a redox reaction.

In this reaction, the oxidation state of 'Zn' changes from (0) to (+2) that means 'Zn' lost 2 electrons and it shows oxidation reaction and the oxidation state of 'Fe' changes from (+2) to (0) that means 'Fe' gain 2 electron and it shows reduction reaction.

(4) $Ba(NO_3)_2(aq)+K_2SO_4(aq)\rightarrow BaSO_4(s)+2KNO_3(aq)$

This reaction is a double-displacement reaction in which the cation of two reactants molecule exchange their places to give two different products.

In double-displacement reaction, the oxidation state of cation and anion remains same on both side of the reaction. So, it is not a redox reaction.