Question

Which of the following reactions is a Redox reaction? Cu(s) + 4HNO_3 rightarrow Cu(NO_3)_3 + 2 NO_2 + 2H_2O Cu(NO_3)_3 + 2 NaOH rightarrow Cu(OH)_2 + 2NaNO_3 Cu(OH)_2 + HCI rightarrow CuCl_2 + H_2O (a) (I) (b) (II) (c) (III) (d) All of them

Answer 1

Option (a) is correct one that means reaction (i) is a redox reaction whereas reaction (ii) and (iii) are double displacement reaction and neutralization reaction respectively.

(i) Cu⁰ (s) +4HN⁺⁵O₃   $\rightarrow$ Cu⁺²(NO₃)₂  + 2N⁺⁴O₂ + 2H₂O (Redox reaction where Cu is oxidised to Cu⁺² and N⁺⁵ is reduced to N⁺⁴.)

{ in the above question there must be a typing error because it is written as Cu(NO₃)₃ whereas it should be Cu(NO₃)₂ because oxidation states of Cu is +2 and +4]

In a redox reaction, there will be change of oxidation states and that does not happen in double replacement reaction and neutralization reaction (or acid -base reaction) so equation (ii) and (iii) are not redox reaction because there are no change in oxidation states of elements as shown below.

(ii) Cu⁺²(NO₃)₂ + 2Na⁺¹OH $\rightarrow$ Cu⁺²(OH)₂ + Na⁺¹NO₃ (Double displacement reaction)

{ in the above question there must be a typing error because it is written as Cu(NO₃)₃ whereas it should be Cu(NO₃)₂ because oxidation states of Cu is +2 and +4 }

(iiI) Cu⁺²(OH)₂  + 2HCl $\rightarrow$ Cu⁺²Cl₂  + 2H₂O   (neutralization reaction)

base acid salt water