Question

Consider the reactions:
a. `H_(3)PO_(2)(aq)+4AgNO_(3)(aq)+2H_(2)O(l) rarr H_(3)PO_(4)(aq)+4Ag(s)+4HNO_(3)(aq)`
b. `H_(3)PO_(2)(aq)+2CuSO_(4)(aq)+2H_(2)O(l) rarr H_(3)PO_(4)(aq)+2Cu(s)+H_(2)SO_(4)(aq)`
c. `C_(6)H_(5)CHO(l)+2[Ag(NH_(3))_(2)]^(o+)(aq)+3overset(Θ)(OH)(aq) rarr C_(6)H_(5)COO^(Θ)(aq)+2Ag(s)+4NH_(3)(aq)+2H_(2)O(l)`
d. `C_(6)H_(5)CHO(l)+2Cu^(2+)(aq)+5overset(Θ)(O)H(aq) rarr` No change observed
Wahat inference do you draw about the behaviour of `Ag^(o+)` and `Cu^(2+)` from these reaction?

Answer 1

Reactions `(a)` and `(b)` indicate that `H_(3)PO_(2)` (hypophosphorus acid) is a reducing agent and thus reduces both `AgNO_(3)` and `CuSO_(4)` to `Ag` and `Cu`, respectively. Conversely, both `AgNO_(3)` and `CuSO_(4)` act oxidising agent and thus oxidise `H_(3)PO_(2)` to `H_(3)PO_(3)` (phosphorus acid).
Reaction `(c )` suggests that `[Ag(NH_(3))_(2)]^(+)` oxidises `C_(6)H_(5)CHO` (benzaldehyde) to `C_(6)H_(5)COO^(Θ)` (benzotate ion), but reaction (d) indicates that `Cu^(2+)` ions cannot oxidise `C_(6)H_(5)CHO` to `C_(6)H_(5)COO^(Θ)`. Therefore, from the above reactions, we conclude that `Ag^(o+)` ion is a stronger oxidising agent than `Cu^(2+)` ion.