Question

What element is being reduced in the following (unbalanced) redox reaction, which occurs in acid?

Ag(s) + CN^-(aq) + O₂(g) --> Ag(CN)₂^- (aq) + H₂O(l)

C

O

Ag

N

K

Answer 1

To determine which element is being reduced in a redox reaction, we need to compare the oxidation states of the elements in the reactants and products. The element that undergoes a decrease in oxidation state is being reduced.

In the given reaction: Ag(s) + CN-(aq) + O2(g) → Ag(CN)2-(aq) + H2O(l)

Let's assign oxidation states to the elements involved:

Ag(s): The oxidation state of Ag in its elemental form is 0.

CN-(aq): The oxidation state of C in CN- is -1, and the oxidation state of N in CN- is -3.

O2(g): Oxygen in O2 typically has an oxidation state of 0.

Ag(CN)2-(aq): The oxidation state of Ag in Ag(CN)2- is +1, the oxidation state of C in CN- is -1, and the oxidation state of N in CN- is -3.

H2O(l): The oxidation state of H in H2O is +1, and the oxidation state of O in H2O is -2.

From the assigned oxidation states, we can observe that the oxidation state of Ag changes from 0 in Ag(s) to +1 in Ag(CN)2-(aq). It undergoes an increase in oxidation state, indicating that Ag is being oxidized.

Since Ag is being oxidized, the element being reduced in the reaction is O. Oxygen in O2(g) has an oxidation state of 0, and in H2O(l), it has an oxidation state of -2. Thus, oxygen is being reduced from an oxidation state of 0 to -2.

Therefore, the element being reduced in the given redox reaction is oxygen (O).