Question

Identify the atoms that are oxidized and reduced, the change in the oxidation state for each, and the oxidizing and reducing agents in each of the following equations:

(a)\(Mg\left( s \right) + NiC{l_2}\left( {aq} \right) \to MgC{l_2}\left( {aq} \right) + Ni\left( s \right)\)

(b)\(PC{l_3}\left( l \right) + C{l_2}\left( g \right) \to PC{l_5}\left( s \right)\)

(c)\({C_2}{H_4}\left( g \right) + 3{O_2}\left( g \right) \to 2C{O_2}\left( g \right) + 2{H_2}O\left( g \right)\)

(d)\(Zn\left( s \right) + {H_2}S{O_4}\left( {aq} \right) \to ZnS{O_4}\left( {aq} \right) + {H_2}\left( g \right)\)

(e) \(2{K_2}{S_2}{O_3}\left( s \right) + {I_2}\left( s \right) \to {K_2}{S_4}{O_6}\left( s \right) + 2KI\left( s \right)\)

(f) \(3Cu\left( s \right) + 8HN{O_3}\left( {aq} \right) \to 3Cu{\left( {N{O_3}} \right)_2}\left( {aq} \right) + 2NO\left( g \right) + 4{H_2}O\left( l \right)\)

Short answer

(a) Mg is oxidised and Ni is reduced,change in oxidation state -Mg (0 to +2) andNi (+2 to 0), Mg is reducing agent and Ni is oxidising agent.

(b) P is oxidised and Cl is reduced, change in oxidation state - P (+3 to +5) and Cl (0 to -1), P is reducing agent and Cl is oxidising agent

(c) C is oxidised and O is reduced, change in oxidation state- C (-2 to +4) and O (0 to -2), C is reducing agent and O is oxidising agent.

(d) Zn is oxidised and H is reduced, change in oxidation state-Zn(0 to +2)and H(+1 to 0), Zn is reducing agent and H is oxidising agent

(e) S is oxidised and I is reduced,change in oxidation state- S(+2 to +2.5) and I (0 to -2), S is reducing agent and I is oxidising agent

(f) Cu is oxidised and N is reduced, change in oxidation state-Cu (0 to +2) and N (+5 to +3), Cu is reducing agent and N is oxidising agent

Step-by-step solution

Consider the reaction (a)

\(Mg\left( s \right) + NiC{l_2}\left( {aq} \right) \to MgC{l_2}\left( {aq} \right) + Ni\left( s \right)\)

Here magnesium is oxidised, hence it is the reducing agent, whereas nickel is reduced, making it the oxidising agent. The change in oxidation state of magnesium is from 0 to +2 and nickel is from +2 to 0.

Consider the reaction (b)

\(PC{l_3}\left( l \right) + C{l_2}\left( g \right) \to PC{l_5}\left( s \right)\)

Here phosphorus is oxidised, hence it is the reducing agent, while chlorine is reduced, making it the oxidising agent.The change in oxidation state of phosphorus is from +3 to +5 and chlorine is from 0 to -1.

Consider the reaction (c)

\({C_2}{H_4}\left( g \right) + 3{O_2}\left( g \right) \to 2C{O_2}\left( g \right) + 2{H_2}O\left( g \right)\)

Here carbon is oxidised, hence it is the reducing agent, while oxygen is reduced, making it the oxidising agent.The change in oxidation state of carbon is from -2 to +4 and oxygen is from 0 to -2.

Consider the reaction (d)

\(Zn\left( s \right) + {H_2}S{O_4}\left( {aq} \right) \to ZnS{O_4}\left( {aq} \right) + {H_2}\left( g \right)\)

Here zinc is oxidised, hence it is the reducing agent, while hydrogen is reduced, making it the oxidising agent.The change in oxidation state of zinc is from 0 to +2 and hydrogen is from +1 to 0.

Consider the reaction (e)

\(2{K_2}{S_2}{O_3}\left( s \right) + {I_2}\left( s \right) \to {K_2}{S_4}{O_6}\left( s \right) + 2KI\left( s \right)\)

Here sulfur is oxidised, hence it is the reducing agent, while iodine is reduced, making it the oxidising agent.The change in oxidation state of sulphur is from +2 to +2.5 and iodine is from 0 to -2.

Consider the reaction (f)

\(3Cu\left( s \right) + 8HN{O_3}\left( {aq} \right) \to 3Cu{\left( {N{O_3}} \right)_2}\left( {aq} \right) + 2NO\left( g \right) + 4{H_2}O\left( l \right)\)

Here copper is oxidised, hence it is the reducing agent, while nitrogen is reduced, making it the oxidising agent.The change in oxidation state of copper is from 0 to +2 and nitrogen is from +5 to +3.