Q20E - Chemistry (OpenStax)

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

Step-by-Step Solution

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 1: 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.

Step 2: 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.

Step 3: 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.

Step 4: 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.

Step 5: 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.

Step 6: 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.