8.11. Whenever a reaction between an oxidising agent and a reducing agent is carried out, a compound of lower oxidation state is formed if the reducing agent is in excess and a compound of higher oxidation state is formed if oxidising agent is in excess. Justify this statement giving three illustrations.

<p>The three examples are:</p><p><strong> (i)</strong> When excess&nbsp;P_4?&nbsp; (reducing agent) reacts with&nbsp;F_2? (oxidizing agent), &nbsp;PF_3?&nbsp;is produced in which P has +3 oxidation number.<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; P_4? (excess)&nbsp;+ F₂? → PF₃? <br>But if fluorine is in excess, &nbsp;PF₅? &nbsp;is formed in which P has oxidation number of +5.<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; P_4?? + F₂? (excess)&nbsp;→ PF₅? <br><br><strong> (ii)</strong> Oxidizing agent is oxygen and reducing agent is K. When excess K reacts with oxygen, &nbsp;K_2?O&nbsp;is formed in which oxygen has oxidation number of -2.<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 4K (excess)&nbsp;+ O₂? → 2K₂? O<br><br>But if oxygen is in excess, then&nbsp;K_2?O₂? &nbsp;is formed in which O has oxidation number of -1.<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 2K + O₂? (excess)&nbsp;→ K₂? O₂? <br><br><strong> (iii)</strong> The oxidizing agent is oxygen and the reducing agent is C. When an excess of C reacts with oxygen, CO is formed in which C has +2 oxidation number.<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; C (excess)&nbsp;+ O_2? → CO<br><br>When excess of oxygen is used, &nbsp;CO₂? &nbsp;is formed in which C has +4 oxidation number.<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; C + O₂? (excess)&nbsp;→ CO₂</p>

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