Balancing A Redox Reaction

Concept: Chemistry (Redox Reactions) - Oxidizing Agents and Electron Transfer.

Step 1: Determine the oxidation states of the elements. In the reactants: Solid zinc ( ) is in its elemental state, so its oxidation number is 0. In , hydrogen is and chlorine is . In the products: In zinc chloride ( ), zinc is and chlorine remains . Hydrogen gas ( ) is elemental, so its oxidation number is 0.

Step 2: Identify the oxidation and reduction half-reactions. Oxidation (loss of electrons): Zinc's oxidation state increases from 0 to . The half-reaction is . Reduction (gain of electrons): Hydrogen's oxidation state decreases from to 0. The half-reaction is .

Step 3: Identify the oxidizing agent. An oxidizing agent is the substance that gets reduced (gains electrons) and causes the oxidation of another substance. Since the ions in are gaining electrons and being reduced to , is the oxidizing agent.

Step 4: Analyze the electron transfer per mole of the reaction. From the balanced overall equation and the reduction half-reaction , we can see that it requires exactly 2 moles of electrons to reduce 2 moles of .

Step 5: Calculate the electron gain for ONE mole of the oxidizing agent. The question specifically asks for the number of moles of electrons gained by exactly ONE mole of the oxidizing agent. Since 2 moles of gain 2 moles of electrons, we divide by 2. Therefore, 1 mole of gains mole of electrons. $ $

In a redox reaction, oxidation is the loss of electrons. In the given reaction: Zinc loses electrons and is thus oxidized. Copper ions gain electrons and are reduced.

In , the oxygen atoms have an oxidation state of -2. Since the compound is neutral, the total oxidation state must be zero. Let the oxidation state of chlorine be . The total oxidation state is: Therefore, the oxidation state of chlorine in is +7. So, the correct answer is option (1).