When `Cl_(2)` is passed through hot NaOH , oxidation number of Cl changes from

Options

A. `-1 " to " 0`
B. `0 " to " -1`
C. `0 " to " +5`
D. `0 " to " +7`

Answer

To determine the change in oxidation number of chlorine when \( Cl_2 \) is passed through hot sodium hydroxide (NaOH), we can analyze the reaction step by step.

### Step 1: Write the Reaction
When chlorine gas (\( Cl_2 \)) is passed through hot NaOH, the products formed are sodium chloride (\( NaCl \)) and sodium chlorate (\( NaClO_3 \)). The balanced chemical equation for this reaction is:

\[ Cl_2 + 2 NaOH \rightarrow NaCl + NaClO_3 + H_2O \]

### Step 2: Determine the Oxidation States
Next, we need to determine the oxidation states of chlorine in the reactants and products.

1. **In \( Cl_2 \)**: The oxidation state of chlorine is 0 (as it is in its elemental form).
2. **In \( NaCl \)**: The oxidation state of chlorine is -1. This can be calculated as follows:
- Sodium (Na) has an oxidation state of +1.
- Therefore, for \( NaCl \): \( +1 + x = 0 \) where \( x \) is the oxidation state of Cl. Thus, \( x = -1 \).

3. **In \( NaClO_3 \)**: The oxidation state of chlorine can be calculated using the known oxidation states of sodium and oxygen:
- Sodium (Na) has an oxidation state of +1.
- Oxygen (O) has an oxidation state of -2.
- For 3 oxygen atoms: \( 3 \times (-2) = -6 \).
- Therefore, for \( NaClO_3 \): \( +1 + x - 6 = 0 \) where \( x \) is the oxidation state of Cl. Thus, \( x = +5 \).

### Step 3: Analyze the Change in Oxidation State
Now we can summarize the changes in oxidation states:
- Chlorine changes from 0 in \( Cl_2 \) to -1 in \( NaCl \) (reduction).
- Chlorine changes from 0 in \( Cl_2 \) to +5 in \( NaClO_3 \) (oxidation).

### Step 4: Conclusion
Thus, the oxidation number of chlorine changes from 0 to -1 (reduction) and from 0 to +5 (oxidation). This indicates that both reduction and oxidation occur in this reaction, making it a redox reaction.

### Final Answer
The oxidation number of Cl changes from 0 to -1 in sodium chloride and from 0 to +5 in sodium chlorate.

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