The change in the oxidation state of iodine when axcess chlorine water is added to an iodide salt is

Answer

To solve the problem of determining the change in oxidation state of iodine when excess chlorine water is added to an iodide salt, we can follow these steps:

### Step 1: Identify the iodide salt
The iodide salt mentioned in the question is potassium iodide (KI). In this compound, iodine has an oxidation state of -1.

### Step 2: Write the reaction with chlorine
When excess chlorine water (Cl2) is added to potassium iodide, a reaction occurs where chlorine displaces iodine. The balanced chemical equation for this reaction is:
\[ 2 \text{KI} + \text{Cl}_2 \rightarrow 2 \text{KCl} + \text{I}_2 \]
In this reaction, iodine (I) is oxidized from -1 in KI to 0 in I2.

### Step 3: Determine the oxidation state of iodine in I2
In the diatomic molecule I2, the oxidation state of iodine is 0 because it is in its elemental form.

### Step 4: Analyze the further reaction with chlorine water
The iodine produced (I2) will then react with chlorine water. The balanced equation for this reaction is:
\[ 5 \text{Cl}_2 + \text{I}_2 + 6 \text{H}_2\text{O} \rightarrow 2 \text{HIO}_3 + 10 \text{HCl} \]
In this reaction, iodine is further oxidized to iodic acid (HIO3).

### Step 5: Determine the oxidation state of iodine in HIO3
To find the oxidation state of iodine in HIO3, we can set up the equation based on the known oxidation states of hydrogen and oxygen:
- Let the oxidation state of iodine be \( x \).
- The oxidation state of hydrogen is +1 (2 hydrogen atoms contribute +2).
- The oxidation state of oxygen is -2 (3 oxygen atoms contribute -6).

Setting up the equation:
\[ x + 2 + (-6) = 0 \]
Solving for \( x \):
\[ x - 4 = 0 \implies x = +5 \]
Thus, the oxidation state of iodine in HIO3 is +5.

### Step 6: Calculate the change in oxidation state
Now we can calculate the change in oxidation state of iodine:
- Initial oxidation state in KI: -1
- Final oxidation state in HIO3: +5

The change in oxidation state is:
\[ +5 - (-1) = +5 + 1 = +6 \]

### Conclusion
The overall change in the oxidation state of iodine when excess chlorine water is added to an iodide salt is +6.

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