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

Answer

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

### Step-by-Step Solution:

1. **Identify the Initial Oxidation State of Iodine:**
- In an iodide salt like KI (potassium iodide), iodine has an oxidation state of -1.

2. **Reaction with Chlorine Water:**
- When excess chlorine water (Cl2) is added to KI, a reaction occurs:
\[ 2KI + Cl_2 \rightarrow 2KCl + I_2 \]
- In this reaction, iodine (I) is oxidized from -1 to 0 (as it forms I2).

3. **Further Reaction of Iodine with Chlorine:**
- The remaining iodine (I2) can react with chlorine in the presence of water:
\[ I_2 + 6H_2O + 5Cl_2 \rightarrow 10HCl + 2HIO_3 \]
- In this reaction, we need to find the oxidation state of iodine in HIO3.

4. **Determine the Oxidation State of Iodine in HIO3:**
- In HIO3, we can set up the equation for the oxidation state of iodine (let's denote it as x):
\[ x + 1 + 3(-2) = 0 \]
- Simplifying this gives:
\[ x + 1 - 6 = 0 \implies x - 5 = 0 \implies x = +5 \]
- Thus, the oxidation state of iodine in HIO3 is +5.

5. **Calculate the Change in Oxidation State:**
- The change in oxidation state of iodine when moving from -1 (in KI) to +5 (in HIO3) is calculated as follows:
\[ \text{Change} = +5 - (-1) = +5 + 1 = +6 \]

### Final Answer:
The change in the oxidation state of iodine when excess chlorine water is added to an iodide salt is **+6**.