In iodometric titrations, an oxidizing agent such as `KNnO_(4), K_(2)Cr_(2)O_(7),CuSO_(4),H_(2)O_(2)` is allowed to react in neutral medium or in acidic medium with excess of potassium iodide to liberate free iodine `Kl+` oxidizon agent `to l_(2)`
Free iodine is titrated against stanard reducing agent usually with sodium thiosulphate i.e.,
`K_(2)Cr_(2)O_(7)+6Kl+7H_(2)SO_(4)toCr_(2)(SO_(4))_(3)+4K_(2)SO_(4)+7H_(2)O+l_(2)`
`2CuSO_(4)+4Kl to Cu_(2)l_(2)+2K_(2)SO_(4)+l_(2)`
`l_(2)+Na_(2)S_(2)O_(3)to 2Nal+Na_(2)S_(4)O_(6)`
In iodometric titrations, starch solution is used as an indicator. Starch solution gives blue or violet colour with free iodine. At the end point, blue or violet colour disappear when iodine is completely changed to iodide.
A `1.1g` sample of copper ore is dissovled and `Cu^(2+)` (aq.) is treated with `Kl.l_(2)` liberated required `12.12mL` of `0.1M Na_(2)S_(2)O_(3)` solution for titration. The `% Cu` in the ore in the ore is:

Options

A. `2.5%`
B. `7%`
C. `5.8%`
D. `4.2%`

Explanation

To solve the problem of determining the percentage of copper in the copper ore sample, we will follow these steps:

### Step 1: Calculate the milli-equivalents of sodium thiosulfate (Na₂S₂O₃)

The formula for calculating milli-equivalents is:
\[ \text{milli-equivalents} = \text{molarity} \times \text{volume (mL)} \]
Given:
- Molarity of Na₂S₂O₃ = 0.1 M
- Volume of Na₂S₂O₃ used = 12.12 mL

Calculating the milli-equivalents:
\[ \text{milli-equivalents of Na₂S₂O₃} = 0.1 \, \text{mol/L} \times 12.12 \, \text{mL} = 1.212 \, \text{milli-equivalents} \]

### Step 2: Relate milli-equivalents of sodium thiosulfate to copper (Cu²⁺)

In iodometric titrations, the milli-equivalents of sodium thiosulfate will equal the milli-equivalents of copper ions:
\[ \text{milli-equivalents of Cu}^{2+} = \text{milli-equivalents of Na}_2\text{S}_2\text{O}_3 \]
Thus,
\[ \text{milli-equivalents of Cu}^{2+} = 1.212 \, \text{milli-equivalents} \]

### Step 3: Calculate the weight of copper in the sample

The formula for calculating the weight of copper from milli-equivalents is:
\[ \text{milli-equivalents} = \frac{\text{weight of Cu (g)}}{\text{molar mass of Cu (g/mol)} \times \text{valency}} \times 1000 \]
For copper, the molar mass is 63.5 g/mol and the valency is 2. Rearranging the formula to find the weight of copper:
\[ \text{weight of Cu} = \text{milli-equivalents} \times \frac{\text{molar mass of Cu}}{\text{valency}} \times \frac{1}{1000} \]
Substituting the values:
\[ \text{weight of Cu} = 1.212 \times \frac{63.5}{2} \times \frac{1}{1000} = 0.0768 \, \text{g} \]

### Step 4: Calculate the percentage of copper in the ore sample

Now, we can calculate the percentage of copper in the ore sample:
\[ \text{Percentage of Cu} = \left( \frac{\text{weight of Cu}}{\text{weight of sample}} \right) \times 100 \]
Given the weight of the sample is 1.1 g:
\[ \text{Percentage of Cu} = \left( \frac{0.0768}{1.1} \right) \times 100 \approx 6.98\% \]

### Final Answer
The percentage of copper in the ore sample is approximately **7%**.

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