Which of the following compounds is used as the starting material for the preparation of potassium dichromate?

Options

A. `K_2SO_4Cr_2(SO_4)_324H_2O` (Chrome alum)
B. `Pb CrO_4` (Chromite yellow)
C. `FeCr_2O_4` (Chromite)
D. `PbCrO_4PbO` (Chrome red)

Answer

To determine which compound is used as the starting material for the preparation of potassium dichromate, we can follow these steps:

### Step 1: Identify the Starting Material
The preparation of potassium dichromate begins with chromite ore, which is represented by the chemical formula FeCr2O4.

### Step 2: Reaction with Sodium Carbonate
The first step in the preparation process involves reacting chromite ore (FeCr2O4) with sodium carbonate (Na2CO3) in the presence of oxygen (O2). This reaction produces sodium chromate (Na2CrO4), iron oxide (Fe2O3), and carbon dioxide (CO2).

**Reaction:**
\[ \text{FeCr}_2\text{O}_4 + \text{Na}_2\text{CO}_3 + \text{O}_2 \rightarrow \text{Na}_2\text{CrO}_4 + \text{Fe}_2\text{O}_3 + \text{CO}_2 \]

### Step 3: Formation of Sodium Dichromate
In the second step, sodium chromate (Na2CrO4) is reacted with sulfuric acid (H2SO4). This reaction yields sodium dichromate (Na2Cr2O7), sodium sulfate (Na2SO4), and water (H2O).

**Reaction:**
\[ \text{Na}_2\text{CrO}_4 + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{Cr}_2\text{O}_7 + \text{Na}_2\text{SO}_4 + \text{H}_2\text{O} \]

### Step 4: Final Reaction to Produce Potassium Dichromate
In the final step, sodium dichromate (Na2Cr2O7) is reacted with potassium chloride (KCl) to produce potassium dichromate (K2Cr2O7) and sodium chloride (NaCl).

**Reaction:**
\[ \text{Na}_2\text{Cr}_2\text{O}_7 + 2\text{KCl} \rightarrow \text{K}_2\text{Cr}_2\text{O}_7 + 2\text{NaCl} \]

### Conclusion
Thus, the starting material used for the preparation of potassium dichromate is **FeCr2O4**, which is known as chromite.

### Final Answer
The correct option is **FeCr2O4 (chromite)**.

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