Silicon is the second most abundant element `(~27.2%)` in the earth's after oxygen `(45.5 %)` Carbon. Silicon, germanium, tin and lead constitute the group `14` of the periodic table. Chemistry of silicon is distinctly different from that of carbon.
For example, under standard conditions `CO_(2)` is a gas whereas `SiO_(2)` is a covalent solid.
Draw the structure of the anion present in pyroxene `(MgCaSi_(2)O_(6))`.
Silicones are important synthetic polymers which find extensive applications due to their chemical inertness and water repelling nature. Thet are produced via the following reactions.
`2 C_(6)H_(5)Cl +Si underset("370 K")overset("Cu")to A`
`A underset(-HCl)overset(H_(2)O)to B`

Answer

To solve the question regarding the structure of the anion present in pyroxene (MgCaSi₂O₆) and the reactions leading to the formation of silicones, we will break it down into two parts.

### Part 1: Structure of the Anion in Pyroxene

1. **Identify the Composition of Pyroxene**:
- Pyroxene has the formula MgCaSi₂O₆. This indicates that it contains magnesium (Mg²⁺), calcium (Ca²⁺), silicon (Si), and oxygen (O).

2. **Determine the Charge of the Anion**:
- The magnesium and calcium ions each have a charge of +2. Therefore, the total positive charge from the cations is +4 (2 from Mg and 2 from Ca).
- To balance this, the overall charge of the anion must be -4.

3. **Identify the Anion Structure**:
- The anion can be represented as (Si₂O₆)⁴⁻. This indicates that there are two silicon atoms and six oxygen atoms in the anion.

4. **Draw the Structure**:
- Each silicon atom (Si) has a valency of 4 and can form bonds with oxygen atoms.
- Arrange the six oxygen atoms around the two silicon atoms.
- Two of the oxygen atoms will be bridging between the two silicon atoms, while the remaining four will be terminal oxygen atoms, each carrying a negative charge.

5. **Final Structure**:
- The structure can be represented as:
```
O O
\ /
Si - O - Si
/ \
O O
```
- The bridging oxygen atoms (O) connect the two silicon atoms, while the terminal oxygen atoms are negatively charged.

### Part 2: Reactions Leading to Silicones

1. **Identify the Reactions**:
- The reactions given are:
- `2 C₆H₅Cl + Si (370 K, Cu) → A`
- `A + H₂O (-HCl) → B`

2. **Reaction to Form A**:
- When chlorobenzene (C₆H₅Cl) reacts with silicon (Si) in the presence of copper at elevated temperature (370 K), it forms a compound known as diphenylchlorosilane (A).
- This compound has the structure:
```
C₆H₅
|
Si - Cl
|
C₆H₅
```

3. **Hydrolysis of A to Form B**:
- When diphenylchlorosilane (A) undergoes hydrolysis, it reacts with water (H₂O) and loses HCl.
- The hydrolysis replaces the chlorine atoms with hydroxyl groups (OH), resulting in diphenylsiloxane (B):
```
C₆H₅
|
Si - OH
|
C₆H₅
```

4. **Condensation to Form Silicones**:
- If further condensation occurs, the product can form linear silicones, where multiple siloxane (Si-O) linkages are formed.

### Summary of Products
- **Product A**: Diphenylchlorosilane (C₆H₅)₂SiCl
- **Product B**: Diphenylsiloxane (C₆H₅)₂Si(OH)