Question

Explain the following reactions (a) Silicon is heated with methyl chloride at high temperature in the presence of copper; (b) Silicon dioxide is treated with hydrogen fluoride; (c) \(\mathrm{CO}\) is heated with \(\mathrm{ZnO}\); (d) Hydrated alumina is treated with aqueous NaOH solution.

Short answer

(a) Formation of chlorosilanes; (b) SiO₂ + HF → SiF₄ + H₂O; (c) ZnO + CO → Zn + CO₂; (d) Al(OH)₃ + NaOH → NaAlO₂ + H₂O.

Step-by-step solution

Understand the Reaction (a)

Silicon is heated with methyl chloride (CH₃Cl) at high temperatures in the presence of copper. This is a typical preparation method for organosilicon compounds. The copper acts as a catalyst. In this reaction, silicon reacts with methyl chloride to form a mixture of methyl-substituted chlorosilanes, primarily dimethyldichlorosilane (CH₃)₂SiCl₂ after purification.

Equation for Reaction (a)

The chemical equation for this reaction can be written as:\[2 ext{CH}_3 ext{Cl} + ext{Si} \xrightarrow{ ext{Cu, heat}} (CH_3)_2 ext{SiCl}_2\]This is the basis of the industrial synthesis of silicones.

Understand the Reaction (b)

Silicon dioxide (SiO₂) is treated with hydrogen fluoride (HF). Silicon dioxide reacts with HF to form silicon tetrafluoride gas (SiF₄) and water. This reaction shows the acid-base reaction where SiO₂ acts as an acid while HF acts as a base.

Equation for Reaction (b)

The equation for this reaction is:\[SiO_2 + 4HF \rightarrow SiF_4 + 2H_2O\]This reaction is used in glass etching and microelectronics.

Understand the Reaction (c)

Carbon monoxide (CO) is heated with zinc oxide (ZnO). This reaction is a reduction reaction, where CO reduces ZnO to zinc (Zn) metal while itself getting oxidized to carbon dioxide (CO₂). This is a common method for extracting zinc from its oxide.

Equation for Reaction (c)

The balanced chemical equation is:\[ZnO + CO \rightarrow Zn + CO_2\]This reduction process is significant in metallurgy.

Understand the Reaction (d)

Hydrated alumina (Al(OH)₃) is treated with aqueous NaOH solution. This results in the formation of sodium aluminate (NaAlO₂) and water. The alumina dissolves in NaOH, reflecting its amphoteric nature.

Equation for Reaction (d)

The balanced equation for the reaction is:\[Al(OH)_3 + NaOH \rightarrow NaAlO_2 + 2H_2O\]This reaction illustrates the amphoteric nature of aluminum hydroxide.

Key concepts

Organosilicon Compounds

Organosilicon compounds are intriguing substances that combine organic groups with silicon atoms. These compounds have widespread use, particularly in the manufacture of silicones, which are known for their flexibility, durability, and resistance to extreme temperatures.
When silicon (\( \text{Si} \)) is heated with methyl chloride (\( \text{CH}_3\text{Cl} \)) in the presence of copper, a catalytic reaction occurs. Copper acts as a catalyst to lower the energy barrier, allowing the reaction to proceed efficiently.
This process results in the formation of dimethyldichlorosilane (\( (\text{CH}_3)_2\text{SiCl}_2 \)), a key component in producing silicone. This reaction is crucial for creating silicones used in everything from sealants to medical devices.
The reaction is represented by:\[ 2 \text{CH}_3\text{Cl} + \text{Si} \rightarrow (\text{CH}_3)_2\text{SiCl}_2 \]}},{

Acid-Base Reaction

An acid-base reaction can sometimes seem baffling, but it's essentially about the transfer of protons. In the exercise, silicon dioxide (\( \text{SiO}_2 \)) reacts with hydrogen fluoride (\( \text{HF} \)). Here, \( \text{SiO}_2 \) acts as an acid because it can donate protons. On the other hand, \( \text{HF} \) serves as a base, accepting these protons to form silicon tetrafluoride (\( \text{SiF}_4 \)) and water.
This reaction is vital in industries like glass etching and microelectronics, where precise material removal is required. In chemical terms, this is called an acidic oxide reacting with a base, forming a salt and water.
The chemical equation for this reaction is:\[ \text{SiO}_2 + 4\text{HF} \rightarrow \text{SiF}_4 + 2\text{H}_2\text{O} \]}},{

Reduction Reaction

Reduction reactions involve the gain of electrons by a molecule, atom, or ion. In the original exercise, carbon monoxide (\( \text{CO} \)) functions as a reducing agent when it is heated with zinc oxide (\( \text{ZnO} \)).
Here, \( \text{ZnO} \) is reduced to metallic zinc (\( \text{Zn} \)), while \( \text{CO} \) is oxidized to carbon dioxide (\( \text{CO}_2 \)). This reaction is critical in the metallurgy field for extracting zinc from its oxide forms.
It is a classic example of a redox reaction, where one species is reduced and the other is oxidized.
The balanced chemical equation for this process is:\[ \text{ZnO} + \text{CO} \rightarrow \text{Zn} + \text{CO}_2 \]}},{

Amphoteric Nature

Amphoteric substances have the unique ability to behave both as an acid and a base. A classic example is hydrated alumina (\( \text{Al(OH)}_3 \)), which was highlighted in the exercise.
When \( \text{Al(OH)}_3 \) is treated with sodium hydroxide (\( \text{NaOH} \)), it dissolves to form sodium aluminate (\( \text{NaAlO}_2 \)), showcasing its amphoteric behavior. In this reaction, \( \text{Al(OH)}_3 \) acts as an acid, reacting with the base \( \text{NaOH} \).
This reaction is useful in industrial processes, such as the Bayer process for refining bauxite to produce alumina.
The balanced equation is:\[ \text{Al(OH)}_3 + \text{NaOH} \rightarrow \text{NaAlO}_2 + 2\text{H}_2\text{O} \]