Carbon monoxide (CO)

Preparation

• It is prepared from incomplete combustion of carbon as given in reaction below :

C + ½ O₂  –>CO

_{Carbon oxygen   carbon monoxide}

• Heating Methanoic acid in presence of sulphuric acid at temperature 473-1273 k.

HCOOH + H₂SO₄— >CO + H₂O

_{Methanoic acid     sulphuric acid      carbon monoxide  and water}

• Commercial preparation: Heating Coke with water at high temperature.

C + H₂O  –> CO + H₂

_{Carbon  water       syn gas}

If we mix carbon in air :

C + O₂+ 4N₂  –> CO + N₂

  _{carbon   oxygen   nitrogen    carbon monoxide and nitrogen gas}

Properties

• It is colourless and odourless.
• It is insoluble in water.
• It is highly toxic in nature as it combines with Haemoglobin,to form defective complex .As a result, the oxygen carrying capacity of RBC gets reduced.
• It burns in air to form carbon dioxide.

Uses

• It acts as reducing agent in extraction of metals.
• It reacts with certain metals to form Metal carbonyls.
• It forms synthesis gas that has industrial advantage.
• It forms producer gas that has industrial advantage.

Carbon dioxide (CO₂)

Preparation

• From complete combustion of Carbon and Carbon containing fuels in excess of air:

                     C + O₂ — >CO₂

                           _{carbon oxygen carbondioxide}

                  CH₄+ O₂ –.>CO₂ + H₂O

                        _{Methane   carbon dioxide and water}

Properties

• It is colourless and odourless.
• It is soluble in water.
• It is non supporter of combustion.
• It combines with water to for Carbonic acid (weak dibasic acid).

     Uses

• It forms carbonic acid which undergo dissociation as :

This H₂CO₃ and HCO₃^– helps in maintaining pH of blood between 7.26  to     7.42.

• Carbon dioxide is used by plants for photosynthesis: If the percentage of this gas increases in atmosphere, it has adverse affect like green house effect, which further results in ecological imbalance .
• Dry ice (solid form of carbon dioxide) is used as refrigerant for ice creams and frozen food.
• Gaseous carbon dioxide is used in carbonated soft drinks.
• Carbon dioxide is used in fire extinguisher as it is non supporter of combustion.

Silicon dioxide (SiO₂)

About 95% of earth crust is made up of silica and silicates .Silicon dioxide is commonly called as silica and it occurs in different forms :

Crystalline form of silica

• Quartz
• Cristobalite
• Tridymite

These forms are inter-convertible at suitable temperature.

Structure of Silicon dioxide

• This silicon tetra fluoride can easily dissolves in HF to form H₂SiF₆ (hydro-Fluoro-silicic acid ).
• Due to formation of this compound, the SiO₂ present in glass gets dissolved. That is the reason the hydrogen fluoride can’t be stored in glass bottles, instead it is stored in containers made of Cu, Ni+ traces of Fe alloy .
• Quartz is used as piezoelectric material.

Uses

• Silicon dioxide is used as catalyst in petroleum industry.
• When (NH₄)₂CoCl₄ is added to silica gel , it act as a humidity detector .Since ,it is blue when dry but turns pink when hydrated .

Silicones

• They are synthetic organo-silicon compounds containing repeated R₂SiO units held by Si-O-Si linkages.
• These compounds have the general formula (R₂SiO)_n where R is methyl or aryl group .

Preparation  

• The methyl chloride reacts with Silicon in presence of Copper at temperature 573k.
• As a result, we get different types of methyl substituted cholrosilane of formulas :MeSiCl₃, MeSiCl₂, Me₃SiCl and also Me₄

CH₃Cl + Si –> (CH₃)₂SiCl₂

_{methyl chloride          dichloromethylsilane}

                      (CH₃)₂SiCl₂   + H₂O –> (CH₃)₂Si(OH)₂

                                       _{Dichloromethylsilane}

• If we carry out hydrolysis of dichlorodi-methylsilane followed by polymerization we get , straight chain polymers

 Properties

• Silicones with :
• Short chains – oily liquids
• Medium chain- viscous oils, jellies and greases
• Long chains – rubbery elastomers and resins .
• They are chemically inert, resistant to oxidation and thermal decomposition.
• Silicones are surrounded with non polar alkyl group that are water repelling in nature.
• They are heat resistant and possess high dielectric constant.

Uses

• They are used in making water proof papers, wool ,textile, wood  etc by coating them with thin film of silicones.
• They are used as electric insulators.
• They are used as lubricants at high as well as at low temperature , as there is very little change in their viscosity with temperature.
• They are used in surgical implants.

Zeolites

• They are widely used as catalyst in petrochemical industries for cracking of hydrocarbons.
• In them basically the Silicon atoms in three dimensional structures is replaced by Aluminum ions.
• As a result, the overall structure carries the negative charge .
• To balance this negative charge some cations like sodium ion etc are added in the structure.

   For example:

1. ZSM-5 a type of zeolite converts alcohols directly to gasoline.
2. Hydrated zeolite is used as permutit in ion exchange method for softening of hard water.