[Chemistry Class Notes] on Silicon Dioxide Pdf for Exam

What is Silicon Dioxide? 

Silicon Dioxide is a natural compound of oxygen and silicon, found mostly in the sand. It is also known as Silica, composed of silicon and oxygen, having chemical formula [SiO_{2}], or silicon dioxide. There are various forms of Silica, and all silica forms are identical in chemical composition but contain different atom arrangements. 

Silica has three primary crystalline varieties, quartz, tridymite, and cristobalite. Silica dust from fine particulate quartz rock causes a long-term progressive lung injury, silicosis. ([NCIO_{4}]). The [SiO_{2}] chemical name is Silicon Dioxide.

Silica compounds are further divided into amorphous Silica (a-silica or non-crystalline Silica) and crystalline (or c-silica).

c-Silica compounds have structures with repeating patterns of both silicon and oxygen.

a-Silica chemical structures are more randomly linked to that of c-silica. 

All silica forms are odourless solids composed of silicon and oxygen atoms obtained as transparent to grey in its crystalline or amorphous powdered form. Silica particles get suspended in air and form non-explosive dust. Silica can be combined with oxides and other metallic elements for the formation of silicates.

[SiO_{2}] Structure 

Silicon dioxide is otherwise called silicon (IV) oxide.

There exist three different silicon dioxide crystal forms. The easiest one to draw and remember depends on the diamond structure.

The crystalline silicon has a similar structure as diamond. To turn it into silicon dioxide, all we are supposed to do is modify the silicon structure by adding some oxygen atoms.

The simple [SiO_{2}] structure is represented in the following way.

If we notice properly, each silicon atom is bridged to its neighbour by an oxygen atom. Remember that this is just a tiny part of a giant [SiO_{2}] structure that extends on all three dimensions.

Silicon Dioxide Properties

The basic [SiO_{2}] properties of both physical and chemical are given below.

Physical Properties of [SiO_{2}]

Silicon dioxide is transparent to grey, crystalline, odourless, or an amorphous solid. They have melting and boiling points as 1713º C and 2950º C, respectively. The density is about 2.648 g/cm3. It is insoluble in both acid and water and soluble in hydrofluoric acid. Its molecular weight is about 60.08 g/mol.

Chemical Properties of [SiO_{2}]

Silicon dioxide is not a very reactive compound because the polarity of the molecule is zero. The ‘Si’ forms two double bonds with the oxygen. Therefore, it’s a very stable molecule. Moreover, it has high dielectric strength, so that it is used as an insulator and semiconductor.

Production of Silicon Dioxide

The acidification sodium silicate solutions obtain precipitated Silica or amorphous Silica. Its gel is washed and dehydrated to make colourless microporous Silica. The reaction involving a trisilicate along with sulfuric acid is provided below.

[Na_{2}Si_{3}O_{7} + H_{2}SO_{4} rightarrow 3SiO_{2} + Na_{2}SO_{4} + H_{2}O]

Silicon Dioxide Reactions

Silica is converted into silicon by reducing carbon.

When fluorine reacts with silicon dioxide, it produces [O_{2}] and [SiF_{4}].

Silicon dioxide also reacts with hydrofluoric acid to form hexafluorosilicic acid ([H_{2}SiF_{6}]).

[SiO_{2} + 6HF rightarrow H_{2}SiF_{6} + 2H_{2}O]

Preparation of Silicon Dioxide

Most of the silicon dioxide is extracted even from quartz mining, it can also be prepared using acid neutralisation of an aqueous alkali metal – silicate solution. This kind of method is known as a wet process and forms amorphous [SiO_{2}] particles.

[Na_{2}Si_{3}O_{7} + H_{2}SO_{4} rightarrow 3SiO_{2} + Na_{2}SO_{4} + H_{2}O]

The other methods form pyrogenic Silica, having silanes combustion like silicon tetrachloride, in an oxygen-hydrogen burner. These are the fine particle product aggregates of 100 – 400 nm in diameter.

[SiCl_{4} + 2H_{2} + O_{2} rightarrow SiO_{2} + 4HCl]

Applications of Silicon Dioxide

Silica exists as fluffy, and white powders produced through a wet process, yielding a thermal route, Silica, or silica gel, yielding a pyrogenic (fumed) silica.

In powdered foods, the Silica clings to the food particles and prevents them from clumping. Doing this allows powdery products to remain free-flowing, and to separate other products easily.

Also, Silicon dioxide functions as a defoaming agent, conditioning agent, carrier, chill proofing agent in malt beverages like beer and filter aid.

Besides, it is used in material manufacture like paper and adhesives for food-packaging materials.

As per the U.S. FDA regulation’s direct additive, the SAS levels cannot exceed 2% by the food weight, and as an indirect additive, it can be used only in the required amount to produce the intended functional effect.

Silicon Dioxide Uses

There is various Silicon dioxide used in electronic, chemical, and pharmaceutical industries. In the chemical industry, it is used in the production of adhesives and sealants, adsorbents, ceramic, porcelain, corrosion inhibitors, anti-adhesives, dyes, and paint additives. In addition, silicon dioxide production occurs in agricultural chemicals. Coming to pharmaceutical industries, it helps as an additive of food and medicines to absorb water. For telecommunication, [SiO_{2}] is the main component of optical fibres. Silicon dioxide is extensively used as a precursor to obtaining glass and silicon by the reaction given below.

[SiO_{2} + 2C rightarrow Si + 2CO]

Furthermore, Silicon dioxide is also used in the construction industry to produce concrete. Used in hydraulic fracturing in its crystalline form, and in glass production, as a Sedative, production to produce elemental silicon, as an anti-caking agent in powdered foods such as spices, as a fining agent in beer, juice, and wine, in pharmaceutical tablets, and in toothpaste to remove the tooth plaque.

Health Hazards

Orally Silica is non-toxic when ingested. According to a study report conducted in 2008, the higher the rates of Silica in water, the lower the likelihood of dementia. As a result, the dosage was raised to 10 mg/day of silica in drinking water as the incidence of dementia reduced. When silica dust of finely divided crystalline is inhaled, it may lead to lung cancer, bronchitis, or silicosis, because of the lodging of dust in the lungs. Also, when fine particles of Silica are inhaled in excessive quantities, it increases the risk of lupus and rheumatoid arthritis.