Subject: Chemistry
Boron is a Group 13 element which is borderline between metals and non-metals. It is better to term it as semiconductor than a conductor. Chemically, it is closer to silicon than to aluminium, gallium, indium, and thallium.
Crystalline boron is inert chemically. When finely divided, it is attacked slowly by hot concentrated nitric acid.
Extraction
Boron is extracted from borax {Na2B4O7.10H2O}. When borax is boiled with concentrated HCl & followed by hydrolysis then, boric acid is obtained. On heating boric acid, it produces boric anhydride on reduction with Hg produce boron.
$$Na_2B_4O_7+2HCl+5H_2O\longrightarrow 2NaCl+4H_3BO_3$$
$$2H_3BO_3\longrightarrow B_2O_3+3H_2O$$
$$B_2O_3+3Mg\longrightarrow 2B+3MgO$$
Properties
Isotope | Mass/ | Natural abundance (atom %) |
10B | 10.012 937 0(4) | 19.9 (7) |
11B | 11.009 305 5(5) | 80.1 (7) |
Uses
Dehydrated sodium tetraborate is borax. The natural deposit of borax is called tincal. Tincal is 55% borax.
Preparation
It is prepared by heating colemanite with sodium carbonate and water.
$$2Ca_2B_6O_{11}+3Na_2CO_3+H_2O\longrightarrow 2Na_2B_4O_7+3CaCO_3+Ca(OH)_2$$
Finally, crystallization is done and crystals of borax can be found.
Properties
On heating, it loses water of crystallization forming anhydrous and then sodium metaborate and finally changes to boric oxide.
$$Na_2B_4O_710H_2O\longrightarrow Na_2B_4O_7\longrightarrow 2NaBO_2+B_2O_3$$
Uses
It is also known as orthoboric acid. It can be prepared as:
Properties
Uses
Structure
Uses
It was discovered on 1824 by Jons Jacob Berzelius. The name is derived from the Latin 'silex' or 'silicis'. The earth is constructed of silicon, and silicon is very useful in daily life as we use it in the form of glass and pottery. The pure silicon is a solid and a blue-grey metal. Silica (SiO2) in the form of sharp flints were used by ancestors as the weapon.
Group | 14 | Melting point | 1414°C, 2577°F, 1687 K |
Period | 3 | Boiling point | 3265°C, 5909°F, 3538 K |
Block | p | Density (g cm−3) | 2.3296 |
Atomic number | 14 |
The isotopic form of silicon are
Isotope | Atomic mass | Natural abundance (%) |
28Si | 27.977 | 92.223 |
29Si | 28.976 | 4.685 |
30Si | 29.974 | 3.092 |
Uses
Preparation of Silicon Dioxide
Silica is prepared by the hydrolysis of silicon tetrachloride, heating the hydrated oxide silicon dioxide is formed.
$$SiCl_4+4H_2O↔SiO_2⋅2H_2O+4HCl$$
Properties of Silicon Dioxide
Silica is a transparent solid and has high melting point.
Silica is inert to most chemical reagents but reacts with hydrogen fluoride and this help in the formation of silicon tetrafluoride, which is a colourless gas at room temperature and water.
Silica is an acidic oxide and is capable to reacts with alkalis to form salt and water.
$$SiO_2+2NaOH↔Na_2SiO_3+H_2O$$
Properties of Silicon Dioxide
Silicon dioxide is a crystalline compound. It is used to transmits visible and ultraviolet light. Many crystalline forms exist, the most common is Quartz.
Uses of Silicon Dioxide
Pure silicon dioxide is an important material in the electronics industry.
When silica reacts with solid sodium carbonate and is melted, sodium silicate is formed.
$$SiO_2+Na_2CO_3↔Na_2SiO_3+CO_2$$
Reference
pulse, Tracy. Introduction to chemistry. u.s.a: flex book, 2010.
Pathak, Sita Karki. The Text Book of Chemistry. Kathmandu: Vidhyarthi Pustak Bhandar, 2012.
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