Some Important Compounds of Boron

Boron is a non-metal, it is the fifth element in the periodic table. It is represented by the B symbol and the atomic number of boron is 5 it belongs to the family of p-block elements in the periodic table. 

Boron is one of the most abundant elements. Its amount is very less in earth’s crust say nearly 0.0001% by mass. It occurs in different forms as borax, orthoboric acid or kernite. In India Boron can be found as borax in Rajasthan and Ladakh. 

Boron is an isotopic element so there are two isotopes of boron one with 10 as its atomic mass and the other one having 11 as its atomic mass.

Properties of Boron are:

1. It occurs in both forms crystalline and amorphous.
2. Its appearance is dark in crystalline form.
3. It appearance is brown in its amorphous form.
4. At STP( standard temperature and pressure) it has a solid phase.
5. It has high melting and boiling point.
6. It has a rhombohedral structure.
7. It is a lustrous metalloid.

Uses of Boron are:

• Boron is used in making fibreglass.
• Boron is used as a fuel igniter in rockets in its amorphous form.
• Boron in the form of boric acid is used to make Pyrex.
• Some isotopes of boron are good neutron absorbers so they are used in nuclear reactors for controlling nuclear reactions.
• Boron is also used in medical fields for the treatment of some kind of brain tumours.
• For plants, boron is helpful in keeping cell walls healthy.
• Boron is used in the agriculture industry for making liquid fertilisers

Some important Compounds of Boron

Borax

Borax is one of the most important compounds of Boron. Its formula is Na₂B₄O₇⋅10H₂O. Its name is Sodium tetraborate decahydrate. 

Borax is soluble in water. Borax yields sodium hydroxide and orthoboric acid when dissolved in water.

Na₂B₄O₇   +   7H₂O   →   2NaOH   +    4H₃BO₃ (Orthoboric acid) 

Borax turned into a transparent liquid when heated for a long time, this transparent liquid when cools down and solidifies results in the formation of a borax bead. The borax bead is used for the testing of different metaborates. Borax gives a blue flame when heated with cobalt oxide coated on the platinum wire.

Properties of Borax are:

• Borax has a high melting point of 743^ο Celsius and boiling point is 1575^ο C.
• It is a colourless compound.
• Its crystal structure is of square shape.
• It has a ph of 9.13.
• Its solution is alkaline in nature.
• It is a soft compound that is water-soluble.

Uses of Borax are:

• Borax is mainly used in stain cleaners.
• It has the capacity to kill small insects such as ants so it is used for that purpose also.
• One of the essential use of borax is softening of hard water.
• It is also used in making antiseptics.
• Borax is now an essential compound for the paint industry also.
• Herbicides and fungicides also use borax.

Orthoboric acid

Orthoboric acid is a chemical compound with the formula H₃BO₃. It is formed when borax is dissolved in water. It is a weak Lewis acid. 

Useful for many industries orthoboric acid is soapy to touch. It is soluble in water and alcohol. It was first prepared in 1702 by Wilhelm Homberg. It has a layered structure and is also flame retardant.

Properties of Orthoboric acid are:

• Orthoboric acid is a white crystalline solid.
• It is slippery to touch.
• It is highly soluble in hot water while mildly soluble in cold water.
• Metaboric acid is formed when orthoboric acid is heated up.
• It has a melting point of 170.9^ο celsius.
• The structure of Orthoboric acid has different layers of BO₃ units.
• It is not harmful if eaten by mistake.

Uses of Orthoboric acid are:

• It is used in making heat resistant glasses.
• It is used for the preservation of food items.
• It is used in making insecticides and pesticides.
• The cosmetic industry is also using orthoboric acid in making different cosmetic items.
• It is used in fireproofing of homes as orthoboric acid makes the wood fireproof.
• Also used in making pottery and enamels.

Diborane

Diborane has a formula B₂H₆ and it is a hydride of boron. It can be prepared by mixing boron trifluoride with LiAlH4 in diethyl ether. 

The chemical reaction can be written as:

4BF₃  +   3LiAlH₄   →   2B₂H₆   +   3LiF   +   3AlF₃

Reaction of sodium hydride and BF₃ at 450 Kelvin temperature also produces diborane and this technique is used in industries to produce diborane for commercial purposes.

Properties of Diborane are:

• It is a colourless compound of boron.
• The boiling point is 180 Kelvin.
• It is highly toxic in nature.
• Catches fire when exposed to air so it is highly dangerous.
• Has a planar structure with B-H and B-H-B bonds.
• Produces a large amount of energy when burnt in presence of oxygen.

Uses of Diborane are :

• Diborane is used in the vulcanisation of rubber.
• It is also used in rocket propellants.
• Also used as a catalyst in many polymer reactions.
• In electrical industries, it is used to give electrical properties to crystals that are pure in nature so some impurity is added as in doping.
• As diborane easily catches fire so it is used as a flame speed accelerator.
• It is also used as a reducing agent in many chemical reactions.

Sample Questions

Question 1: Is borax acidic or basic in nature?

Answer: 

Borax, when dissolved in water, produces a huge amount of hydroxide ions which are in the form of sodium hydroxide, it hides the acidity effect of orthoboric acid and thus borax is mainly basic in nature, also borax has a ph of 9.13 which clarifies that it is basic.

Question 2: Name some fruits which have boric acid?

Answer: 

Apples, Bananas, Almonds, Peanuts and many more fruits have some amount of boric acid in them. 

Question 3: What will happen if we excessively heat orthoboric acid?

Answer: 

Metaboric acid will be formed on heating orthoboric acid if heated more than boric oxide will be formed.  

H₃BO₃  (heat) ⇒ HBO₂ (Metaboric acid) (heat) ⇒ B₂O₃ (Boric Oxide)

Question 4: What happens when borane is hydrolysed?

Answer: 

Boranes when hydrolysed by water gives boric acid as a result. It can be understood by the following reaction:

B₂H₆(gas) + 6H₂O(liquid) → 2B(OH)₃(aq) + 6H₂ (gas) 

Question 5: Why is boric acid considered a weak acid?

Answer: 

It is considered a weak acid as it is not able to release H⁺ ions on its own because firstly it takes OH^– ions from water and then after completing its octet releases H⁺ ions.