BORON:

Boron is metalloids of 13^th group and it does not occur in Free State. The major ores of boron are a small number of borate (boron oxide) minerals, including

PREPARATION OF BORON:

(1) From Borax: Boron may be obtained by treating borax with hot concentrated HCl, or H₂SO_4,  igniting the boric acid H₃BO₃ to give the oxide B₂O₃ and finally reduced with Na, K, Al, Mg.

Step-(1) conversion of borax into boron oxide:

Step-(2) conversion of Boron oxide into boron:

(2) From Colemanite:

Physical properties:

(1) It is a non-metal. Boron occurs in two different allotropic forms Amorphous and   Crystalline

(2) Amorphous boron has not been obtained in the pure state.

(3) Crystalline boron is a black powder, extremely hard with a metallic appearance but with very low electrical conductivity.

Chemical properties:

(1) Reaction with non oxy acids:

(2) Reaction with Oxy acids:

(3) Reaction with Oxy water:

(4) Reaction with Base:

(5) Reaction with Metals:

(6) Reaction with Non-metals

 (7) Reaction with Ammonia:

Structure of Borazine:

BORIC ACID (H3BO3) and its structural features:

Orthoboric acid, H₃BO_3, commonly known as boric acid, and Metaboric acid, HBO₃ , are two common oxy acids of  boron . Orthoboric acid naturally found in volcanic steam vents called Suffioni. 

STRUCTURE OF BORIC ACID:

(1) In dilute Solution Boric acid exist as monomeric form;

(2) When concentration of the solution of acids  is very high then boric acid exist as polymeric metaboric and many more ions.

(3) In Solid State It exist sp3 hybridised BO3-  2D Sheet .

 GENERAL PROPERTIES:

(1) H₃BO₃ is soluble in water and behaves as weak monobasic acid. It does not donate protons but rather it accepts OH^- .Therefore it acts as a Lewis acid [B(OH)₃] .It is not a proton donor because it accept lone pair or hydroxyl ion from water.

(2) Since B(OH)₃ only partially reacts with water to form H₃O⁺ and [B(OH)₄]^- it behaves as a weak acid. Thus it cannot be titrated satisfactorily with NaOH as a sharp end point is not obtained.  

(3)  B(OH)₃ (Boric acid ) does not  titrated even strong alkali like NaOH but If certain polyhydroxy compounds such as glycerol, mannitol or sugar are added to the titration mixture then B(OH)₃ behaves as a strong monobasic acid and hence can be titrated with NaOH and end point is diluted using phenolphthalein as indicator.

(4) The added compound must be a cis-diol to enhance the acidic proprieties. In this way the cis-diol forms very stable complexes with [B(OH)₄]¯ formed in forward direction above, thus effectively removing it from solution. Hence reaction proceeds in forward direction (Le-Chatelier principle.)

PHYSICAL PROPERTIES:

CHEMICAL PROPERTIES:

USES:

Related Questions:

What is structure of solid Ortho Boric acid ?

Why Boric acid become strong acid in the presence of cis 1,2-diol or 1,3-diol ?

What is the structure of trimetaboric acid and trimetaborate ion?  

What is basicity of "Boric acid" ?

Why Boric acid exist in solid state ?

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BORAX BEAD TEST:

When Borax is heated on loop of platinum wire then loop of platinum wire swells up due to loss of water of crystal of borax, if it is further heated then a transparent glass of Sodium metaborates (NaBO₂) and boric anhydride (B₂O₃) is obtained which  is called borax Bead. 

When a solution of given salt is heated on bead , then volatile part of salt displaced by B₂O₃  and corresponding metaborates salt is formed which gives Characteristic colour on oxidizing and reducing flame and colour of the bead is noted in hot and cold for each type of flame .

Chemical reactions:

Illustrative example of copper:

In oxidising flame;

In Hot flame: green colour transparent glassy bead appear

In Cold: Blue colour transparent glassy bead appear

In reducing flame;

IMPORTANT NOTE:
In this bead test colour of bead of metaborates of given basic radicals are formed provided  the metal cation must contain at least one unpaired electron , Orthoborates are also formed  but they are not responsible for bead colour.

SUMMARY OF BORAX BEAD TEST:

ILLUSTRATIVE EXAMPLE (1): Which of the following do not respond borax bead test?

     (1) Nickel Salts               (2) Copper Salts             (3) Cobalt Salts      (d) Aluminium Salts

ILLUSTRATIVE EXAMPLE (2): the “Borax Bead “Contains:

       (1)  NaBO₃                    (2) NaBO₂                       (3) B₂O₃                 (d) Na₂ B₄O₇.10H₂O  

ILLUSTRATIVE EXAMPLE (3): This Cation gives a colourless bead in Borax Bead Test:

       (1) Mg²⁺                        (2) Ca²⁺                            (3) Cu⁺¹                  (4) Cu⁺² 

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