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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