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Saturday, January 26, 2019


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;
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.
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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