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.
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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