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What is borax bead test?
Borax -bead test : Boric anhydride reacts with certain metal salts such as Ni2+,Co2+,Cr3+,Cu2+.Mn2+etc salt to form coloured metaborates.The colour of the metaborates can be used to identify the metallic ion in the salt .
    A small quantity of borax is taken on a small loop of platinum wire .On heating in a flame a transparent bead is formed .The hot transparent bead is touched with the salt when few particles stick to it .The bead (with the sticking salt ) is then heated in an oxidising flame (outer zone ) and then in a reducing flame (luminous zone ) .From the colour of the bead when hot and when cold, the basic radical present in the salt can be identified .
    Certain metaborates are reduced to free metal in a reducing flame .For metals with variable valence ,the metaborates changes to lower valence state .For example ,with copper sulphate ,the borax bead test gives

Nickel salts give brown coloured bead ,cobalt gives blue coloured bead ,while chromium salt gives green bead .


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