Question

Given below are two statements :
Statement I : Upon heating a borax bead dipped in cupric sulphate in a luminous flame, the colour of the bead becomes green
Statement II : The green colour observerd is due to the formation of copper(I) metaborate
In the light of the above statements, choose the most appropriate answer from the options given below :

• A. Both Statement I and Statement II are false
• B. Both Statement I and Statement II are rue
• C. Statement I is false but Statement II is true
• D. Statement I is true but Statement II is false

Answer 1

Answer: (A)

(Borax Bead Test)
On treatment with metal salt, boric anhydride forms metaborate of the metal which gives different colours in oxidising and reducing flame. For example, in the case of copper sulphate, following reactions occur.
$CuSO _4+ B _2 O _3 \xrightarrow[(\text { Oxidising ) }] {\text { Non -luminous flame }} \underset{\text{Cupric metaborate blue-green}}{Cu \left( BO _2\right)_2+ SO _3}$
Two reactions may take place in reducing flame (Luminous flame)
(i) The blue-green $Cu \left( BO _2\right)_2$ is reduced to colourless cuprous metaborate as :
$2 Cu \left( BO _2\right)_2+2 NaBO _2+ C \xrightarrow[\text { flame }]{\text { Luminous }} $
$2 CuBO _2+ Na _2 B _4 O _7+ CO$
(ii) Cupric metaborate may be reduced to metallic copper and bead appears red opaque.
$ 2 Cu \left( BO _2\right)_2+4 NaBO _2+2 C \xrightarrow[\text { flame}] {\text { Luminous}}$
$ 2 Cu +2 Na _2 B _4 O _7+2 CO$