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STD 11 -p-Block elements - I — NEET STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceNEETSTD 11 -p-Block elements - I4 Marks
MCQ
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 observed 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 true
  • B
    Statement $I$ is true but Statement $II$ is false
  • ✓
    Both Statement $I$ and Statement $II$ are false
  • D
    Statement $I$ is false but Statement $I$ is true
✓

Answer

Correct option: C.
Both Statement $I$ and Statement $II$ are false
c
(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.

$CuSO _4+ B _2 O _3 \longrightarrow Cu \left( BO _2\right)_2+ SO _3$

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 :

$2 Cu ( BO _2 )_2+2 NaBO _2+ C \underset{\text { flame }}{\stackrel{\text { Luminous }}{\longrightarrow}} 2 CuBO _2+$ $ Na _2 B _4 O _7+ CO$

$(ii)$ Cupric metaborate may be reduced to metallic copper and bead appears red opaque.

$2 Cu \left( BO _2\right)_2+4 NaBO _2+2 C \underset{\text { fuminous }}{\stackrel{\text { flame }}{\longrightarrow}} 2 Cu +$ $2 Na _2 B _4 O _7+2 CO$

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