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P Block Elements question

2023 · 31 Jan · Shift 2 · Q11
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P Block Elements question

2023 · 31 Jan · Shift 2 · Q11

JEE MainChemistryP Block ElementsMCQ+4 / −1
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 light of the above statements, choose the most appropriate answer from the options given below :
  1. A
    Both Statement I and Statement II are false
  2. B
    Both Statement I and Statement II are true
  3. C
    Statement I is false but Statement II is true
  4. D
    Statement I is true but Statement II is false
View written solutionFree

Correct answer: A

  1. Borax bead test with copper salts

    Borax on heating forms a glassy bead containing boric anhydride and sodium metaborate: Na2B4O7→heat2NaBO2+B2O3\mathrm{Na_2B_4O_7 \xrightarrow{heat} 2NaBO_2 + B_2O_3}Na2​B4​O7​heat​2NaBO2​+B2​O3​

    Metallic oxides dissolve in this bead to give characteristic colours.

  2. Effect of flame type

    • In an oxidising (non-luminous) flame, copper gives a blue/blue-green bead due to formation of cupric metaborate: CuO+B2O3→Cu(BO2)2\mathrm{CuO + B_2O_3 \rightarrow Cu(BO_2)_2}CuO+B2​O3​→Cu(BO2​)2​
    • In a reducing (luminous) flame, Cu2+\mathrm{Cu^{2+}}Cu2+ is reduced to Cu+\mathrm{Cu^+}Cu+, and the bead becomes red/opaque because of formation of cuprous oxide or metallic copper, not green.

  3. Check Statement I

    Statement I says: Upon heating a borax bead dipped in cupric sulphate in a luminous flame, the colour of the bead becomes green.

    This is false, because in a luminous (reducing) flame, copper does not give a green bead.

  4. Check Statement II

    Statement II says: The green colour observed is due to the formation of copper(I) metaborate.

    This is also false:

    • The green/blue-green colour is associated with copper(II) borate species, not copper(I) metaborate.
    • In reducing flame, copper(I) species do not produce the stated green borax bead result.

  5. Conclusion

    • Statement I: False
    • Statement II: False

    Therefore, the correct option is: A\boxed{\text{A}}A​

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