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

Hint:

In the Borax Bead Test, the formation of cupric metaborate gives the bead its blue-green colour in the reducing flame, not copper(I) metaborate.

Answer 1

The Correct Option is A

(Borax Bead Test)
On treatment with metal salt, boric anhydride forms metaborate of the metal which gives different colours in oxidising and reducing flames. For example, in the case of copper sulphate, following reactions occur.

\( \text{CuSO}_4 + \text{B}_2\text{O}_3 \xrightarrow{\text{Non-luminous flame}} \text{Cupric metaborate blue-green} \)

Two reactions may take place in reducing flame (Luminous flame):

(i) The blue-green \( \text{Cu(B}_2\text{O}_3)_2 \) is reduced to colourless cuprous metaborate:

\( 2 \, \text{Cu(B}_2\text{O}_3)_2 + 4 \, \text{NaBO}_2 \xrightarrow{\text{Luminous flame}} 2 \, \text{Cu} + 2 \, \text{Na}_2\text{B}_4\text{O}_7 + \text{CO}_2 \)

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

\( 2 \, \text{Cu(B}_2\text{O}_3)_2 + 4 \, \text{NaBO}_2 \xrightarrow{\text{Luminous flame}} 2 \, \text{Cu} + 2 \, \text{Na}_2\text{B}_4\text{O}_7 + \text{CO}_2 \)

So, the correct answer is (A): Both Statement I and Statement II are false.