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  • What reactions take place in borax bead test of copper in a reducing flame? a.<img alt="\mathrm{CuSO_4 + B_2O_3 \rightarrow Cu(BO_2)_2 + SO_3}" src="/latex-image/?%5Cmathrm%7BCuSO_4%20&am

What reactions take place in borax bead test of copper in a reducing flame?

a.\mathrm{CuSO_4 + B_2O_3 \rightarrow Cu(BO_2)_2 + SO_3}

b.\mathrm{2Cu(BO_2)_2 + 2NaBO_2 + C \rightarrow 2CuBO_2 + Na_2B_4O_7 + CO}

c.\mathrm{2Cu(BO_2)_2 + 4NaBO_2 + 2C \rightarrow 2Cu+ 2Na_2B_4O_7 + 2CO}

d. All of them

Option: 1

a, b


Option: 2

  b, c


Option: 3

a, c


Option: 4

d


Answers (1)

best_answer

Two reactions may take place in the reducing flame:

(i) The blue \mathrm{Cu (BO_2)_2} is reduced to colourless cuprous metaborate as follows:

\mathrm{2Cu(BO_2)_2 + 2NaBO_2 + C \rightarrow 2CuBO_2 (colourless\: \: bead) + Na_2B_4O_7 + CO }

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

\mathrm{2Cu(BO_2)_2 + 4NaBO_2 + 2C \rightarrow 2Cu (red \: opaque \: \: bead) + 2Na_2B_4O_7 + 2CO}

Hence option 2 is correct.

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