Question

Borate form green edged flame when burnt with conc. $H_2{SO}_4$ + ethanol. Green edged flame has formula:

• A. $H_2{SO}_4$
• B. $({C_2{H}_5)}_2{BO}_2$
• C. $({C_2{H}_5)}_3{BO}_3$
• D. none of the above

Answer 1

Answer: (C)

$({C_2{H}_5)}_3{BO}_3$

When borax is heated with ethanol and conc. $H_{2}S{O}_4$, vapours of triethyl borate are produced that burn with a green edged flame.
This green edged flame test for testing $B{O}_3^{3-}$ radical is written as follows:
$N{a}_2{B}_4{O}_7+H_{2}S{O}_4+5H_{2}O\to N{a}_{2}S{O}_4+4H_{3}B{O}_3$
$H_{3}B{O}_3+C_2{H}_{5}OH\to (C_2{H}_5{)}_{3}B{O}_3+3H_{2}O$
Triethyl Borate