Question

State with equation what happens when borax is heated on a platinum wire loop and to the results tranparent mass, a minute of `CuO` is added and the mixture is again heated first in oxidising flame and then in the reducing flame of a Bunsen burner ?

Answer 1

When borax is heated on a platinum wire loop. A transparent glassy bead is heated with `CuO` in the oxidising flame, it imparts blue colour to the bead due to the formation of cupric metaborate
`CuO + B_(2)O_(3) overset("Oxidising flame")rarr underset("Cupric metaborate (blue)")(Cu (BO_(2))_(2))`
However, when cupric metaborate is heated in the reducing flame of the Bunsen burner, the blue cupric metaborate is reduced by carbon present in the flame first to colourless currous metaborate and the then to metal and produces red scales.
`{:(underset(("blue"))underset("Cupric metaborate")(2Cu(BO_(2))_(2))+Crarrunderset(("colourless"))underset("Cuprous metaborate")(2CuBO_(2))+B_(2)O_(3)+CO),(2CuBO_(2) + C rarr underset(("red"))underset("Copper metal")(Cu)+B_(2)O_(3)+CO):}`