Question

The coloured bead produced When borax is heated with cubic content unit an oxidizing flame is :
A). greenish
B). green when hot & blue when cold
C). yellow
D). red

Answer 1

If an excessive amount of substance is employed, the bead will become dark and opaque. The bead and adhering substance is then heated within the lower, reducing, a part of the flame, allowed to cool down, and therefore the colour observed.

Complete step by step answer:
The coloured metaborate $Cu\left( {BO_2} \right)_2$ formed when borax is heated with Cu is green when hot and blue when cold. attiny low loop is created within the end of a platinum or nichrome wire and heated in an exceedingly gas jet flame until hotdog.
The bead is allowed to chill so wetted and dipped into the sample to be tested specified only a small amount of the substance adheres to the bead. If an excessive amount of substance is employed, the bead will become dark and opaque.
The bead and adhering substance is then heated within the lower, reducing, a part of the flame, allowed to chill, and also the colour observed. it's then heated within the upper, oxidizing, a part of the flame, allowed to cool down, and also the colour observed again.
Characteristic coloured beads are produced with salts of copper, iron, chromium, manganese, cobalt and nickel. After the test, the bead is removed by heating it to fusion point, and plunging it into a vessel of water.

So, the correct answer is Option B.

Note: The bead test could be a traditional part of qualitative inorganic analysis to check for the presence of certain metals. The oldest one is the borax bead test or blister test. it had been introduced by Berzelius in 1812.