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- JEE Main
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- Chemistry
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- Practical Chemistry
JEE Main · Chemistry · Practical Chemistry
Which of the following statements regarding the borax bead test of...
Which of the following statements regarding the borax bead test of transition metal salts is INCORRECT?
Options
- ACobalt salts yield a deep blue bead in both oxidizing and reducing flames.
- BChromium salts produce a green bead in both oxidizing and reducing flames.
- CCopper salts form a blue bead when heated in a reducing flame.
- DManganese salts give an amethyst coloured bead in an oxidizing flame and a colourless bead in a reducing flame.
Correct answer
C. Copper salts form a blue bead when heated in a reducing flame.
Step-by-step solution
In the borax bead test, different transition metals form characteristic coloured metaborates depending on the nature of the flame.
Cobalt forms Co(II) metaborate, which is blue in both oxidizing and reducing flames.
Chromium forms Cr(III) metaborate, which is green in both flames.
Manganese forms Mn(II) metaborate, which is amethyst (violet) in an oxidizing flame and colourless in a reducing flame.
Copper forms Cu(II) metaborate in an oxidizing flame, which is blue when cold (and green when hot). However, in a reducing flame, it is reduced to Cu(I) metaborate (colourless when hot) or metallic copper (opaque red when cold). Therefore, copper does not form a blue bead in a reducing flame.
Thus, the statement about copper salts is incorrect.
Answer: Copper salts form a blue bead when heated in a reducing flame.
Cobalt forms Co(II) metaborate, which is blue in both oxidizing and reducing flames.
Chromium forms Cr(III) metaborate, which is green in both flames.
Manganese forms Mn(II) metaborate, which is amethyst (violet) in an oxidizing flame and colourless in a reducing flame.
Copper forms Cu(II) metaborate in an oxidizing flame, which is blue when cold (and green when hot). However, in a reducing flame, it is reduced to Cu(I) metaborate (colourless when hot) or metallic copper (opaque red when cold). Therefore, copper does not form a blue bead in a reducing flame.
Thus, the statement about copper salts is incorrect.
Answer: Copper salts form a blue bead when heated in a reducing flame.