Question

Which of the following does not give a borax-bead test?
(a) Ferrous salt
(b) Chromium
(c) Cobalt
(d) Sodium

Answer 1

Hint Since the borax-bead test is used for identification of transition metals, only coloured metals give this test, while colourless ions don’t. Now, this information can be used to answer the given question.

Complete step by step answer:
- Borax-bead test is known to disclose the presence of transition metals in a sample. In this test, the oxides of metals produce characteristic colours when exposed to a burner flame.
- A clear glassy bead of borax fused in a wire loop will react chemically with the salts of metals and yield colours that help to recognize the metal.
- For example, manganese compounds produce a violet bead, and cobalt produces a deep blue bead colour.
- It is safe that compounds containing colourless ions do not show borax-bead test.
- Ferrous salt, chromium, and cobalt have coloured ions. Whereas, sodium has colourless ions.

Therefore, the answer to the above question is option (D) Sodium.

Note: As we heat borax on a hot loop of platinum wire, it swells up to form a transparent colourless glassy bead. When we bring this hot bead in contact with a certain amount of coloured salt and heat it again, the bead then acquires a characteristic colour. This colour of the bead is useful to determine the type of cation present.