Question

Layer test is associated with:
(A) Chloroform
(B) Pyrene
(C) Bromine
(D) Wood alcohol

Answer 1

Hint: Organic Layer test is a test involving redox reactions among halides. Using this information try to identify the correct option.

Complete step by step solution:
The organic Layer test is a test involving redox reactions among halides. This test is used to detect the presence of bromide ions and iodide ions in a solution (e.g., Lassaigne’s test solution). The layer test is carried out by adding an organic solvent such as carbon disulphide or chloroform in the presence of nitric acid and chlorine water to the given solution. For example, Lassaigne’s extract is acidified with dilute nitric acid($HNO_3$) and chlorine water is added to it. When the organic solvent is added to this aqueous solution and shaken the mixture vigorously but carefully, the liberated bromine or iodine liberated by the redox reaction of bromide or iodide ions with chlorine) would travel to the organic layer to give distinguished colour. In case bromine ion is present, it will give an orange layer while in case iodine ion is present, it will give a violet layer. The key is bromine and iodine are much soluble in organic solvents than in water. Since we are using chlorine as an oxidant, chloride ions are negated here.

So, the correct answer is option c) The Layer test is associated with bromine $Br_2$.

Additional information:
This is an old school test, it was popular and a widely used test a few decades ago, it is not so commonly used under current modern laboratory conditions. The tests are replaced by tests which are more controlled, faster to perform and also work of Chlorine simultaneously

Note: The $Br^{-}$ ion and $I^{-}$ ions do give the layer test but the $Cl_2$ is not identified by this test. Chlorine is almost colourless, it is gas, it will not be visible in these chlorinated solvents. And above all, very few oxidizing agents can form chlorine with chloride.