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One of the questions I found in an NCERT book. Interestingly I could not find the answer anywhere on the internet. Hence, stack exchange.

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closed as unclear what you're asking by Tyberius, Mithoron, Mathew Mahindaratne, Jon Custer, tschoppi Jul 11 at 5:54

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ Welcome to ChemSE. Please substantiate your question by addition of futher information providing (chemical) context + at least the start of your argumentation to solve the question. Layer of what? Since NCERT is an organisation, would it be a question about organic chemistry or inorganic chemistry or something else? $\endgroup$ – Buttonwood Jul 10 at 18:02
  • $\begingroup$ @Buttonwood The organization NCERT writes textbooks for Indian schools which are colloquially called NCERT books, and the chemistry textbook contains organic, physical and inorganic chemistry together. And BTW I haven't come across this "Layer test" ever in it, but again I never read the book seriously. $\endgroup$ – William R. Ebenezer Jul 10 at 18:12
  • $\begingroup$ @Soham can you type out how the "Layer test" described in the book? Some chemical context is mandatory. I can't find anything by that name anywhere. $\endgroup$ – William R. Ebenezer Jul 10 at 18:14
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The so called layer test is a qualitative analysis of bromide and iodide salts (old school chemistry). The salts are oxidized in water and then chloroform or carbon tetrachloride is added. This forms a layer. Since the partition coefficient of iodine or bromine is much higher for the organic solvent, a colored layer is formed sitting in the bottom of the test tube (hence the name layer test). Bromine shows an orange color and iodine shows a beautiful violet color. Chlorine is almost colorless, it is a gas, it will not be visible in these chlorinated solvents. And above all, very few oxidizing agents can form chlorine with chloride.

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Organic Layer test is a test involving redox reactions among halides. This test is used to detect in the presence of bromide ions and iodide ions in a solution (e.g., Lassaigne’s test solution). Layer test is carried out by adding 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 and chlorine water is added to it. When organic solvent is added to this aqueous solution and shaken the mixture vigorously but carefully, the liberated bromine or iodine liberated by redox reaction of bromide or iodide ions with chlorine) would be traveled to organic layer to give distinguished color. In case bromine is present, it will give an orange layer while it will give a violet layer in case of presence of Iodine. Relevant redox reactions are given below:

$$\ce{Br- + Cl2 -> Br2 + Cl-}$$ $$\ce{I- + Cl2 -> I2 + Cl-}$$

The key is bromine and iodine are much soluble in organic solvents than in water. Since we are using chlorine as a oxidant, chloride ions are negated here.

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