An unknown salt M, when gently heated with concentrated H2SO4 and K2Cr2O7, produces reddish-brown vapours X. These vapours, when passed into NaOH solution, give a yellow solution Y. Yellow precipitate Z is formed on adding Pb(OAc)2 in acetic acid to Y. Based on this reaction scheme, the sa

Question

An unknown salt M, when gently heated with concentrated H2SO4 and K2Cr2O7, produces reddish-brown vapours X. These vapours, when passed into NaOH solution, give a yellow solution Y. Yellow precipitate Z is formed on adding Pb(OAc)2 in acetic acid to Y. Based on this reaction scheme, the salt(s) M could be:

Accepted Answer

NaBr. X is Br2 (reddish-brown vapour). Br2 + NaOH -> NaBr + NaBrO3 (yellow solution Y). NaBrO3/NaBr + Pb(OAc)2 -> PbBr2 (yellow precipitate Z). This is the bromine test. So M must be a bromide salt: NaBr (option C). NH4Cl+NaBr mixture would also give Br2, but the primary salt listed is NaBr. AgCl has no bromine; Ca(ClO4)2 has no bromine.

Solution

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