A white solid gives a green residue on being subjected to the cobalt nitrate test. On being warmed with concentrated H2SO4, the solid gives a brown gas, which evolves vigorously on the addition of Cu

Question

A white solid gives a green residue on being subjected to the cobalt nitrate test. On being warmed with concentrated H2SO4, the solid gives a brown gas, which evolves vigorously on the addition of Cu turnings. The solid may be:

Prashant Kotian · Accepted Answer

Correct answer: A. Step 1: A green residue in the cobalt nitrate test indicates the presence of zinc (Zn2+) as it forms Rinmann's green. Step 2: On heating with concentrated H2SO4, nitrate salts release nitric acid, which decomposes to brown nitrogen dioxide (NO2) gas. Adding Cu turnings reduces the nitrate/nitric acid to liberate more brown NO2 gas vigorously. Step 3: Therefore, the white solid containing zinc and nitrate is zinc nitrate, Zn(NO3)2, matching option (a).

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