Which of the following salt on heating with concentrated H2SO4, coloured vapours do not evolve ? — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

Step 1: Heating NaBr, NaNO3, and KI with concentrated H2SO4 leads to oxidation or decomposition that releases colored gases: NaBr yields red-brown Br2 vapours, NaNO3 yields brown NO2 gas, and KI yields purple I2 vapours. Step 2: When calcium fluoride (CaF2) is heated with concentrated H2SO4, it undergo a simple acid-displacement reaction to form calcium sulfate and hydrogen fluoride (HF) gas: CaF2 + H2SO4 ---> CaSO4 + 2 HF↑. Step 3: Since HF is a colorless, pungent gas, no colored vapours are evolved during this reaction. This corresponds to option (c).