Molar mass of the salt from NaBr, NaNO₃, KI and CaF₂ which does not evolve coloured vapours on heating with concentrated H₂SO₄ is _____

Salt Not Giving Coloured Vapours with Conc H2SO4 | JEE Mains PYQ | Mole Concept

Q. Molar mass of the salt from NaBr, NaNO₃, KI and CaF₂ which does not evolve coloured vapours on heating with concentrated H₂SO₄ is ______ g mol⁻¹.

( Molar mass in g mol⁻¹ : Na : 23, N : 14, K : 39, O : 16, Br : 80, I : 127, Ca : 40, F : 19 )

Explanation

Step 1: Behaviour with concentrated H₂SO₄

NaBr and KI evolve coloured vapours (Br₂ – brown, I₂ – violet). Hence, both are eliminated.

Step 2: Check remaining salts

NaNO₃ gives nitric acid vapours (colourless). CaF₂ gives HF gas (colourless).

Step 3: Salt that does not evolve coloured vapours

NaNO₃ is selected.

Step 4: Calculate molar mass of NaNO₃

Na = 23
N = 14
O₃ = 16 × 3 = 48

Total molar mass = 23 + 14 + 48 = 85 g mol⁻¹

Correct Answer = 78

Previous Year Questions – Mole Concept

A solution of H2SO4 is 31.4% H2SO4 by mass and has a density of 1.25 g/mL. The molarity of the H2SO4 solution is ______ M (nearest integer).