Molar mass of the salt from $\mathrm{NaBr}, \mathrm{NaNO}_{3}, \mathrm{KI}$ and $\mathrm{CaF}_{2}$ which does not evolve coloured vapours on heating with concentrated $\mathrm{H}_{2} \mathrm{SO}_{4}$ is \_\_\_\_ $\mathrm{g} \mathrm{mol}^{-1}$, (Molar mass in $\mathrm{g} \mathrm{mol}^{-1}$: $\mathrm{Na}: 23, \mathrm{~N}: 14, \mathrm{~K}: 39$, $\mathrm{O}: 16, \mathrm{Br}: 80, \mathrm{I}: 127, \mathrm{~F}: 19, \mathrm{Ca}: 40$

JEE Main · 2024 · 31 Jan 2024 · Shift 1 · Practical and Analytical Chemistry

Molar mass of the salt from

NaBr, NaNO_{3}, KI

and

CaF_{2}

which does not evolve coloured vapours on heating with concentrated

H_{2} SO_{4}

is ____

g mol^{- 1}

, (Molar mass in

g mol^{- 1}

Na : 23, N : 14, K : 39

O : 16, Br : 80, I : 127, F : 19, Ca : 40

Answer: 78

Solution

On heating with concentrated

H_{2} S O_{4}

NaBr

evolves reddish-brown

B r_{2}

vapour,

NaN O_{3}

evolves brown

N O_{2}

, and

KI

evolves violet

I_{2}

vapour.

Ca F_{2}

, however, releases only colourless HF gas -- no coloured vapour.

Molar mass of

Ca F_{2} = 40 + 2 (19) = 78 g mo l^{- 1}

JEE Main · 2024 · 31 Jan 2024 · Shift 1 · Integer answer

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