Question 60

Molar mass of the salt from $$NaBr, NaNO_3, KI$$ and $$CaF_2$$ which does not evolve coloured vapours on heating with concentrated $$H_2SO_4$$ 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)


Correct Answer: 78

Solution

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NaBr gives brown/orange vapors (Br₂) with conc H₂SO₄. KI gives violet vapors (I₂). NaNO₃ gives brown NO₂ fumes. CaF₂ does not give colored vapors (HF is colorless).

Molar mass of CaF₂ = 40 + 38 = 78 g/mol.

The answer is $$\boxed{78}$$.

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