11.16.    Aluminium trifluoride is insoluble in anhydrous H\! F but dissolves on addition of N\! aF. Aluminium trifluoride precipitates out of the resulting solution when gaseous  B\! F_{3}  is bubbled through. Give reasons.

Answers (1)
M manish

H\! F is a covalent compound and has a very strong intermolecular hydrogen bonding. So, it does not provide any ions, as a result, AlF_{3} does not dissolve int it. N\! aF is an ionic compound and it can give F^{-} ions. Thus AlF_{3} can dissolve in it and form Na_{3}[AlF_{6}]

AlF_{3}+3NaF\rightarrow Na_{3}[AlF_{6}] (sodium hexafluoroaluminate(III))

When B\! F_{3} is added to the solution, it can replace aluminium and formed a complex of itself and AlF_{3} can precipitate out.

Na_{3}[AlF_{6}]+BF_{3}\rightarrow 3Na[BF_{4}]+AlF_{3}

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