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Aluminium trifluoride is insoluble in anhydrous HF but dissolves on addition of NaF. Aluminium trifluoride precipitates out of the resulting solution when gaseous BF_(3) is bubbled through. Give reasons.

Answer» <html><body><p></p>Solution :AlF3 does not dissolve in anhydrous HF because HF is a covalent compound and is strongly <a href="https://interviewquestions.tuteehub.com/tag/hydrogen-22331" style="font-weight:bold;" target="_blank" title="Click to know more about HYDROGEN">HYDROGEN</a> bonded. NaF is an ionic compound and provides `F^-` <a href="https://interviewquestions.tuteehub.com/tag/ions-1051295" style="font-weight:bold;" target="_blank" title="Click to know more about IONS">IONS</a> which combine with `AlF_3` to form a soluble complex, `Na_3 [AlF_6]`. Therefore, `AlF_3` <a href="https://interviewquestions.tuteehub.com/tag/dissolves-956402" style="font-weight:bold;" target="_blank" title="Click to know more about DISSOLVES">DISSOLVES</a> in presence of NaF. <br/>`3NaF + AlF_3 to underset("Sodium hexafluoroaluminate (III)")(Na_3 [ AlF_6])` <br/>When gaseous `BF_3` is bubbled through the <a href="https://interviewquestions.tuteehub.com/tag/resulting-1187445" style="font-weight:bold;" target="_blank" title="Click to know more about RESULTING">RESULTING</a> solution, boron because of its smaller size and higher electronegativity, enters into the complex and expels aluminium. Thus, `AlF_3`gets precipitated.<br/>`Na_3 [AlF_6] + 3BF_3 to underset("Sod. <a href="https://interviewquestions.tuteehub.com/tag/tetrafluoroborate-1243182" style="font-weight:bold;" target="_blank" title="Click to know more about TETRAFLUOROBORATE">TETRAFLUOROBORATE</a> (III) (soluble)")(3Na[BF_4]) + underset("insoluble")(AlF_3) darr`</body></html>


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