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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 :Hydrogen fluoride (HF) is a covalent compound and has a very strong intermolecular hydrogen bonding. Thus, it does not provide ions and <a href="https://interviewquestions.tuteehub.com/tag/aluminium-858823" style="font-weight:bold;" target="_blank" title="Click to know more about ALUMINIUM">ALUMINIUM</a> fluoride (AlF) does not <a href="https://interviewquestions.tuteehub.com/tag/dissolve-432057" style="font-weight:bold;" target="_blank" title="Click to know more about DISSOLVE">DISSOLVE</a> in it.<br/> Sodium fluoride (NaF) is an ionic compound and when it is added to the mixture, AlF dissolves. This is because of the availability of free `F^-`. The reaction involved in the <a href="https://interviewquestions.tuteehub.com/tag/process-11618" style="font-weight:bold;" target="_blank" title="Click to know more about PROCESS">PROCESS</a> is : <br/>`3NaF+ AlF_3 to underset"Soluble complex"(Na_3 [AlF_6])` <br/> When boron trifluoride `(BF_3)` is added to the solution, aluminium fluoride precipitates out of the solution. This happens because the tendency of boron to form complexes is <a href="https://interviewquestions.tuteehub.com/tag/much-2164829" style="font-weight:bold;" target="_blank" title="Click to know more about MUCH">MUCH</a> more than that of aluminium. Therefore, when `BF_3` is added to the solution, <a href="https://interviewquestions.tuteehub.com/tag/b-387190" style="font-weight:bold;" target="_blank" title="Click to know more about B">B</a> replaces Al from the complexes according to the following reaction. <br/> `Na_3[AlF_6] 3BF_3 to underset"Soluble complex"(3Na[BF_6])+ underset"Precipitate"(AlF_3)`</body></html>


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