Question:
Aluminium trifluoride is insoluble in anhydrous HF but dissolves on addition of NaF. Aluminium trifluoride precipitates out of the resulting solution when gaseous BF3 is bubbled through. Give reasons.
Answer:
(i) HF is a covalent molecule and has strong hydrogen bonds; therefore no free fluoride ions are produced. On the other hand NaF is an ionic compound and produces free fluoride ions. These fluoride ions produced combines with AlF3 to form a soluble complex compound.
3NaF+ AlF3 → Na3 [AlF6] {Sodium hexa flouro aluminate (III)}
(ii) Aluminum trifluoride precipitates out of the resulting solution when gaseous BF3 is bubbled through because BF3 is a stronger Lewis acid than AlF3. This is because of smaller size and higher electro negativity of boron atom as compared to aluminum and therefore has more tendencies to form complexes. Therefore BF3 forms a complex of the formula Na [BF4].
Na3 [AlF6] + 3BF3→ 3Na[BF4] + AlF3.
Not what you are looking for? Go ahead and submit the question, we will get back to you.
