General Chemistry: Principles and Modern Applications (10th Edition)

Published by Pearson Prentice Hal
ISBN 10: 0132064529
ISBN 13: 978-0-13206-452-1

Chapter 21 - Chemistry of the Main-Group Elements I: Groups 1, 2, 13, and 14 - 21-9 Concept Assessment - Page 951: 21-9


The electron deficiency in $ \mathrm{AlF_3}$ explains its high insolubility, but it forms $\left[\mathrm{AlF}_{4}\right]^{-}$ in the presence of $\mathrm{F}^{-}$ from $\mathrm{KF}$, which facilitates the solubility. On the other hand, $\mathrm{BF}_{3}$ is a stronger Lewis acid than $ \mathrm{AlF_3}$ and abstracts a $\mathrm{F}^{-}$ ion from $\left[\mathrm{AlF}_{4}\right]^{-}$, yielding the formation of the insoluble $ \mathrm{AlF_3}$ once again as foolows: $\left[\mathrm{AIF}_{4}\right]^{-}+\mathrm{BF}_{3} \longrightarrow \mathrm{AlF}_{3}(\mathrm{s})+\left[\mathrm{BF}_{4}\right]^{-}$

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