Question:

Identify the pair containing only Lewis acids.

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Lewis acids accept electron pairs, while Lewis bases donate electron pairs. \(H^+\) and \(BF_3\) are common Lewis acids.
  • \(BF_3,\ NH_3\)
  • \(H^+,\ BF_3\)
  • \(F^-,\ H_2O\)
  • \(NH_4^+,\ NH_3\)
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The Correct Option is B

Solution and Explanation

A Lewis acid is a species which can accept a pair of electrons. A Lewis base is a species which can donate a pair of electrons. Now check the options carefully. The species \(BF_3\) is electron deficient because boron has only six electrons around it after bond formation. So, \[ BF_3 \] can accept an electron pair. Therefore, \[ BF_3 \] is a Lewis acid. Now consider: \[ H^+. \] The hydrogen ion has no electron and can accept an electron pair from a donor species. Therefore, \[ H^+ \] is also a Lewis acid. So the pair \[ H^+,\ BF_3 \] contains only Lewis acids. On the other hand, \[ NH_3 \] has a lone pair on nitrogen and donates this lone pair. Therefore, \[ NH_3 \] is a Lewis base, not a Lewis acid. Hence, the correct pair containing only Lewis acids is: \[ H^+,\ BF_3. \]
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