IB Chemistry SL 3.4.6 Lewis Acid Base Theory Questions

Use real SL exam questions to distinguish Lewis acids from Lewis bases, locate the donated pair and classify the roles of nucleophiles and electrophiles.

Exam points

Define and classify Lewis acids as electron-pair acceptors and Lewis bases as electron-pair donors, distinguishing them from Brønsted–Lowry definitions.
Identify the specific electron pair or lone pair and the electron-deficient atom or species that accepts it in a Lewis acid-base example.
Relate nucleophiles to Lewis bases and electrophiles to Lewis acids in a stated reaction or complex-ion context, identifying each role.

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Study 3.4.6—Lewis acid-base theory conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

[Maximum number: 4]

The element boron has two naturally occurring isotopes, ${ }^{10} \mathrm{~B}$ and ${ }^{11} \mathrm{~B}$ .

(a)

Define an acid according to the Lewis theory.

[ 1 ]

(b)

State and explain the acid-base character of $\mathrm{NH}_{3}$ and $\mathrm{BF}_{3}$ according to the Lewis theory.

[ 3 ]

$N H_{3}$ : Lewis base;
$B F_{3}$ : Lewis acid;
$\mathrm{NH}_{3}$ has non-bonding/lone pair of electrons and $\mathrm{BF}_{3}$ has only 3 pairs of electrons around B / incomplete octet;

Reference to outer electrons of N and B is needed for the mark.

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IB Chemistry SL 3.4.6 Lewis Acid Base Theory Questions question 1

Question (a)

Question (b)