IB Chemistry SL 3.4 Electron Pair Sharing Reactions Questions

Use IB Chemistry SL questions to identify electron-pair donors and acceptors, draw curly-arrow mechanisms and predict organic products.

Exam points

Identify electron-rich nucleophiles and electron-deficient electrophiles, and classify Lewis bases and Lewis acids by the electron pair they donate or accept.
Show heterolytic fission with a full double-barbed curly arrow, assigning the correct positive and negative ionic fragments and distinguishing it from homolysis.
Deduce nucleophilic substitution products by replacing the leaving group, preserving the carbon skeleton and drawing curly arrows from the electron pair source.
Explain electrophilic attack on an alkene π bond, write addition equations with water, halogens or hydrogen halides, and determine the product connectivity.

Covered syllabus points

3.4.1—Nucleophiles 3.4.2—Nucleophilic substitution 3.4.3—Heterolytic fission 3.4.4—Electrophiles 3.4.5—Electrophilic addition to alkenes 3.4.6—Lewis acid-base theory 3.4.7—Coordination bond formation 3.4.8—Complex ions

[Maximum number: 3]

Chlorine undergoes many reactions.

(a)

Predict, giving a reason, whether ethane or chloroethane is more reactive.

[ 1 ]

chloroethane AND C-Cl bond is weaker/ $324 \mathrm{~kJ} \mathrm{~mol}^{-1}$ than C-H bond $/ 414 \mathrm{~kJ} \mathrm{~mol}^{-1}$

OR

chloroethane AND contains a polar bond

Marking guidance:

Accept "chloroethane AND polar".

(b)

Write the equation for the reaction of chloroethane with a dilute aqueous solution of sodium hydroxide.

[ 1 ]

$\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Cl}(\mathrm{l})+\mathrm{OH}^{-}(\mathrm{aq}) \rightarrow \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}(\mathrm{aq})+\mathrm{Cl}^{-}(\mathrm{aq})$

OR
$\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Cl}(\mathrm{l})+\mathrm{NaOH}(\mathrm{aq}) \rightarrow \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}(\mathrm{aq})+\mathrm{NaCl}(\mathrm{aq})$

Marking guidance:

Accept use of $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}$ and $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH} / \mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}$ in the equation.

(c)

Deduce the nucleophile for the reaction in d(iii).

[ 1 ]

hydroxide «ion»/ $\mathrm{OH}^{-}$

Marking guidance:

Do not accept NaOH.

[Maximum number: 1]

Which row correctly shows heterolytic fission?

Original rows A–D showing Br–Br bond fission.

Row A

Row B

Row C

Row D

[Maximum number: 1]

Which species is the electrophile?

\mathrm{CH}_{3} \mathrm{Br}+\mathrm{OH}^{-} \rightarrow \mathrm{CH}_{3} \mathrm{OH}+\mathrm{Br}^{-}

$\mathrm{OH}^{-}$

$\mathrm{Br}^{-}$

$\mathrm{CH}_{3} \mathrm{OH}$

$\mathrm{CH}_{3} \mathrm{Br}$

[Maximum number: 1]

Chlorine undergoes many reactions.

Deduce the nucleophile for the reaction in d(iii).

hydroxide «ion»/ $\mathrm{OH}^{-}$

Marking guidance:

Do not accept NaOH.

[Maximum number: 3]

Alkenes, such as A (shown below), are important intermediates in the petrochemical industry because they undergo addition reactions to produce a wide variety of products, such as the conversion shown below.

(a)

State the reagent required to convert A into B.

[ 1 ]

(b)

A can also be converted into C without going via B. State the reagent and conditions required.

[ 2 ]

water / steam; ..... [2]
heat and acid catalyst /(concentrated) $\mathrm{H}_{2} \mathrm{SO}_{4} / \mathrm{H}_{3} \mathrm{PO}_{4}$ ;

[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.

[Maximum number: 1]

Peptidase enzyme in the digestive system hydrolyses peptide bonds.

Outline how lead ions could be removed from an individual suffering from lead poisoning.

«use of» host-guest chemistry

OR

chelation «therapy»

Marking guidance:

Accept specific medication/chelating agent such as EDTA, $\ce{CaNa2}$ EDTA, succimer, D-penicillamine, dimercaprol.

All question bank results loaded

Covered syllabus points

Question 1

Question (a)

Question (b)

Question (c)

Question 2

Question 3

Question 4

Question 5

Question (a)

Question (b)

Question 6

Question (a)

Question (b)

Question 7