IB Chemistry HL 3.3 Electron Sharing Reactions Radicals Questions

Use IB Chemistry HL questions to identify radicals, explain homolytic fission and write initiation, propagation and termination steps.

Exam points

Identify radical notation and the unpaired electron, and distinguish highly reactive radicals from ions or closed-shell molecules.
Explain homolytic fission as equal electron splitting of a covalent bond, using single-barbed arrows and UV-light or heat initiation.
Write propagation steps for alkane halogenation, showing radical consumption and regeneration of the chain carrier.
Write termination by combining radicals and explain why radical substitution produces a mixture of products.

Covered syllabus points

3.3.1—Radicals 3.3.2—Homolytic fission 3.3.3—Radical substitution

[Maximum number: 2]

The Sun's energy is produced by the fusion of hydrogen nuclei.

Nuclear energy produces ionizing radiation which leads to the formation of free radicals.

Explain why free radicals are harmful to living cells.

[Maximum number: 1]

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.

Another way to make B is the reaction shown below.

State the conditions required for this reaction to occur.

[Maximum number: 4]

This question is about carbon and chlorine compounds.

(a)

Ethane, $\mathrm{C}_{2} \mathrm{H}_{6}$ , reacts with chlorine in sunlight. State the type of this reaction and the name of the mechanism by which it occurs.

Type of reaction:

Mechanism:

[ 1 ]

(b)

Formulate equations for the two propagation steps and one termination step in the formation of chloroethane from ethane.

Two propagation steps:

One termination step:

[ 3 ]

Two propagation steps:
$\mathrm{C}_{2}\mathrm{H}_{6}+\bullet\mathrm{Cl} \rightarrow \mathrm{C}_{2}\mathrm{H}_{5}\bullet+\mathrm{HCl}$ $\mathrm{C}_{2}\mathrm{H}_{5}\bullet+\mathrm{Cl}_{2} \rightarrow \mathrm{C}_{2}\mathrm{H}_{5}\mathrm{Cl}+\bullet\mathrm{Cl}$

One termination step, for example:
$\mathrm{C}_{2}\mathrm{H}_{5}\bullet+\mathrm{C}_{2}\mathrm{H}_{5}\bullet \rightarrow \mathrm{C}_{4}\mathrm{H}_{10}$

or:
$\mathrm{C}_{2}\mathrm{H}_{5}\bullet+\bullet\mathrm{Cl} \rightarrow \mathrm{C}_{2}\mathrm{H}_{5}\mathrm{Cl}$

or:
$\bullet\mathrm{Cl}+\bullet\mathrm{Cl} \rightarrow \mathrm{Cl}_{2}$

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Covered syllabus points

Question 1

Question 2

Question 3

Question (a)

Question (b)