IB Chemistry HL 3.3 Electron Sharing Reactions Radicals Questions

Practise IB Chemistry HL 3.3 with HL questions on radicals, single-electron arrows and radical substitution mechanisms.

Exam points

Recognize radical species and explain homolytic fission with single-barbed arrows and initiation conditions.
Write propagation and termination equations for alkane–halogen substitution, tracking radical intermediates.

Covered syllabus points

3.3.1—Radicals 3.3.2—Homolytic fission 3.3.3—Radical substitution

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Study 3.3 Electron sharing reactions (Radicals) conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

[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]

Nitrous acid, $\mathrm{HNO}_{2}$ , is a weak acid which can be used to make acidic buffers.

Ethyl ethanoate can be produced by the reaction of ethanol with ethanoic acid. Both reactants can be synthesized from ethane through a series of reactions, the first of which is shown.

\mathrm{C}_{2} \mathrm{H}_{6}(\mathrm{~g})+\mathrm{Cl}_{2}(\mathrm{~g}) \rightarrow \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}(\mathrm{~g})+\mathrm{HCl}(\mathrm{~g})

The first step in this reaction, initiation, is given by the following equation.

\mathrm{Cl}_{2} \rightarrow 2 \mathrm{Cl} \cdot

State an essential condition for this reaction.

[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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