IB Chemistry HL 3.3 Electron Sharing Reactions Question Bank

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

[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 ]

substitution AND «free-»radical

OR

substitution AND chain

Marking guidance:

Award [1] for "«free-»radical substitution" or "S ${ }_{R}$ " written anywhere in the answer.

(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

3.3 Electron sharing reactions (Radicals) question 1

3.3 Electron sharing reactions (Radicals) question 2

3.3 Electron sharing reactions (Radicals) question 3

Question (a)

Question (b)