Home / AS & A Level Chemistry 11.1 Physical properties of the Group 17 elements Exam Style Practice Questions Paper 1
Why do the halogens become less volatile as Group 17 is descended?
Correct Answer: \( \boxed{\mathrm{C}} \)
As the Group 17 elements are descended, each halogen molecule contains more electrons.
The larger electron cloud is more easily polarised, producing stronger instantaneous dipole-induced dipole (van der Waals’) forces between molecules.
As a result:
The halogen-halogen bond energy is not responsible for this trend because volatility depends on intermolecular forces, not the covalent bond within each molecule.
Therefore, the correct explanation is that the number of electrons in each molecule increases, leading to stronger van der Waals’ forces.
Hence, the correct answer is (C).
Which reduction process occurs on the surface of a catalytic converter?
Correct Answer: \( \boxed{\mathrm{C}} \)
A catalytic converter removes harmful gases from vehicle exhaust using redox reactions.
Nitrogen oxides, such as \( \mathrm{NO} \) and \( \mathrm{NO_2} \), are reduced to nitrogen gas:
\( \mathrm{2NO \rightarrow N_2 + O_2} \)
At the same time, carbon monoxide and unburnt hydrocarbons are oxidised to carbon dioxide and water.
Carbon dioxide is not reduced in the catalytic converter.
Therefore, the reduction process occurring on the catalyst is the reduction of nitrogen oxides only. Hence, the correct answer is (C).
Which graph correctly describes a trend found in Group 17?
[\(X\) represents a halogen atom.]
Correct Answer: \( \boxed{\mathrm{B}} \)
As the halogens are descended from \( \mathrm{Cl_2} \) to \( \mathrm{I_2} \), the number of electrons and the size of the electron cloud increase.
This increases the strength of the London (van der Waals’) forces between molecules, so the trend shown in graph B is correct.
The other graphs are incorrect because bond length increases (not decreases), boiling point increases (not decreases), and the bond energy of hydrogen halides decreases from HCl to HI.
Therefore, the correct answer is (B).