Simple molecular structures
3 marks · EasyThe table shows properties of two substances, X and Y.
| Substance | Relative molecular mass (Mr) | Physical state at room temp. | Electrical conductivity |
|---|---|---|---|
| X | 32 | gas | does not conduct |
| Y | 160 | liquid | does not conduct |
Which substance, X or Y, has the higher boiling point? Explain your answer.
Suggest why neither substance conducts electricity.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Y has the higher boiling point because it has a higher Mr, leading to stronger intermolecular forces that require more energy to overcome. · must show Correct identification of Y; explanation referencing Mr and intermolecular forces
(b) No mobile charged particles (ions or electrons) in simple molecular substances. · must show recognition of lack of mobile charge carriers
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correctly identifies Y as the substance with the higher boiling point.
M1 (a) · 1 mark · Explains this is due to higher Mr (relative molecular mass) resulting in stronger intermolecular forces.
B1 (b) · 1 mark · Mentions lack of mobile charged particles; simple molecules do not have ions/electrons free to move.
Worked solution
a) Y has the higher boiling point. This is because Y has a higher relative molecular mass (160 compared to 32), so it has stronger intermolecular forces between its molecules. More energy is required to separate these molecules, resulting in a higher boiling point.
b) Neither X nor Y conducts electricity because simple molecular substances have no charged particles (like ions or free electrons) that can move to carry current.