Question 19M.3.sl.TZ1.d(i)
| Date | May 2019 | Marks available | [Maximum mark: 3] | Reference code | 19M.3.sl.TZ1.d(i) |
| Level | sl | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | d(i) | Adapted from | N/A |
Natural gas is an energy source composed mainly of methane.
Explain how methane absorbs infrared (IR) radiation by referring to its molecular geometry and dipole moment.
[3]
methane is tetrahedral
OR
methane has zero dipole moment/is non-polar/bond polarities cancel [✔]
Any two of:
IR absorption can result in increased vibrations/bending/stretching [✔]
only modes that cause change in dipole absorb IR [✔]
for methane this is asymmetric bending/stretching [✔]
Comprehensive answers were rare. Many students gained a mark for correct statements about methane’s molecular geometry or polarity, though quite a few totally disregarded the instruction to refer to these. Some seemed aware of the link to vibrational motion and the better ones also identified the need for a change in dipole moment.
