DP Chemistry (last assessment 2024)
Question 19M.3.hl.TZ1.d(i)
| Date | May 2019 | Marks available | [Maximum mark: 3] | Reference code | 19M.3.hl.TZ1.d(i) |
| Level | hl | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | d(i) | Adapted from | N/A |
d(i).
[Maximum mark: 3]
19M.3.hl.TZ1.d(i)
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]
Markscheme
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 [✔]
Examiners report
Many candidates scored the first mark for stating that methane is tetrahedral. Further details to explain how methane absorbs IR radiation were generally insufficient. Many candidates referred to “dipole movements” despite dipole moment being in the stem of the question.
