| Date | May 2012 | Marks available | 3 | Reference code | 12M.3.hl.TZ1.E1 |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | E1 | Adapted from | N/A |
Question
Ozone is a gas present in both the stratosphere and the troposphere.
Oxygen absorbs much of the ultraviolet (UV) radiation from the sun, but ozone is important because it absorbs UV radiation not absorbed by oxygen. Explain, referring to the bonding in the two molecules, why this is the case.
Markscheme
oxygen has double bond/bond order 2;
ozone has delocalized bond/bond order 1.5;
oxygen bond/bond in oxygen (molecule) is stronger/shorter / ozone bond is weaker/longer;
ozone absorbs light of lower energy/lower frequency/longer wavelength;
Accept suitable diagram.
Examiners report
Most candidates were aware of the difference in bonding between diatomic oxygen and ozone, and the effect this has on the UV frequencies they absorb.
