| Date | May 2013 | Marks available | 3 | Reference code | 13M.3.hl.TZ1.E1 |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Describe | Question number | E1 | Adapted from | N/A |
Question
Increasing concentrations of greenhouse gases are considered to cause global warming. Ozone depletion is another environmental concern.
Ozone and oxygen are in equilibrium in the stratosphere. Both gases absorb ultraviolet radiation and dissociate producing oxygen atoms.
Describe the dependence of ozone and oxygen dissociation on the wavelength of radiation absorbed, and explain how this is related to the bonding in each molecule.
Markscheme
ozone depletion requires higher wavelength / oxygen dissociation requires lower wavelength;
M1 must refer to wavelength.
wavelength inversely proportional to energy / wavelength increases as energy decreases;
oxygen has double bond/bond order of 2 and ozone has bond order of 1.5/intermediate bond between single and double;
Stating that ozone has resonance or delocalization alone is not sufficient.
ozone weaker bond / O–O bond energy in ozone lower;
Accept opposite argument of oxygen for M4.
Examiners report
(c) was well answered.
