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</div><h2>HL Paper 3</h2><div class="question">
<p class="p1">Explain, in terms of their bonding, how the presence of oxygen and ozone in the ozone layer helps to prevent both higher and lower energy UV light from reaching the surface of the Earth.</p>
</div>
<br><hr><br><div class="specification">
<p class="p1">Ozone is a gas present in both the stratosphere and the troposphere.</p>
</div>
<div class="question">
<p class="p1">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.</p>
</div>
<br><hr><br><div class="question">
<p class="p1">(a) <span class="Apple-converted-space"> </span>(i) <span class="Apple-converted-space"> </span>Explain the dependence of the dissociation of diatomic oxygen, O<sub><span class="s1">2</span></sub>, and ozone, O<sub><span class="s1">3</span></sub>, on the wavelength of light.</p>
<p class="p1">(ii) <span class="Apple-converted-space"> </span>State the equations for the formation and depletion of ozone in the stratosphere by natural processes.</p>
<p class="p1">Formation of ozone:</p>
<p class="p1">Depletion of ozone:</p>
<p class="p1">(b) <span class="Apple-converted-space"> </span>(i) <span class="Apple-converted-space"> </span>State the equations for the depletion of ozone by the CFC, dichlorodifluoromethane, CCl<sub><span class="s1">2</span></sub>F<sub><span class="s1">2</span></sub>.</p>
<p class="p1">(ii) <span class="Apple-converted-space"> </span>Use your answer to part (b) (i) to explain why CFCs are so effective at ozone depletion.</p>
</div>
<br><hr><br><div class="specification">
<p>Ozone prevents UV radiation emitted from the Sun reaching the surface of the Earth.</p>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Explain, with the aid of Lewis (electron-dot) structures, the difference between oxygen and ozone in terms of the energy required to dissociate both molecules.</p>
<p> </p>
<p>Oxygen: Ozone:</p>
<div class="marks">[2]</div>
<div class="question_part_label">d.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>One CFC, Freon-13 (chlorotrifl uoromethane), which can be used as a refrigerant, has been phased out by the Montreal Protocol. Describe, using equations, the mechanism of the catalysis of ozone depletion by this particular CFC.</p>
<div class="marks">[2]</div>
<div class="question_part_label">e.</div>
</div>
<br><hr><br>