Cambridge O Level Chemistry · Syllabus 5070 · Chemistry of the Environment
Clean Dry Air
What is Clean Dry Air?
Air with no pollutants and with water vapour excluded from the stated composition. It is approximately 78 per cent nitrogen and approximately 21 per cent oxygen by volume, with the small remainder made up mainly of the noble gases, chiefly argon, together with carbon dioxide. Water vapour is left out because the amount present varies from place to place and from day to day.
This definition is part of the Chemistry of the Environment chapter in Cambridge O Level Chemistry.
Clean Dry Air in context
Chemistry of the environment covers water, air and carbon as three linked systems. Water is tested for presence with cobalt(II) chloride or copper(II) sulfate, and for purity with a sharp melting point of about \(0\,{}^\circ\mathrm{C}\) and boiling point of about \(100\,{}^\circ\mathrm{C}\); a domestic supply is then treated by sedimentation and filtration, carbon filtration and chlorination. Clean dry air is about 78% nitrogen and 21% oxygen, and six pollutants — carbon dioxide, carbon monoxide, particulates, methane, oxides of nitrogen and sulfur dioxide — each have a distinct source and effect, such as acid rain or global warming. Carbon dioxide absorbed in photosynthesis links combustion back to plant growth.
Common mistakes with Clean Dry Air
- “Clean air contains no carbon dioxide.” Defect Treats a normal component as a contaminant. Chemistry Carbon dioxide is part of the remainder of clean dry air. The adverse effect belongs to higher levels of it. Repair “The remainder is mainly noble gases and carbon dioxide.” Transfer What is the required wording for its effect? “Higher levels increase global warming and climate change.”