Summary and Exam Tips for Gases in the Atmosphere
Gases in the Atmosphere is a subtopic of Inorganic Chemistry, which falls under the subject Chemistry in the Edexcel IGCSE curriculum. The atmosphere's composition has remained relatively stable for 200 million years, consisting of approximately 80% nitrogen and 20% oxygen, with trace amounts of carbon dioxide, water vapor, and noble gases. Historical atmospheric compositions are studied through air bubbles in polar ice cores. Common air pollutants include carbon monoxide, sulfur dioxide, oxides of nitrogen, carbon dioxide, and methane.
To determine the percentage of oxygen in the air, a reaction involving a metal or non-metal, such as burning phosphorus in a bell jar, is used. This experiment measures water level changes to calculate oxygen content, though phosphorus's toxicity requires careful handling. Combustion involves oxygen reacting with elements or compounds to form oxides, releasing heat in exothermic reactions. Key reactions include magnesium forming magnesium oxide, hydrogen producing water, and sulfur yielding sulfur dioxide.
Thermal decomposition of metal carbonates, like copper(II) carbonate, produces metal oxides and carbon dioxide, which can be tested with limewater. The greenhouse effect involves greenhouse gases like carbon dioxide, methane, and water vapor trapping heat, contributing to the enhanced greenhouse effect and climate change.
Exam Tips
- Understand the Composition: Remember the proportions of nitrogen and oxygen in the atmosphere and the role of trace gases.
- Pollutants Identification: Be able to list and describe common air pollutants and their effects.
- Oxygen Measurement: Familiarize yourself with the phosphorus experiment for determining oxygen percentage and its safety precautions.
- Combustion Reactions: Know the combustion reactions of magnesium, hydrogen, and sulfur, including their chemical equations.
- Greenhouse Effect: Understand how greenhouse gases trap heat and the implications of the enhanced greenhouse effect on climate change.
