Gases in the Atmosphere: Answers

Which gases are found in the atmosphere and in what proportions?

The atmosphere is predominantly made up of nitrogen (78%) and oxygen (21%) with small amounts of argon (0.9%), carbon dioxide (0.04%) and various other gases (0.06%).

Describe two methods in which we can determine the percentage of oxygen in air experimentally.

One method is to place a metal, such as a ball of iron wall inside an upturned measuring cylinder standing in a beaker of water. The total volume of air is measured then the experiment is left for a few hours to allow all of the oxygen in the air to react with the iron, forming iron oxide. When the volume of air stops decreasing, the new volume is measured. The difference in volumes will be the volume of oxygen that has reacted. We can calculate the percentage of oxygen in the air by dividing the difference in volume by the start volume and multiplying by 100.

An alternative method is to place a non-metal, such as phosphorous in between two gas syringes. The first syringe is used to push air over the phosphorous. Any oxygen in the air will react with the phosphorous to form phosphorous oxide. The second syringe collects the remaining air. The difference in volumes in the first and second syringes is equal to the oxygen that has reacted. We use the same calculation as in the previous experiment to determine the percentage of oxygen in air.

Write the equation for the reaction of sulfur with oxygen. What environmental impact does this product have?

Sulfur dioxide gas reacts with water vapour to form acid rain. Acid rain increases the pH of ponds and lakes, making it difficult for aquatic life to survive. It also destroys limestone buildings and statues.

Write a word and symbol equation (including state symbols) for the thermal decomposition of calcium carbonate. What environmental impact does the gaseous product have?

Carbon dioxide is a greenhouse gas which means it contributes to global warming. It traps reflected heat in the atmosphere, resulting in a gradual increase in the Earth’s temperature.

How have human activities increased the amount of carbon dioxide in the atmosphere?

Deforestation and burning fossil fuels have increased the amount of carbon dioxide in the atmosphere.

What are the consequences of global warming?

Global warming is causing the ice caps to melt, leading to flooding and the destruction of habitats. It also increases the frequency of extreme weather events, such as droughts, cyclones and hurricanes.