Investigating Oxygen in Air
This practical lesson covers:
- How to determine the approximate percentage by volume of oxygen in air using a metal or a non-metal
Investigating the percentage by volume of oxygen in air
Aim
To determine the approximate percentage by volume of oxygen in air using iron.
Background information
Air is a mixture of gases, primarily nitrogen and oxygen, with small amounts of other gases like argon and carbon dioxide. In this practical you will use the chemical property of iron, which reacts with oxygen to form iron oxide (rust), to estimate the proportion of oxygen in the air. When iron filings react with oxygen inside a sealed burette, the volume of air decreases as oxygen is used in the reaction, allowing us to measure the oxygen content by volume.
Equipment
- Burette
- Water trough
- Clamp and stand
- Deionised water
- Iron filings
Method
- Place wet iron filings inside the end of a burette. Use vaseline to make the filings stick.
- Using a clamp, stand the burette vertically over a trough of water.
- Record the starting height of the water in the burette.
- Leave for a few weeks then record the final height of the water in the burette.
- Calculate the change in height of the water in the burette. This is the volume of oxygen that was originally in the burette.
- To calculate the percentage by volume of oxygen in air, divide the change in the burette reading by the original volume of air in the burette and multiply by 100.
Aim
To determine the percentage by volume of oxygen in air using phosphorus.
Background information
Phosphorus is highly reactive and ignites easily in the presence of oxygen. In this practical, phosphorus reacts with all the oxygen in a sealed container, allowing us to measure the reduction in air volume and determine the approximate percentage of oxygen in the air.
Equipment
- Bell jar and bung
- Water trough
- Evaporating dish
- Lighter
- Deionised water
- Phosphorus
Method
- Place the phosphorus in an evaporating dish and float the dish in a trough of water.
- Ignite the phosphorus and then quickly place a bell jar into the water trough, covering the dish. Ensure there is space under the bell jar for water in the trough to move into the jar.
- Leave apparatus until the phosphorus is extinguished.
- Measure the final water level in the bell jar. The decrease in the volume of air is the volume of oxygen originally in the jar.
- Calculate the percentage of oxygen in the air using the change in water level divided by the original volume of air in the bell jar and then multiplied by 100.
Safety
- Take care when using the lighter. Run any burns under cold running water for up to 10 minutes.
- Wash hands after handling phosphorus.
- Clear any glass breakages immediately.
What is the primary purpose of this practical lesson?
to determine the exact percentage by volume of nitrogen in air using iron.
to determine the approximate percentage by volume of oxygen in air using iron.
to determine the approximate percentage by volume of nitrogen in air using iron.
to determine the exact percentage by volume of oxygen in air using iron.
|
What are the main gases present in the air?
argon and carbon helium
oxygen and helium
nitrogen and carbon monoxide
oxygen and nitrogen
|
What is the chemical property of iron used in this practical?
iron reacts with oxygen to form iron oxide.
iron reacts with carbon dioxide to form iron carbonate.
iron reacts with nitrogen to form iron nitrate.
iron reacts with argon to form iron aragonite.
|
What is the purpose of leaving the setup for a few weeks in the practical with iron?
to allow the iron filings to settle at the bottom.
to allow the water in the burette to freeze.
to allow the water in the burette to evaporate.
to allow the iron filings to react with the oxygen.
|