How can the composition of air be investigated in a lab?

The composition of air can be investigated in a lab through methods such as gas chromatography and fractional distillation.

In a laboratory setting, the composition of air can be investigated using a variety of methods. One of the most common methods is gas chromatography. This technique separates the components of a mixture based on their physical and chemical properties. A sample of air is injected into a chromatograph, which contains a column with a stationary phase. As the air sample travels through the column, different components will interact with the stationary phase to varying degrees, causing them to travel at different speeds and thus separate from each other. The separated components then exit the column and are detected, allowing for their identification and quantification.

Another method used to investigate the composition of air is fractional distillation. This process involves cooling a sample of air until it liquefies, then gradually heating it. As the temperature increases, different components of the air will boil and can be collected at different stages. For example, nitrogen, which makes up about 78% of air, boils at a lower temperature than oxygen, which makes up about 21%. Therefore, by controlling the temperature, these gases can be separated and their proportions in the air sample can be determined.

In addition to these methods, other techniques such as mass spectrometry and infrared spectroscopy can also be used to investigate the composition of air. These techniques provide more detailed information about the molecular and atomic composition of air, including the presence of trace gases and pollutants. However, they require more sophisticated equipment and are generally more complex to perform.

In all cases, safety precautions must be taken when handling gases and operating laboratory equipment. It's also important to ensure that the air sample being analysed is representative of the air in the environment, which may require taking multiple samples from different locations or at different times.