Oxygen gas can be collected for analysis through two primary methods: the decomposition of hydrogen peroxide and the electrolysis of water.

Decomposition of Hydrogen Peroxide

One of the most common ways to collect oxygen gas is through the decomposition of hydrogen peroxide ($\text{H}_2\text{O}_2$). This straightforward process requires the addition of a catalyst, such as manganese dioxide ($\text{MnO}_2$). The catalyst accelerates the reaction, causing hydrogen peroxide to decompose into water ($\text{H}_2\text{O}$) and oxygen gas ($\text{O}_2$). The overall reaction can be represented as:

The oxygen gas generated can then be collected over water in a gas jar or a suitable container.

Electrolysis of Water

Another effective method for generating oxygen gas is through the electrolysis of water. This process involves passing an electric current through water, which causes it to decompose into hydrogen and oxygen gases. The gases are produced at different electrodes: hydrogen is generated at the cathode (the negative electrode), while oxygen is produced at the anode (the positive electrode). The reaction can be represented as:

The oxygen gas can be collected directly at the anode.

Gas Collection Techniques

In both methods, it is crucial to collect the gas without any contamination. This can be accomplished by using a delivery tube to direct the gas into a gas jar or another container. To ensure purity, the container should be filled with water and inverted in a trough of water. As the gas is collected, it displaces the water, a technique known as “collecting gas over water.” This method helps ensure that the oxygen collected is free from impurities and ready for subsequent testing.

Safety Precautions

Safety is of utmost importance when conducting these experiments. Always wear safety goggles and lab coats, and handle all chemicals with caution. Following proper safety protocols is essential to ensure a safe laboratory environment.