International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

What is the test for oxygen gas?

1. Use a glowing splint and see if it relights

2. Bubble the gas through limewater

3. Use a litmus paper to check acidity

4. Heating the gas until it burns

The correct answer is: Use a glowing splint and see if it relights

The test for oxygen gas involves using a glowing splint, which is a wooden stick that has been ignited and then extinguished so that it is still hot but does not have an active flame. When the glowing splint is introduced into a container of oxygen, the increased concentration of this gas allows for combustion to occur. Hence, if the splint relights, it confirms the presence of oxygen. This method is effective because oxygen supports combustion, so the glowing splint's reaction demonstrates the gas's ability to facilitate the burning process. This characteristic distinguishes oxygen from other gases that do not support combustion. The other methods mentioned, such as bubbling the gas through limewater, are associated with different gases; for example, limewater tests for carbon dioxide by turning milky. Litmus paper checks for acidity and is not specific to any particular gas. Heating the gas until it burns is not a typical test for oxygen itself, as it can produce a variety of reactions and does not provide the distinct indication that a glowing splint does.