Preparing Oxygen and Forming Oxides
Oxygen can be prepared, collected, identified, and studied through carefully controlled oxidation reactions.
1. Laboratory preparation of oxygen
A convenient laboratory reaction is catalytic decomposition of hydrogen peroxide:
Manganese dioxide, \(MnO_2\), is a catalyst: it increases the reaction rate but is regenerated rather than consumed overall. It is written above the arrow and is not added as a reactant coefficient. The reaction is decomposition because one compound forms more than one product.
Oxygen is only slightly soluble in water and does not react rapidly with water at ordinary conditions, so it can be collected by displacement of water. A delivery tube carries the gas into an inverted water-filled jar. Oxygen bubbles rise into the jar and push water out. The first portion of gas may contain air from the apparatus and is not used for the test.
2. Physical properties and identification
At ordinary conditions oxygen is a colorless, odorless gas. It is slightly denser than air and only slightly soluble in water. A glowing splint placed into a collected oxygen sample relights because oxygen strongly supports combustion. This is evidence for oxygen, but unknown gases must never be tasted or deliberately inhaled.