Question

Taking hydrogen peroxide, how would you prepare oxygen in the laboratory?

Answer 1

We prefer hydrogen peroxide $({H_2}{O_2})$ for lab preparation of oxygen in the laboratory with the help of a catalyst, manganese dioxide $(Mn{O_2})$. The gas is produced and water is collected by downward displacement. We use ${H_2}{O_2}$ to prepare oxygen gas in the lab because there is no heating required and the rate of evolution of oxygen $({O_2})$ is moderate and under control. And also, hydrogen peroxide $({H_2}{O_2})$ is a safe chemical.

Complete step by step answer:
Oxygen can be made from hydrogen peroxide $({H_2}{O_2})$ that will decompose slowly to form water and oxygen gas:
hydrogen peroxide $\to$ water + oxygen
$2{H_2}{O_2}\xrightarrow{{Mn{O_2}}}2{H_2}O + {O_2}$
The rate of reaction can be increased using a catalyst, manganese dioxide. When manganese dioxide is added to hydrogen peroxide, oxygen bubbles are produced.
To make oxygen in the laboratory, hydrogen peroxide is poured drop by drop into a round bottom flask containing some manganese dioxide $(Mn{O_2})$. The rate of reaction can be increased using a catalyst, manganese dioxide $(Mn{O_2})$. The gas which is produced is collected in an upside-down gas jar filled with water. As the oxygen collects in the top of the gas jar, it pushes the water out, that is there is downward displacement of water.
Instead of the gas jar and water bath, we could use a gas syringe to collect the oxygen.

Note: Since the water is displaced downward by the gas collecting in the jar, therefore this process is called downward displacement of water and the reasons are:
A.Oxygen is only slightly soluble in water and therefore we can collect over water without fear of excessive dilution.
B.Oxygen which is slightly heavier than air cannot be collected over air.