Question

How is oxygen prepared in laboratory?

Answer 1

Laboratory preparation of oxygen

• The easiest method of preparing oxygen in the laboratory is by the slow decomposition of hydrogen peroxide solution $\left({\mathrm{H}}_2{\mathrm{O}}_2\right)$using manganese dioxide $\left({\mathrm{MnO}}_2\right)$as a catalyst.
• A small quantity of black manganese dioxide is taken in a round-bottom flask.
• In one of the holes, a thistle funnel with a stopper is fitted and through the other hole, a delivery tube is introduced.
• Hydrogen peroxide is added to the flask drop by drop with the help of a thistle funnel.
• The other end of the delivery tube passes into a beehive shelf placed in a water trough.
• Manganese dioxide decomposes hydrogen peroxide very fast and liberates oxygen.
• Oxygen passes through the delivery tube and bubbles out of the water in the trough.
• The first few bubbles of the gas are allowed to escape into the air.
• Then an inverted gas jar full of water is placed over the beehive shelf.
• Oxygen gets collected in the jar by downward displacement of water.
• As oxygen keeps collecting in the gas jar, the water level in the jar keeps on decreasing and the space above the water gets filled with oxygen.
• When all the water has been displaced, the gas jar is full of oxygen. Cover the jar with a greased lid and remove it from the water.

$$\begin{gathered} 2{\mathrm{H}}_2{\mathrm{O}}_2\left(\mathrm{l}\right)\stackrel{{\mathrm{MnO}}_2}{\to }2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right) \\ \mathrm{Hydrogen}\mathrm{peroxide}\mathrm{Water}\mathrm{Oxygen} \end{gathered}$$

• This method of preparation is preferred over other methods because no heating is required and hydrogen peroxide is a safe chemical.
• The rate of evolution of oxygen gas can be controlled by regulating the flow of hydrogen peroxide in the round-bottom flask.