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

(b) What is the role of manganese dioxide in the preparation of oxygen?

(c) Write the balanced chemical equation for the above chemical reaction.

(d) Why is hydrogen peroxide preferred in the preparation of oxygen gas?

(e) Why is oxygen collected by downward displacement of water?

(f) What happens when a glowing splinter is introduced in a jar containing oxygen?

(g) What happens when oxygen gas is passed through alkaline pyrogallol solution?

(a) Oxygen is prepared from hydrogen peroxide in the laboratory by the following ways-

1. A small quantity of manganese dioxide is taken in a flat bottom flask.
2. Hydrogen peroxide is added drop by drop into the flask by help of thistle funnel as shown in the below figure.

3. Manganese dioxide decomposes hydrogen peroxide very fast and liberates oxygen which passes through the delivery tube and bubbles out through the water in the trough.
4. A gas jar filled with water is inverted over beehive shelf. Oxygen is collected in the jar by downward displacement of water.

(b) Manganese dioxide acts as a catalyst, it decomposes hydrogen peroxide very fast and liberates oxygen.

(c) 2H₂O₂ $\xrightarrow[\text{as catalyst}]{\text{MnO}_2}$ 2H₂O + O₂ [g]

(d) Hydrogen peroxide is preferred in the preparation of oxygen gas because:

1. No heating is required.
2. The rate of evolution of oxygen is moderate and therefore under control.
3. Hydrogen peroxide is a safe chemical.

(e) Oxygen is collected by downward displacement of water because:

1. Oxygen is slightly heavier than air, so it cannot be collected over air.
2. Oxygen is only slightly soluble in water i.e. 0.7% only. So it can be collected over water without fear of excessive dissolution.

(f) When a glowing splinter is introduced in a jar containing oxygen, the glowing splinter rekindles, but the gas does not catch fire.

(g) When oxygen gas is passed through alkaline pyrogallol solution, it turns brown.