Question

(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 ?

Answer 1

(a) Take manganese dioxide in a round bottom flask and add hydrogen peroxide drop by drop to it, which acts; a catalyst as shown in the figure. Collect oxygen by downward displacement of water.

(b) Manganese dioxides act as a catalyst.

(c)

(d) H ₂O₂ is preferred for lab preparation of oxygen because of following reasons.

1. No heating is required.

2. The rate of evolution of oxygen (O₂) is moderate and under control. H₂O₂ is a safe chemical.

(e) Since the water is displaced downward by the gas collecting in the jar, the process is called downward displacement of water. 

The reasons are :

1. Oxygen is only slightly soluble in water. Therefore it can be collected over water without fear of excessive dilution.

2. Oxygen is slightly heavier than air, so it cannot collected over air.

(f) Introduction of glowing splinter in the jar. The glowing splinter rekindles, but the gas does not catch fire.

(g) Alkaline pyrogallol solution turns brown when oxygen is passed through it.