Question

(a) Starting from hydrogen peroxide how is oxygen gas prepared in laboratory?
(b) What is the function of manganese dioxide?
(c) Write fully balanced equation for the liberation of oxygen from hydrogen peroxide.
(d) Why is the above method preferred to any other method?

Answer 1

(a) When 20% hydrogen peroxide is poured in funnel and allowed to drip into the flask containing 5g of manganese dioxide, oxygen gas is evolved which is apparent from the bubbles coming out of the water trough. Allow the first few bubbles to escape, as they contain air. Place a glass cylinder filled with water in inverted position over the beehive shelf. The oxygen will collect in the cylinder by the downward displacement of water.

(b) Manganese dioxide does not take part in the chemical reaction. However, it accelerates the rate of decomposition of hydrogen peroxide acting as a catalyst.

(c)  

\[\ce{\underset{\text{Hydrogen peroxide}}{2H2O2}->[MnO2][Catalyst]\underset{\text{Water}}{2H2O} + \underset{\text{Oxygen}}{O2}}\]

(d) This method is preferred to any other method to prepare oxygen because :

• The oxygen gas is evolved at room temperature. No heating is required.
• The rate of evolution of oxygen is fairly fast.
• Hydrogen peroxide or manganese dioxide are not dangerous chemicals and hence, can be handled easily.