Page 155 - ICSE Chemistry 8

A few zinc granules are placed in a fl at-bo om fl ask and the mouth of the fl ask is closed with a two-holed
rubber stopper. A thistle funnel is passed through one hole and a delivery tube is introduced through the
other hole. The other end of the delivery tube is placed inside a beehive shelf kept in a trough containing
water. A gas jar is inverted over the beehive shelf.
Dilute sulphuric acid (H SO ) is poured through the thistle funnel into the fl ask un l all the granules are
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4
completely covered with the acid. A vigorous reac on takes place and hydrogen bubbles rise up from the
surface of the zinc granules. The fi rst few bubbles of gas are allowed to escape. The bubbles of hydrogen
gas are transferred through the delivery tube and collected in the gas jar by the downward displacement
of water. In this method, hydrogen displaces water and gets collected in the gas jar.

hydrogen gas

dilute hydrochloric acid
water
beehive shelf
zinc granules

Fig. 7.3: Laboratory preparation of hydrogen
Safety Precautions
• The apparatus must be air ght so that any leakage of gas does not take place. This is necessary as
hydrogen forms an explosive mixture with air.

• No fl ame should be brought near the apparatus because if the gas leaks, it will be infl ammable.
• The lower end of the thistle funnel should be completely covered with dilute acid.
• The fi rst few bubbles from the delivery tube should not be collected as they contain air.

Bosch’s Process: Industrial Production of Hydrogen

Bosch’s process is used to produce hydrogen on a large scale. There are three main steps involved in the
Bosch’s process.
Step 1: ProducƟ on of Water Gas

Water gas is a mixture of carbon monoxide and hydrogen. It is formed when water in the form of
superheated steam is passed over carbon (white-hot coke) at a temperature of about 1000°C.
o
1000 C
C(s) + H O(l) CO(g) + H (g) + Heat
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2
Coke Water Water gas
Step 2: Conversion of Carbon Monoxide to Carbon Dioxide
It is diffi cult to separate the mixture of hydrogen and carbon monoxide. Therefore, we convert CO to
CO and in order to do so, the mixture is made to react with equal volume of steam in the presence of
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iron chromate which acts as a catalyst and chromic oxide as the promotor. Carbon monoxide oxidises to
carbon dioxide.

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