Page 174 - Chemistry ICSE Class IX

162 ICSE Chemistry – 9

Let us say it Again

— Occurrence. Hydrogen occurs on the Sun and other stars. On the earth, it mostly occurs in the combined state — as
water, snow, hydrocarbons and carbohydrates, etc.
— Preparation. Hydrogen can be obtained from water, (a) by the action of active metals, (b) by electrolysis.
 Hydrogen can be prepared by the action of metals, such as zinc and magnesium, on dilute acids. This method is
commonly used for laboratory preparation of hydrogen.
 Hydrogen can also be prepared by the action of metals, such as zinc, aluminium and tin, on boiling alkalis, such as
sodium hydroxide.
— Density. Hydrogen is the lightest gas known.
— Nature. Hydrogen gas is highly inflammable. It burns in the air explosively producing water.
— Formation of hydrides. Hydrogen reacts with some metals and nonmetals producing hydrides.
— Reducing nature. Hydrogen is a strong reducing agent.
— Uses of hydrogen. Hydrogen is used for the manufacture of ammonia, hydrochloric acid, vegetable ghee, methanol, etc.
It is used for filling air balloons and airships. It is also used as a fuel in rockets.
— Hydrogenation. Addition of hydrogen to unsaturated organic compounds to produce saturated compounds is termed
as hydrogenation.