Page 169 - Chemistry ICSE Class IX

Study of the First Element : Hydrogen 157
An oxidising agent after oxidising the other substance itself gets
reduced, whereas a reducing agent after reducing the other substance
KVUGNH IGVU QZKFKUGF
The reactions involving simultaneous oxidation and reduction are
called oxidation-reduction or TGFQZ TGCEVKQPU
The following table summarises the various terms used in oxidation
and reduction:
Terms Electron change Oxidation number change
Oxidation Loss of electrons Increases
Reduction Gain of electrons Decreases
Oxidising agent Gains electrons Decreases
Reducing agent Loses electrons Increases
Substance oxidised Loses electrons Increases
Substance reduced Gains electrons Decreases

Physical and Chemical Properties of Hydrogen

What are the physical properties of hydrogen
Some characteristic properties of hydrogen are described below:
ƒ %QNQWT QFQWT VCUVG Hydrogen is a colourless, odourless and tasteless >ŝƋƵŝĚ ŚLJĚƌŽŐĞŶ ŝƐ Ă ĐŽůŽƵƌůĞƐƐ ůŝƋƵŝĚ͘
gas. ŽŝůŝŶŐ ƉŽŝŶƚ ͗ ʹϮϱϯΣ
ƒ &GPUKV[ Hydrogen is the lightest element known. The density of &ƌĞĞnjŝŶŐ ƉŽŝŶƚ ͗ ʹϮϱϵΣ
hydrogen gas is 0.09 g/L.
ƒ 5QNWDKNKV[ Hydrogen is slightly soluble in water – 21.5 mL per litre of
water at NTP.
ƒ 6JGTOCN EQPFWEVKXKV[ Hydrogen is the best gaseous conductor of
heat. It conducts heat ve times better than air.
ƒ 1EENWUKQP Hydrogen is adsorbed/absorbed by metals like platinum,
palladium in large quantities. Palladium can hold 800 times its volume
of hydrogen. Such hydrogen can be recovered by heating palladium
in vacuum. This process is known as occlusion.

What are the chemical properties of hydrogen
ƒ 4GCEVKXKV[ Hydrogen is quite reactive. It can form compounds by
losing or by sharing its only electron in the rst (K) shell.
Hydrogen also reacts by gaining one electron from highly
electropositive metals.
ƒ #EVKQP QP NKVOWU Hydrogen has no effect on litmus because it is
neutral. Some typical chemical reactions of hydrogen are described
below.

Reactions of hydrogen with nonmetals
ƒ 9KVJ QZ[IGP QT CKT Hydrogen burns in air (or oxygen) with a
nonluminous (blue) ame. The reaction is highly exothermic and
vigorous. dŚĞ ƌĞĂĐƟǀŝƚLJ ŽĨ ŚLJĚƌŽŐĞŶ ǁŝƚŚ
2H (g) + O (g) o 2H O(g) + Heat ŚĂůŽŐĞŶƐ ĨŽůůŽǁƐ ƚŚĞ ŽƌĚĞƌ͗
2
2
2
F х ů х ƌ х / ͘
Hydrogen-air mixture burns explosively. Ϯ Ϯ Ϯ Ϯ
ƒ 9KVJ JCNQIGPU Hydrogen also combines explosively with uorine
and chlorine, and less readily with bromine and iodine to produce