Page 171 - Chemistry ICSE Class IX

Study of the First Element : Hydrogen 159

Reducing character of hydrogen - Reaction with metal oxides
Hydrogen is a good reducing agent. Hydrogen reduces many metal salts,
e.g., halides and oxides, to the corresponding metals. This reducing property
of hydrogen is used in obtaining certain metals from their oxides where
carbon cannot be used for reduction purposes.
HgO(s) + H (g) o Hg(l) + H O(l)
2
2
mercury(II) oxide hydrogen mercury water
CuO(s) + H (g) o Cu(s) + H O(l)
2
2
copper(II) oxide copper
Cu O(s) + H (g) o 2Cu(s) + H O(l)
2
2
2
copper(I) oxide copper
Ag O(s) + H (g) o 2Ag(s) + H O(l)
2
2
2
silver oxide silver
Fe O (s) + 4H (g) o 3Fe(s) + 4H O(l)
3
4
2
2
ferrosoferric oxide iron
Tungsten (W) and molybdenum (Mo) are extracted from their oxides
by hydrogen reduction process. Hydrogen cannot reduce heated Al O .
3
2
WO (s) + 3H (g) o W(s) + 3H O(l)
2
3
2
tungsten oxide tungsten
MoO (s) + 3H (g) o Mo(s) + 3H O(l)
3
2
2
molybdenum oxide molybdenum
Hydrogenation reaction ŽĂů ĐĂŶ ďĞ ŚLJĚƌŽŐĞŶĂƚĞĚ ƚŽ
Unsaturated organic compounds combine directly with hydrogen to ƉƌŽĚƵĐĞ Ă ŵŝdžƚƵƌĞ ŽĨ ůŝƋƵŝĚ
produce saturated compounds. Such a reaction is known as hydrogenation. ŚLJĚƌŽĐĂƌďŽŶƐ ǁŚŝĐŚ ŝƐ ĚŝƐƟůůĞĚ ƚŽ
This is illustrated by the reaction of ethylene (ethene) and H to form ethane, ŽďƚĂŝŶ syntheƟc petroleum͘
2
C H .
2
6
Ni
H C = CH (g) + H (g) o H C – CH (g)
2
3
3
2
2
ethene 250°C ethane
Unsaturated oils are hydrogenated on commercial scale for converting
liquid fats, such as vegetable oils, into solid fats (vegetable ghee).
Finely divided Ni
Oils(l) + H (g) o Vegetable ghee
2
250°C
Uses of Hydrogen
What are the uses of hydrogen
Hydrogen is a very valuable element from commercial point of view. Some ,LJĚƌŽŐĞŶ ŚĂƐ ƚŚĞ ŚŝŐŚĞƐƚ ĐĂůŽƌŝĮĐ
of its major industrial uses are as follows: ǀĂůƵĞ͘
ƒ (QT OCPWHCEVWTKPI KPFWUVTKCN EQORQWPFU It is used for the
manufacture of ammonia (Haber’s process), hydrochloric acid,
methanol, etc.
ƒ +P J[FTQIGPCVKQP TGCEVKQPU It is used for the hydrogenation of oils,
i.e., for the manufacture of vegetable ghee.
ƒ +P OGVGQTQNQIKECN DCNNQQPU It is used in lling balloons and airships.
Because of its combustible nature and high diffusion rate, generally DĂŶLJ ŵŽƚŽƌ ĐŽŵƉĂŶŝĞƐ͕ ŝŶĐůƵĚŝŶŐ
a mixture of 85% helium and 15% hydrogen is used for this purpose. ĂŝŵůĞƌͲ ŚƌLJƐůĞƌ ĂŶĚ &ŽƌĚ͕ ŚĂǀĞ
Nowadays, however, only hot air balloons are used. ĂůƌĞĂĚLJ ƉƌŽĚƵĐĞĚ ƉƌŽƚŽƚLJƉĞƐ ŽĨ
ƒ +P QZ[ J[FTQIGP VQTEJ It is used for producing oxy-hydrogen ame hydrogen-powered ǀĞŚŝĐůĞƐ ƌƵŶ ŽŶ
to be used for welding purposes due to its high temperature (3000°C). ĨƵĞů ĐĞůůƐ͘