Page 166 - Chemistry ICSE Class IX

154 ICSE Chemistry – 9
heat
Fe O (s) + 2CO(g) + 2H (g) o 3Fe(s) + 2CO (g) + 2H O(g)
,ŝŐŚ ŵŽůĞĐƵůĂƌ ŵĂƐƐ ŚLJĚƌŽĐĂƌďŽŶƐ 3 4 2 2 2
ŽďƚĂŝŶĞĚ ĨƌŽŵ Žŝů ƌĞĮŶĞƌŝĞƐ͕ ƐƵĐŚ water gas
ĂƐ ŶĂƉŚƚŚĂ ĂŶĚ ĨƵĞů Žŝů͕ ĂƌĞ ĐƌĂĐŬĞĚ In actual practice, steam is passed over hot iron for 10 minutes (gassing
ƚŽ ƉƌŽĚƵĐĞ ůŽǁ ŵŽůĞĐƵůĂƌ ŵĂƐƐ
ŚLJĚƌŽĐĂƌďŽŶƐ ĂŶĚ ŚLJĚƌŽŐĞŶ ĐĂŶ ďĞ period) and water gas is blown over heated oxide for 20 minutes (reduction
ŽďƚĂŝŶĞĚ ĂƐ Ă ďLJͲƉƌŽĚƵĐƚ͘ period). In order to make the process continuous, both the reactions are
carried out alternately.
ͻ
sĞƌLJ ƌĞĐĞŶƚůLJ͕ ƐĐŝĞŶƟƐƚƐ Ăƚ ƚŚĞ From hydrocarbons
hŶŝǀĞƌƐŝƚLJ ŽĨ tŝƐĐŽŶƐŝŶ͕ h^ ͕ ŚĂǀĞ
ĚĞǀĞůŽƉĞĚ Ă ŵĞƚŚŽĚ ƚŽ ƉƌŽĚƵĐĞ Hydrogen can also be obtained on commercial scale from lower
ŚLJĚƌŽŐĞŶ ĨƌŽŵ glucose soluƟon͘ hydrocarbons, such as methane, natural gas (it contains methane as the
'ůƵĐŽƐĞ ďĞŝŶŐ Ă ƉůĂŶƚ ƉƌŽĚƵĐƚ͕ major component) and from methanol by steam reformer process (or
ƚŚŝƐ ŵĞƚŚŽĚ ƉƌŽǀŝĚĞƐ Ă ǁĂLJ ƚŽ steam reforming).
ŽďƚĂŝŶ ĐŚĞĂƉĞƌ ŚLJĚƌŽŐĞŶ ƚŚƌŽƵŐŚ Ă Lower hydrocarbons, such as methane (CH ), when mixed with
renewable natural cycle͘ 4
steam and passed over a nickel catalyst at 800-900°C, produce a mixture
containing CO, CO and H .
2
2
nickel catalyst
CH (g) + H O(g) o CO(g) + 3H (g)
2
2
4
800-900°C, 30 atm.
methane steam
nickel catalyst
CH (g) + 2H O(g) o CO (g) + 4H (g)
4
2
2
2
800-900°C, 30 atm.
methane steam
The mixture containing CO(g), CO (g) and H (g) is mixed with more
2
2
steam, cooled to 400°C and passed over an iron-copper catalyst. Here,
CO(g) gets oxidised to CO (g).
2
iron-copper catalyst
CO(g) + H O(g) o CO (g) + H (g)
2
2
2
steam 400°C
The CO gas present in the mixture is removed by absorbing in a
2
solution of potassium carbonate (K CO ) or ethanolamine. Potassium
3
2
carbonate and ethanolamine are regenerated by heating.
Oxidation
What is oxidation
Any process which involves, (i) the addition of oxygen or any other
electronegative radical or (ii) the removal of hydrogen or any other
electropositive radical, is termed oxidation. The following examples will
make it clear:
(i) Addition of oxygen:
C + O o CO 2
2
2Mg + O o 2MgO
2
4P + 5O o 2P O 5
2
2
Here carbon, magnesium and phosphorus gain oxygen and are
oxidised to their respective oxides.
(ii) Addition of an electronegative radical:
2FeCl 2 + Cl o 2FeCl 3
2
4FeSO + 2H SO + O o 2Fe (SO ) + 2H O
2
4
4 3
2
2
2
4
2SnCl + 4HCl + O o 2SnCl 4 + 2H O
2
2
2
In these examples, ferrous chloride, ferrous sulphate and stannous
chloride have gained chloride, sulphate and chloride radicals (or ions),
respectively and have been thus oxidised.