Question

Industrial method of preparation of hydrogen

Answer 1

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 By the electrolysis of water 
   Water is a weak electrolyte .When an electrolyte(acid, base or a salt) is added to water, it conducts    electricity. When electric current is passed, water dissociates into positive and negative ions. Hydrogen    is collected at cathode and oxygen at anode.

   2H2O è 2H2 + O2
    Advantage:
   Hydrogen gas obtained by the electrolysis of water is 100% pure.
   Disadvantage:
   It is an expensive method due to electricity cost.
   By the cracking of methane
   When natural gas is heated in the absence of air up to 700C, it decomposes to produce hydrogen.
   CH4 è C (solid) + 2H2
    Byproduct:
    During cracking of methane "Carbon Black" is obtained as byproduct.
    Uses of Carbon Black : 
                           CITY COLLEGIATE
                   LS- 20, BLOCK # 15, DASTAGIR, KARACHI.

1) In tyre manufacturing industry.
2) Printing ink.
3) Plastic.
4) Paints.
5)Type writer ribbons. 
6)Carbon papers.   By thermal decomposition of ammonia

   When liquid ammonia is vaporized and heated up to 1000C in the presence of a catalyst .It decomposes    to produce nitrogen and hydrogen.
    2NH3 è N2 + 3H2
   Separation of Nitrogen :
    Mixture of N2 and H2 is cooled to -196C .At -196C, N2 liquefies and H2 is separated in gaseous state.
   Steam/ alcohol method
   When methyl alcohol is passed over steam at 250C, a mixture of hydrogen and CO2 is obtained.
     CH3OH + H2O è CO2 + 3H2
    Separation of C02 :-
    When the mixture of H2 and CO2 is introduced in to water at high pressure, CO2 is dissolved in water     and H2 gas is separated.
    Coke and Steam Process
    When steam is passed over red-hot coke, mixture of CO and H2 known as Water Gas is obtained.
     H2O + C è CO + H2
    Separation of CO
    Method No. 1:
    Water gas is cooled to -200C .At -200C temperature CO liquefies and H2 is separated.
   Removal of traces of CO 
   H2 so obtained contains few particles of CO. In order to remove these particles H2 gas is treated with    NaOH.
         CO + NaOH è HCOONa (Sodium formate) 
   Method No. 2
   Water gas is heated with steam in the presence of iron oxide or cobalt oxide. Due to this reaction CO is    converted in to CO2.
         H2 + CO + H2O è CO2 + 2H2 

   Separation of CO2 
   When a mixture of H2 and CO2 is dissolved in water at high pressure, CO2 is dissolved in water and H2    gas is separated. 
   Steam / Natural gas method
         CH4 + H2O è CO + 3H2