Describe The Laboratory Preparation Of Hydrogen
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Hey mate.... hydrogen can be obtained in laboratory by the action of dilute sulphuric acid or dilute hydrochloric acid on zinc granules. Take zinc granules in the bottle and fix a two holed cork. Now from one hole fit a thistle funnel. dilute H2 S o4 reacts with zinc to liberate hydrogen gas. This released gas is collected by downward displacement of water water.
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Preparation of Dihydrogen
1) From water : Dihydrogen may be obtained from water by reduction either with active metals or by electricity.
a) By the action of water on active metals
1) Cold Water : Very active metals i.e. alkali and certain alkaline earth metals like Na, K , Ca react with water at room temperature evolving dihydrogen.
2Na + 2H2O ———–> 2NaOH + H2
2K + 2H2O ———–> 2KOH + H2
Ca + 2H2O ———–> 2(Ca)2OH + H2
The reaction with alkali metal is so vigorous and exothermic that the hydrogen involved catches fire. To slow down the reaction, amalgams of these metals are generally used.
In amalgams, only a small surface area of the metal comes in contact with water ,and ,therefore the reaction is slowed down.
2) Boiling water : Less active metals like Zn, Mg , Al decompose boiling water liberating dihydrogen.
Zn + H2O ———–> ZnO + H2
Mg + H2O ———–> MgO + H2
2Al + 3H2O ———–> Al2O3+ H2
3) Steam : Still less active metals like Fe, Sn, Ni decompose steam at high temperature evolving dihydrogen.
3Fe + 4H2O ———–> Fe3O4 + H2
steam magnetic oxide
Temperature: 1023-1073 K
b)By electrolysis of water
Dihydrogen of high purity is usually obtained by the electrolysis of water in the presence of small amount of an acid or a base. During electrolysis, dihydrogen is collected at cathode while dioxygen is liberated at anode.
2H2O (l) ———> 2H2 (g) + O2 (g)
Pure water is only weakly ionized and hence is a poor conductor of electricity but presence of an acid or a base makes it a better conductor of electricity.
This method is not commercially used since it is quite expensive.
2) From alkalis
Metals like Be, Zn, Sn react with boiling alkali solution liberating dihydrogen.
Be + 2NaOH ———–> Na2BeO2 + H2
Zn + 2NaOH ———–> Na2ZnO2 + H2
Sn + 2NaOH + H2O———–> Na2SnO3 + H2
2Al + 2NaOH + 2H2O ———-> 2NaAlO2 + 3H2
3)From acids
Metals which are more electropositive than hydrogen (lie above hydrogen in the electrochemical series) such as Zn, Fe, Mg react with dilute mineral acids to liberate dihydrogen gas.
Zn + H2SO4 ———-> ZnSO4 + H2
Fe +2HCl ———–> FeCl2 + H2
Metals like Copper ,silver ,Mercury which are less electropositive than hydrogen (lie below hydrogen in the electrochemical series) do not liberate hydrogen from acids
1) From water : Dihydrogen may be obtained from water by reduction either with active metals or by electricity.
a) By the action of water on active metals
1) Cold Water : Very active metals i.e. alkali and certain alkaline earth metals like Na, K , Ca react with water at room temperature evolving dihydrogen.
2Na + 2H2O ———–> 2NaOH + H2
2K + 2H2O ———–> 2KOH + H2
Ca + 2H2O ———–> 2(Ca)2OH + H2
The reaction with alkali metal is so vigorous and exothermic that the hydrogen involved catches fire. To slow down the reaction, amalgams of these metals are generally used.
In amalgams, only a small surface area of the metal comes in contact with water ,and ,therefore the reaction is slowed down.
2) Boiling water : Less active metals like Zn, Mg , Al decompose boiling water liberating dihydrogen.
Zn + H2O ———–> ZnO + H2
Mg + H2O ———–> MgO + H2
2Al + 3H2O ———–> Al2O3+ H2
3) Steam : Still less active metals like Fe, Sn, Ni decompose steam at high temperature evolving dihydrogen.
3Fe + 4H2O ———–> Fe3O4 + H2
steam magnetic oxide
Temperature: 1023-1073 K
b)By electrolysis of water
Dihydrogen of high purity is usually obtained by the electrolysis of water in the presence of small amount of an acid or a base. During electrolysis, dihydrogen is collected at cathode while dioxygen is liberated at anode.
2H2O (l) ———> 2H2 (g) + O2 (g)
Pure water is only weakly ionized and hence is a poor conductor of electricity but presence of an acid or a base makes it a better conductor of electricity.
This method is not commercially used since it is quite expensive.
2) From alkalis
Metals like Be, Zn, Sn react with boiling alkali solution liberating dihydrogen.
Be + 2NaOH ———–> Na2BeO2 + H2
Zn + 2NaOH ———–> Na2ZnO2 + H2
Sn + 2NaOH + H2O———–> Na2SnO3 + H2
2Al + 2NaOH + 2H2O ———-> 2NaAlO2 + 3H2
3)From acids
Metals which are more electropositive than hydrogen (lie above hydrogen in the electrochemical series) such as Zn, Fe, Mg react with dilute mineral acids to liberate dihydrogen gas.
Zn + H2SO4 ———-> ZnSO4 + H2
Fe +2HCl ———–> FeCl2 + H2
Metals like Copper ,silver ,Mercury which are less electropositive than hydrogen (lie below hydrogen in the electrochemical series) do not liberate hydrogen from acids
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