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Types of Hydrogen

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1.    Molecular Hydrogen (H2)

↪ Molecular hydrogen is formed by the combination of two hydrogen atoms bonded together through a covalent bond (H-H). It is also called dihydrogen.

↪ Molecular hydrogen is formed when reactive metals displace hydrogen from dilute mineral adds and exists as gas at room temperature.

2.    Atomic Hydrogen [H]

 

↪ An atomic hydrogen is one which contains one proton at its nucleus and one and one electron in its K - shell. Due to this reason, it has strong desire to combine with another hydrogen by the sharing of electron resulting the formation of molecular hydrogen.
             

 Preparation of atomic hydrogen
   

↪ Atomic hydrogen is prepared by passing a stream of hydrogen gas at atmospheric pressure through an electric arc struck between tungsten electrodes at about 2000-3OOO°C.



↪ Heat is produced when some of the hydrogen burns with oxygen.
↪ Atomic hydrogen is strong reducing agent. It is more powerful reducing agent that molecular and nascent hydrogen.

{Notes: LEO = Loss of electron is Oxidation and GER = Gain of electron is Reduction}



i. It reduces oxygen and carbon monoxide


ii. It reduces ethene to ethane.

iii. It reduces aqueous solution of H2O2, AgNON­3, copper acetate.

iv. Metallic oxides and chlorides are reduced.


Uses: Atomic hydrogen is used as reducing agent and in welding the metals

3.    Nascent Hydrogen

↪ The term nascent is derived from the Latin word Nascor meaning newly born.

↪ So, a nascent hydrogen which is just formed by means of a chemical reaction. It is also regarded as the hydrogen formed in contact to the to be reduced.

↪ It is very short-lived species and it quickly reacts with each other to form molecular hydrogen.

↪ Nascent hydrogen is more powerful reducing agent than molecular hydrogen which can be proved by the following chemical reactions.

i. Reaction with acidified KMnO4  

↪ When molecular hydrogen obtained by reacting zinc with dil. Sulphuric acid is passed through acidified solution of KMnO4 then pink color of KMnO4 remain unchanged.

↪ But Nascent hydrogen obtained by dropping a piece of zinc into acidified KMnO4 discharge pink color of KMnO4 due to the reduction caused by nascent hydrogen.

ii.  Reaction with acidified K2Cr2O7
↪ Molecular hydrogen can’t change the orange color of acidified K2Cr2O7.

↪ But nascent hydrogen obtained by dropping a piece of zinc into acidified K2Cr2O7 turns the orange color of acidified K2Cr2O7 into green due to reduction caused by nascent hydrogen.

iii. Reaction with acidified FeCl3

↪ When molecular hydrogen is passed through acidified solution of ferric chloride then yellow color of FeCl3 remained unchanged.

↪ But when a piece of Zn is dropped into acidified solution of FeClthen yellow color of FeCl3 turns green due to reduction of FeClinto FeCl2.

 Relative Reactivity of Nascent Hydrogen

‏‏Nascent hydrogen is more powerful reducing agent over molecular hydrogen due to following reasons.

↪ Nascent hydrogen is more energetic as it is associated with the excess energy that is released during the formation of molecular hydrogen.

↪ As nascent hydrogen is just formed by means of chemical reaction it has high internal pressure so more reactive than molecular hydrogen.

⁕ Differences between Nascent and Atomic Hydrogen

Nascent Hydrogen

Atomic Hydrogen

1. It is prepared at ordinary temperature by the reaction of metals with acid, alkali and water.

1. It is prepared at high temperature of about 3000℃ by dissociating H2 molecule.

2. It is weaker reducing agent than atomic hydrogen.

2. It is stronger reducing agent than nascent hydrogen.

3. It can never be isolated.

3. Atomic hydrogen can be isolated.

4. It can't reduce metallic salts and oxides.

4. It can reduce certain metallic salts like AgCl, Cuo, CdS.
AgCl + H ↣ Ag + HCl