Hydrogen

 

Hydrogen

Chemical formula	H
Atomic Number	1
OTP appearance	colorless gas
Molar Mass(g/mol)	1
Density(g/cc)	0.00009
Melting Point(°C)	-260
Boiling Point(°C)	-253
Fuel Value(MJ/kg)	120.21
Speed of sound 20°C, 1atm (m/s)	1270
NFPA 704	4 0 0

Uses

Justification Questioned

Secondary

• As a fuel
• As a lifting gas

Natural Sources

• Elemental hydrogen does occur naturally in the ionosphere, but is not accessible in general
• Hydrogen occurs naturally in water and virtually all acids

Hazards

The bond energy released when hydrogen is produced is often sufficient to ignite it if it comes into contact with oxygen. Be careful.

Production

Elemental Hydrogen

Berthelot

In an oxygen-free environment, forcing water or steam into a red-hot iron tube results in hydrogen gas exiting the system:

3 Fe + 4 H₂O → Fe₃O₄ + 4 H₂

Electrolysis

2 H₂O → 2 H₂ + O₂ ; Catalyzed by various salts including (Co,Fe)P₄N₂

Metal reactivity series

acid

• from any acid (sulfuric acid) and zinc powder:

  Zn + H₂SO₄ + 7 H₂O → ZnSO₄(H₂O)₇ + H₂

• or even acetic acid and smithsonite

  CH₃COOH + ZnCO₃ → Zn(CH₃COO)₂ + H₂(g)

• from the metals nickel, tin and lead (as well as Cd and Co) and mineral acids (sulfuric, hydrochloric and nitric for instance)

  Sn(s) + H₂SO₄(l) → SnSO₄(s) + H₂(g)

alkali

• Aqueous sodium hydroxide and aluminum react to produce hydrogen gas. This should be done in an oxygen free environment to prevent the heat of the reaction from igniting the hydrogen.

  2 Al + 2 NaOH + 2 H₂O → 2 NaAlO₂ + 3 H

water

• from water and potassium, sodium, barium and calcium (as well as Li, Cs, Rb and Sr)

  2 Na(s) + 2 H₂O(l) → 2 NaOH(aq) + H₂(g)

  Ca(s) + 2 H₂O(l) → Ca(OH)₂(aq) + H₂(g)

• from steam and (clean, unoxidized, metallic) magnesium, aluminum, manganese, zinc, chromium and iron (as well as Ti)

  4 Al(s) + 6 H₂O(v) → 2 Al₂O₃(s) + 3 H₂(g)