In water, organic compounds, etc.
- Action of active metals on water.
2Na + 2H2O → 2NaOH + H2↑
2K + 2H2O → 2KOH + H2↑
Ca + 2H2O → Ca(OH)2 + H2↑
- Action of less active metals on steam –
Zn + H2O → ZnO + H2↑
Mg + H2O → MgO + H2↑
Over red hot iron, steam forms hydrogen
3Fe + 4 H2O → Fe3O4 + 4H2↑
- From acids
Zn + H2SO4 → ZnSO4 + H2↑
Zn + 2HCl → ZnCl2 + H2↑
The intensity with which metals displace hydrogen from acids depends on a series
K, Ca, Na,
Mg, Al, Zn, Fe,
Ni, Sn, Pb,
Cu, Hg, Ag, Au, Pt
Do not displace
- From alkalies
Zn + 2NaOH → Na2ZnO2 + H2↑
Zn + 2KOH → K2ZnO2 + H2↑
2Al + 2NaOH + 2H2O → 2NaAlO2 + 3H2↑
2Al + 2KOH + 2H2O → 2KAlO2 + 3H2↑
The gas is dried by CaCl2
- Steam is passed over heated coke to produce water gas.
C + H2O → CO + H2↑
Water gas and excess steam are passed over a catalyst, iron (III) oxide.
CO + H2 + H2O → CO2 + 2H2↑
Carbon dioxide is absorbed by caustic soda or potash to obtain hydrogen.
- If water is electrolyzed, hydrogen can be collected at the cathode.
- It is a colorless, odorless gas.
- It is 0.069 times as heavy as air.
- It is almost insoluble in water.
- B.P = -253°C, M.P. = -259.4°C.
- Noble metals readily absorb hydrogen when finely divided.
- It is combustible, but does not support combustion.
2H2 + O2 → 2H2O
- Hydrogen and chlorine react explosively in direct sunlight.
H2 + Cl2 → 2HCl
- If hydrogen is passed through boiling sulfur, it forms hydrogen sulfide
H2 + S → H2S
- Combines with nitrogen in the presence of catalysts to form ammonia.
N2 + 3H2 → 2NH3
- It reduces metal oxides
H2 + CuO → H2O + Cu
H2 + PbO → H2O + Pb
Fe2O3+ 3H2 → 3H2O + 2Fe
- As a fuel – in rockets, in torches. In electric arcs, it absorbs energy to split to atoms, and outside the arc it forms molecules releasing energy.
- In self-lighting jets – hydrogen is absorbed by finely divided metals, and heat is released, which is used to ignite fuel.
- In meteorological balloons.
- In the presence of catalysts, it is used to make petrol from coal.
- In the extraction of metals
WO3 + 3H2 → W + 3H2O
- Hydrogenation of oils – If heated with oils to 150° - 200°C at 5 atmos. pressure in the presence of nickel, oils are hydrogenated to a semi-solid state.
- To make ammonia and hydrochloric acid by the direct combination of elements.