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Title: Chemistry/Elements/Hydrogen - Lenntech: Hydrogen Physical data, chemical properties, health and environmental effects.
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Hydrogen (H) - Chemical properties, Health and Environmental effects
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Hydrogen - H
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Chemical properties of hydrogen -
Health effects of hydrogen -
Environmental effects of hydrogen
Atomic number
1
Atomic mass
1.007825
g.mol -1
Electronegativity
according to Pauling
2.1
Density
0.0899*10
-3 g.cm -3 at 20 °C
Melting point
-
259.2 °C
Boiling point
-
252.8 °C
Vanderwaals
radius
0.12
nm
Ionic radius
0.208
(-1) nm
Isotopes
3
Electronic
shell
1s1
Energy of
first ionisation
1311
kJ.mol -1
Discovered by
Henry Cavendish in 1766*
* Hydrogen was observed and collected long before
it was recognized as a unique gas by Robert Boyle
in 1671, who dissolved iron in diluted hydrochloric acid.
source: homepage.mac.com/dtrapp/Elements/properties.html
Hydrogen
First element in the periodic table. In normal conditions it’s
a colourless, odourless and insipid gas, formed by diatomic molecules, H2.
The hydrogen atom, symbol H, is formed by a nucleus with one unit of
positive charge and one electron. Its atomic number is 1 and its atomic
weight 1,00797 g/mol. It’s one of the main compounds of water and of all
organic matter, and it’s widely spread not only in The Earth but also
in the entire Universe. There are three hydrogen isotopes: protium, mass
1, found in more than 99,985% of the natural element; deuterium, mass 2,
found in nature in 0.015% approximately, and tritium, mass 3, which appears
in small quantities in nature, but can be artificially produced by
various nuclear reactions.
Uses: The most important
use of hydrogen is the ammonia synthesis. The use of hydrogen is
extending quickly in fuel refinement, like the breaking down by hydrogen
(hydrocracking), and in sulphur elimination. Huge quantities of hydrogen
are consumed in the catalytic hydrogenation of unsaturated vegetable
oils to obtain solid fat. Hydrogenation is used in the manufacture of
organic chemical products. Huge quantities of hydrogen are used as
rocket fuels, in combination with oxygen or fluor, and as a rocket
propellent propelled by nuclear energy.
Hydrogen can be burned in internal combustion engines. Hydrogen fuel
cells are being looked into as a way to provide power and research is
being conducted on hydrogen as a possible major future fuel. For
instance it can be converted to and from electricity from bio-fuels,
from and into natural gas and diesel fuel, theoretically with no
emissions of either CO2 or toxic chemicals.
Properties: Common hydrogen
has a molecular weight of 2,01594 g. As a gas it has a density of 0.071 g/l
at 0ºC and 1 atm. Its
relative density, compared with that of the air, is 0.0695. Hydrogen is
the most flammable of all the known substances. Hydrogen is slightly
more soluble in organic solvents than in water. Many metals absorb
hydrogen. Hydrogen absorption by steel can result in brittle steel,
which leads to fails in the chemical process equipment.
At normal temperature hydrogen is a not very reactive substance,
unless it has been activated somehow; for instance, by an appropriate
catalyser. At high temperatures it’s highly reactive.
Although
in general it’s diatomic, molecular hydrogen dissociates into free
atoms at high temperatures. Atomic hydrogen is a powerful reductive
agent, even at ambient temperature. It reacts with the oxides and
chlorides of many metals, like silver, copper,
lead, bismuth and mercury, to produce free metals. It reduces some salts to their metallic
state, like nitrates, nitrites and sodium and potassium cyanide. It
reacts with a number of elements, metals and non-metals, to produce
hydrides, like NAH, KH, H2S and PH3. Atomic
hydrogen produces hydrogen peroxide, H2O2,
with oxygen.
Atomic hydrogen reacts with organic compounds to form a complex
mixture of products; with etilene, C2H4, for
instance, the products are ethane, C2H6, and
butane, C4H10. The heat released when the hydrogen
atoms recombine to form the hydrogen molecules is used to obtain high
temperatures in atomic hydrogen welding.
Hydrogen reacts with oxygen to form water and this reaction is
extraordinarily slow at ambient temperature; but if it’s accelerated
by a catalyser, like platinum, or an electric spark, it’s made with
explosive violence.
Health effects of hydrogen
Effects
of exposure to hydrogen: Fire: Extremely flammable. Many reactions may
cause fire or explosion. Explosion: Gas/air mixtures are explosive.
Routes of exposure: The substance can be absorbed into the body
by inhalation. Inhalation: High concentrations of this gas can
cause an oxygen-deficient environment. Individuals breathing such an
atmosphere may experience symptoms which include headaches, ringing in
ears, dizziness, drowsiness, unconsciousness, nausea, vomiting and
depression of all the senses. The skin of a victim may have a blue
color. Under some circumstances, death may occur. Hydrogen is not
expected to cause mutagenicity, embryotoxicity, teratogenicity or
reproductive toxicity. Pre-existing respiratory conditions may be
aggravated by overexposure to hydrogen. Inhalation risk: On loss of containment, a harmful
concentration of this gas in the air will be reached very quickly.
Physical
dangers: The gas mixes well with air, explosive mixtures
are easily formed. The gas is lighter than air.
Chemical dangers: Heating may cause violent combustion or
explosion. Reacts violently with air, oxygen, halogens and strong
oxidants causing fire and explosion hazard. Metal catalysts, such as
platinum and nickel, greatly enhance these reactions.
High
concentrations in the air cause a deficiency of oxygen with the risk of
unconsciousness or death. Check oxygen content before entering area. No
odor warning if toxic concentrations are present. Measure hydrogen
concentrations with suitable gas detector (a normal flammable gas
detector is not suited for the purpose).
First
aid: Fire: Shut off supply; if not possible and no risk to surroundings,
let the fire burn itself out; in other cases extinguish with water
spray, powder, carbon dioxide. Explosion: In case of fire: keep cylinder
cool by spraying with water. Combat fire from a sheltered position.
Inhalation: Fresh air, rest. Artificial respiration may be needed. Refer
for medical attention. Skin: Refer for medical attention.
Environmental effects of hydrogen
Hydrogen in the environment: Hydrogen forms 0.15 % of the
earth's crust, it is the major constituent of water. 0.5 ppm of hydrogen
H2 and varial proportions as water vapour are present in the
atmosphere. Hydrogen is also a majosr component of biomass, consituing
the 14% by weight.
Environmental
stability: hydrogen occurs naturally in the atmosphere. The gas will
be dissipated rapidly in well-ventilated areas.
Effect
on plants or animals: Any effect on animals would be related to oxygen
deficient environments. No adverse effect is anticipated to occur to
plant life, except for frost produced in the presence of rapidly
expanding gases.
Effect
on aquatic life: No evidence is currently available on the effect
of hydrogen on aquatic life.
Back to the
periodic table of elements.
[ Home
] [ Back ] [ More
Information or question on Hydrogen? ]
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