Hydrogen
[H2].
Hydrogen, the colourless, odourless gas, is the most common element in the universe. Almost all the material in your body was once Hydrogen, so was once in the centre of a star! However, on Earth, it is only the ninth most common element and exists mainly in combination with other elements in the crust. All these other elements were created in nuclear reactions most probably in our sun. Hydrogen has an atomic number of 1 and its most common isotope, Protium, has a mass number of 1. 99.98% of the Hydrogen in the universe is of this type. Other isotopes of Hydrogen include Deuterium (mass number: 2 due to its extra neutron), which reacts with Oxygen to produce ‘heavy water’, and Tritium (mass number: 3 due to its extra two neutrons), which is radioactive.
Diatomicity
The
Hydrogen atom, first in the periodic table, consists of one proton and one
electron. It is not stable and so does not exist as a single atom. Instead, it
bonds covalently with another hydrogen atom to produce a Hydrogen molecule, H2.
Large amounts of heat are given out in this reaction. Hydrogen exists in
our atmosphere as this diatomic molecule.
CLICK
HERE for diagram
Properties of Hydrogen
Hydrogen
exists as a gas. It is only 1/14 the weight of air – it is the lightest gas
known. For this reason, sound travels much more quickly through it. The higher
frequencies create a higher pitch. This can have amusing effects! Helium, which
you are probably more familiar with, has the same effect. Hydrogen is not
poisonous but cannot sustain life. Because of its lightness, it was previously
used to fill balloons and airships. However, Hydrogen is highly explosive, so
Helium, a noble gas and the second lightest substance known, took its place.
Hydrogen is also very slightly soluble in water. It condenses at a temperature
of 15K (-258°C). In this form, it is used as a rocket fuel. In many of
Hydrogen’s reactions, significant amounts of heat are released. If these
reactions can be controlled, Hydrogen could be a cheap, efficient energy source
in the future (aside from nuclear bombs!).
Reaction of Hydrogen with Oxygen to form Water
Hydrogen
is a component of water. Two Hydrogen atoms covalently bond with an Oxygen atom
to form a Water molecule.
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HERE for diagram
Large
amounts of heat are given off in this reaction also.
Preparation from Water
Scientists
have developed an economical way of producing Hydrogen from Water. Water, being
a simple covalent substance, does not conduct electricity when pure. However,
when acids are dissolved in it, the free moving ions allow a current to be
passed through. This method, electrolysis,
splits/decomposes the Water into Hydrogen and Oxygen. Exactly twice as much
Hydrogen as Oxygen is produced. This is an economical method of producing the
gas.
Test
for Hydrogen
When a gas is produced in a reaction and it is suspected to be Hydrogen, a simple test can be carried out to prove it. Collect some of the gas in a test tube and hold a lighted splint at the end of it. If the gas lights with a pop and a pinkish flame, then it is Hydrogen.
Hydrogen
as a Reducing Agent
CuO
+ H2
=
Cu
+
H2O
Industrial
Preparation from Natural Gas
Natural gas is a Hydrocarbon – a compound of Hydrogen and Carbon. It is drilled for mainly on the ocean bed. In some areas, for example in the North Sea, the Natural Gas is, almost completely, composed of Methane. In some areas, it has other hydrocarbons in it such as Propane and Butane. Methane, CH4, consists of a Carbon atom covalently bonded to four Hydrogen atoms. Propane and Butane are simply more complicated arrays of these two elements.
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Hydrogen can then be, by strong heating, obtained from it. This is the most widely used method in industry.
The Ammonia molecule, NH3 ,consists of three Hydrogen atoms and one Nitrogen atom covalently bonded.
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Almost half of the Hydrogen produced in industry is used to form Ammonia. Aside from water, it is the most important compound of Hydrogen. The Nitrogen and Hydrogen are combined, under high pressure, with the aid of a catalyst. This is a convenient and economical method for the production of Ammonia, although it can also be found naturally. It has a sharp smell and is extremely soluble in water. Ammonia has a range of uses, including conversion to fertilisers, in explosives, in synthetic fibres, in refrigeration and for a variety of other chemical purposes.
e-mail: mairead_mccloskey@talk21.com