COVER STORY
Water drops on glass
INDIAN PLUMBING TODAY
The Miracle
We Call Water!
Asit Adalja
At IPA, our world revolves around water – how to
transport it, filter it, save it, treat it, recycle it, pump it and
control it in various ways. We discuss it at seminars and
conferences. In our hectic ‘modern’ lives we also end up
taking it for granted, but rarely stop to ponder over its
unusual character.
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Water drops on glass
However, chemically speaking, water is really
not common at all. When compared to other
compounds of similar size, composition, and
structure – it is a unique compound! In fact
its properties are so unusual that it would be
irreplaceable.
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Molecular Formula
The molecular formula of water is H2O. In keeping
with the basic rules of chemical nomenclature,
water would have a systematic name of
dihydrogen monoxide, but this is not among the
names published by the International Union of
Pure and Applied Chemistry (IUPAC) and, rather
than being used in a chemical context, the name is
almost exclusively used as a humorous way to refer
to water. IUPAC nomenclature lists ‘Oxidane’ and
‘water’ as the chemical name of H2O.
Theoretically, the other names that can be used
are Hydrogen oxide, Dihydrogen monoxide
(DHMO), Hydrogen monoxide, Dihydrogen
oxide, Hydrogen hydroxide (HH or HOH),
Hydric acid, Hydrohydroxic acid, Hydroxic acid,
Hydrol[1] μ-Oxido dihydrogen.
Dihydrogen
monoxide (DHMO) was once used in a hoax when
a 14 year student in the USA gathered petitions
to ban “DHMO” as a dangerous substance on the
basis of his science project, titled “How Gullible
Are We?”
The Jet d’Eau (Geneva)
A water molecule consists of one atom of oxygen
bound to two atoms of hydrogen. The hydrogen
atoms are “attached” to one side of the oxygen
atom, resulting in a water molecule having a
positive charge on the side where the hydrogen
atoms are and a negative charge on the other
side, where the oxygen atom is. However, the
molecule would not be polar if H2O was linear
like, for example, carbon dioxide, CO2. Each water
molecule is bent so that the positive portions of the
molecule (the hydrogen atoms) are flexed away
from the two filled orbitals of the oxygen.
Blue waters of the Bosphorus
This is the three-dimensional structure of water. The hydrogen
atoms are both on the same side of the molecule, so the charge is
not evenly distributed. (Ben Mills)
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Since opposite electrical charges attract, water
molecules tend to attract each other, making
water kind of “sticky.” All these water molecules
attracting each other mean they tend to clump
together. This is why water drops are, in fact,
drops! If it wasn’t for some of Earth’s forces, such
as gravity, a drop of water would be ball shaped –
a perfect sphere. Even if it doesn’t form a perfect
sphere on Earth, we should be happy, water is
sticky.
Oxygen (O) atom has 2 electrons in the inner orbit
(shell) & 6 electrons in the outer shell. The formula
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for maximum number of electrons in a shell (orbit)
is 2n2. So the innermost shell (1st shell) has 2 x 12 = 2
electrons. The 2nd shell (also outermost shell for O)
can have a maximum of 2 x 22 = 8 electrons. O has
only 6 electrons in the 2nd shell & hence O needs
2 more electrons to have a complete or ‘satisfied’
shell. Hence O combines with 2 atoms of Hydrogen
(H) to get a stable water molecule (H2O).
H has 1 proton (p) and 1 electron (e). A hydrogen
molecule with additional neutron (n) are called
isotopes – Deutrium (1n + 1p) & Tritium (1n +
2p). Combined with Oxygen they form Deutrium
Water molecules ‘sticking’ to each other
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Oxide (D2O) which is used as a moderator for
nuclear reactions.
Boiling Point
The presence of a charge on each of these atoms
(H & O) gives each water molecule a net dipole
moment. Electrical attraction between water
molecules due to this dipole pulls individual
molecules closer together, making it more
difficult to separate the molecules and therefore
raising the boiling point. This attraction is known
as hydrogen bonding.
Water is primarily a liquid under standard
conditions, which is not predicted from its
relationship to other analogous hydrides of the
oxygen family in the periodic table, which are
gases such as hydrogen sulfide (H2S), hydrogen
tellurium (H2Te) or Hydrogen Selenium (H2Se).
The elements surrounding oxygen in the periodic
table, nitrogen, fluorine, phosphorus, sulfur and
chlorine, all combine with hydrogen to produce
gases under standard conditions.
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Let’s compare the boiling of water with some other
chemically similar substances:
Boiling points of various compounds at 1 Atm
Compound Boiling Point - oC
Diethyl Ether
34.6
Acetone
56.2
Methyl Alcohol
64.5
Ethyl Alcohol
78.3
Water
100.0
Mercury
356.6
Water boils at an extremely
high temperature for its
size. The hydrogen bonds
between the molecules
are cohesive forces – they
want to hold the water
molecules together. The
process of boiling requires
that the molecules come
apart: a process that takes
a lot more energy than
expected.
If water behaved like
these other compounds,
it would be liquid
between – 100oC & –
90oC: this means there
would be no water on
earth as temperatures on
earth are always higher
than – 90 oC!
Steam from an electric iron
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Freezing Point
One of the weird things
of water is that ice floats.
The solid state of most
substances is much denser
than the liquid state and
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therefore solids sink. Usually what happens when
a solid is formed is that the molecules become
more tightly packed together. When things melt,
the molecules move apart and get liquid. But
water is different – the solid state is less dense than
the liquid.
Water reaches its maximum density at 4°C
(40°F). Water is different because of hydrogen
bonding.
Ice floats because it is about 9% less dense than
liquid water. In other words, ice takes up about
9% more space than water, so a litre of ice weighs
less than a litre of water. One result of this is
that lakes and rivers freeze from top to bottom,
allowing fish to survive even when the surface of
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a lake has frozen over. If ice sank, the water would
be displaced to the top and exposed to the colder
temperature, forcing rivers and lakes to fill with
ice and freeze solid.
The vibration of molecules increases as temperature
rises and they absorb more energy. For most
substances, this increases the space between
molecules, making warmer liquids less dense
than cooler solids. However, this effect is offset
in water by hydrogen bonding. In liquid water,
hydrogen bonds connect each water molecule to
approximately 3.4 other water molecules. When
water freezes into ice, it crystallizes into a rigid
lattice that increases the space between molecules,
with each molecule hydrogen bonded to 4 other
molecules.
Ice in a glass
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Snow on an Alpine peak
Icicle on a branch
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Phases
Water is unique in that it is the only natural
substance that is found in all three states – liquid,
solid (ice), and gas (steam) – at the temperatures
and pressures normally found on Earth. How does
this temperature – phase relationship affect us? If
water were “normal”, it would be a gas at room
temperature. No lakes, no rain, no body fluids!
And – no life!!!
a lot of dissolved oxygen, while stagnant water
contains little.
Dissolved Oxygen
Although water molecules contain an oxygen
atom, this oxygen is not what is needed by aquatic
organisms living in our natural waters. A small
amount of oxygen, up to about ten molecules of
oxygen per million of water, is actually dissolved
in water. Fish and zooplankton breath this
dissolved oxygen which is needed by them for
survival. Rapidly moving water, such as in a
mountain stream or large river, tends to contain
Specific Gravity
Water has a mass of 1 kg / litre (1 gm / cm) – in
fact, this figure is used as a benchmark to compare
densities of other compounds with water – called
specific gravity.
Universal Solvent
Water is called the “universal solvent” because it
dissolves more substances than any other liquid.
This means that wherever water goes, either
through the ground or through our bodies, it takes
along valuable chemicals, minerals, and nutrients.
Specific Heat
Water has a high specific heat index – 2nd
highest of all known substances (ammonia has
the highest specific heat). This means that water
Pristine lake
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can absorb a lot of heat before it begins to get
hot. This is why water is valuable to industries
and in your car’s radiator as a coolant. The high
specific heat index of water also helps regulate
the rate at which air changes temperature, which
is why the temperature change between seasons
is gradual rather than sudden, especially near
the oceans.
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Specific Heats of a few common substances
Substance
Specific Heat (cal/(gm/oC)
water (liquid)
1.00
water (solid)
0.50
water (gas)
0.47
Water also has a high heat of vaporization
(40.65 kJ/mol). The high specific heat and heat
of vaporization result from the high degree of
hydrogen bonding between water molecules.
One consequence of this is that water is not
subject to rapid temperature fluctuations. On
Earth, this helps to prevent dramatic climate
changes.
Ethyl Alcohol
0.54
Wood
0.42
aluminum
0.21
Glass
0.12
Iron
0.11
If gold, iron and water (all at –273oC – absolute
zero) were to be supplied the same energy, then
gold would melt at 1102oC, iron would have
reached 1299oC and water would have reached
only – 184oC)!
Copper
0.09
silver
0.06
Gold
0.03
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Surface Tension
Water has a very high surface tension. In other
words, water is sticky and elastic, and tends to
clump together in drops rather than spread out
in a thin film. Surface tension is responsible for
capillary action, which allows water (and its
dissolved substances) to move through the roots
of plants and through the tiny blood vessels in
our bodies.
moves from being an arcane science to a voyage
of wonder and pleasure as we learn to relate the
microscopic world of the atom to the greater world
in which we all live. Water certainly is the miracle
we need to understand so that we can learn to
protect this commodity rather than spending
billions of dollars trying to explore its availability
in other parts of the solar system. Let’s learn to
conserve this miracle…
Water in the human body
Living organisms use aqueous solutions e.g.
blood, digestive juices as a medium for carrying
out bio processes. Without water this would not
have been possible.
Note : (1) The above facts have been compiled
from a variety of sources which are listed below:
http://chemistry.about.com/od/waterchemistry
http://imnh.isu.edu/digitalatlas/hydr/basics/
main/chmtxt.htm
http://en.wikipedia.org/wiki/Properties_of_water
http://witcombe.sbc.edu/water/chemistry.html
http://www.biology.arizona.edu/biochemistry/
tutorials/chemistry/page3.html
Encyclopedia Britannica
Colliers Encyclopedia
World Book
Summary
A chemist’s view of the world is not as narrow as
one might think! They start with the atom, and then
go on to the rules governing the kinds of structural
units that can be made from them. They are taught
early on to predict the properties of bulk matter
from these geometric arrangements.
And then we come to H2O, and are shocked to
find that many of these predictions are way off,
and that water (and by implication, life itself)
should not even exist on our planet! But we soon
learn that this tiny combination of three nuclei and
eight electrons possesses special properties that
make it unique among the more than 15 million
chemical species we presently know. When we
stop to ponder the consequences of this, chemistry
Note : (2) All the images carried in this article are
sourced and provided by the author.
Asit Adalja (B.Tech, IITK) is a
consultant with experience in
marketing of plumbing & building
products for the Indian market.
He is also Secretary, IPAMC
and ex Head Marketing of Rajco Metal Industries
(P) Ltd. He can be contacted at [email protected]
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