Welcome to
H2O Weekly
Issue
# 002
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Created
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Weekly
Thought
Be not afraid
of growing slowly; be afraid only of standing still.
Weekly Water Events
Chinese Proverb
Weekly Water
Events
1. Forty-one
Anomalies of Water by www.isbu.ac.uk/water (full article)
2. Greenland
glaciers melting at faster pace
3. Global Warming
4. Water Efficiency
5. Water For Life
________________________________________________________
1. Forty-one
Anomalies of Water by www.isbu.ac.uk
Forty-one
Anomalies of Water 1
As water is
so common-place, it is often regarded as a ‘typical’
liquid. In reality water is most atypical as a liquid, with its
properties at low temperatures quite different from its properties
when hot. It has often been stated (e.g. [127]) that life depends
on these anomalous properties of water. In particular, the large
heat capacity, high thermal conductivity and high water content
in organisms contribute to thermal regulation and prevent local
temperature fluctuations, thus allowing us to more easily control
our body temperature. The high latent heat of evaporation gives
resistance to dehydration and considerable evaporative cooling.
Water is an excellent solvent due to its polarity, high dielectric
constant and small size, particularly for polar and ionic compounds
and salts.2 It has unique hydration properties towards biological
macromolecules (particularly proteins and nucleic acids) that
determine their three-dimensional structures, and hence their
functions, in solution. This hydration forms gels that can reversibly
undergo the gel-sol phase transitions that underlie many cellular
mechanisms [351]. Water ionizes and allows easy proton exchange
between molecules, so contributing to the richness of the ionic
interactions in biology.
At 4°C
water expands on heating or cooling. This density maximum together
with the low ice density results in (i) the necessity that all
of a body of fresh water (not just its surface) is close to 4°C
before any freezing can occur, (ii) the freezing of rivers, lakes
and oceans is from the top down, so permitting survival of the
bottom ecology, insulating the water from further freezing, reflecting
back sunlight into space and allowing rapid thawing, and (iii)
density driven thermal convection causing seasonal mixing in deeper
temperate waters carrying life-providing oxygen into the depths.
The large heat capacity of the oceans and seas allows them to
act as heat reservoirs such that sea temperatures vary only a
third as much as land temperatures and so moderate our climate
(e.g. the Gulf stream carries tropical warmth to northwestern
Europe). The compressibility of water reduces the sea level by
about 40 m giving us 5% more land [65]. Water's high surface tension
plus its expansion on freezing encourages the erosion of rocks
to give soil for our agriculture.
Notable amongst
the anomalies of water are the opposite properties of hot and
cold water, with the anomalous behavior more accentuated at low
temperatures where the properties of supercooled water often diverge
from those of hexagonal ice.3 As cold liquid water is heated it
shrinks, it becomes less easy to compress, its refractive index
increases, the speed of sound within it increases, gasses become
less soluble and it is easier to heat and conducts heat better.
In contrast as hot liquid water is heated it expands, it becomes
easier to compress, its refractive index reduces, the speed of
sound within it decreases, gasses become more soluble and it is
harder to heat and a poorer conductor of heat. With increasing
pressure, cold water molecules move faster but hot water molecules
move slower. Hot water freezes faster than cold water and ice
melts when compressed except at high pressures when liquid water
freezes when compressed. No other material is commonly found as
solid, liquid and gas.4
The anomalies
1. Water has
unusually high melting point. [explanation]
2. Water has
unusually high boiling point. [explanation]
3. Water has
unusually high critical point. [explanation]
4. Water has
unusually high surface tension and can bounce. [explanation]
5. Water has
unusually high viscosity. [explanation]
6. Water has
unusually high heat of vaporization. [explanation]
7. Water shrinks
on melting. [explanation]
8. Water has
a high density that increases on heating (up to 3.984°C).
[explanation]
9. The number
of nearest neighbors increases on melting. [explanation]
10. The number
of nearest neighbors increases with temperature. [explanation]
11. Pressure
reduces its melting point (13.35 MPa gives a melting point of
-1°C) [explanation]
12. Pressure
reduces the temperature of maximum density. [explanation]
13. D2O and
T2O differ from H2O in their physical properties much more than
might be expected from their increased mass; e.g. they have increasing
temperatures of maximum density (11.185°C and 13.4°C respectively).
[explanation]
14. Water
shows an unusually large viscosity increase but diffusion decrease
as the temperature is lowered. [explanation]
15. Water's
viscosity decreases with pressure (at temperatures below 33°C).
[explanation]
16. Water
has unusually low compressibility. [explanation]
17. The compressibility
drops as temperature increases down to a minimum at about 46.5°C.
Below this temperature, water is easier to compress as the temperature
is lowered. [explanation]
18. Water
has a low coefficient of expansion (thermal expansivity). [explanation]
19. Water's
thermal expansivity reduces increasingly (becoming negative) at
low temperatures. [explanation]
20. The speed
of sound increases with temperature (up to a maximum at 74°C).
[explanation]
21. Water
has over twice the specific heat capacity of ice or steam. [explanation]
22. The specific
heat capacity (CP and CV) is unusually high. [explanation]
23. Specific
heat capacity; CP has a minimum. [explanation]
24. NMR spin-lattice
relaxation time is very small at low temperatures. [explanation]
25. Solutes
have varying effects on properties such as density and viscosity.
[explanation]
26. None of
its solutions even approach thermodynamic ideality; even D2O in
H2O is not ideal. [explanation]
27. X-ray
diffraction shows an unusually detailed structure. [explanation]
28. Supercooled
water has two phases and a second critical point at about -91°C.
[explanation]
29. Liquid
water may be supercooled, in tiny droplets, down to about -70°C.
It may also be produced from glassy amorphous ice between -123°C
and - 149°C [74] and may coexist with cubic ice up to -63°C
[137]. [explanation]
30. Solid
water exists in a wider variety of stable (and metastable) crystal
and amorphous structures than other materials. [explanation]
31. Hot water
may freeze faster than cold water; the Mpemba effect. [explanation]
32. The refractive
index of water has a maximum value at just below 0°C. [explanation]
33. The solubilities
of non-polar gases in water decrease with temperature to a minimum
and then rise. [explanation]
34. At low
temperatures, the self-diffusion of water increases as the density
and pressure increase. [explanation]
35. The thermal
conductivity of water is high and rises to a maximum at about
130°C. [explanation]
36. Proton
and hydroxide ion mobilities are anomalously fast in an electric
field [explanation]
37. The heat
of fusion of water with temperature exhibits a maximum at -17°C
[15]. [explanation]
38. The dielectric
constant is high and behaves anomalously with temperature. [explanation]
39. Under
high pressure water molecules move further away from each other
with increasing pressure. [explanation]
40. The electrical
conductivity of water rises to a maximum at about 230°C and
then falls. [explanation]
41. Warm water
vibrates longer than cold water. [explanation]
[Anomalies
of water graph]
[Legend]
Some of the
anomalies of water related to temperature.
The graph
uses data that have been scaled between their maximum and minimum
values (see original data).
1 Whether
or not the properties of water are seen to be anomalous depends
upon which materials water is to be compared and the interpretation
of 'anomalous'. For example, it could well be argued that water
possesses exactly those properties that one might deduce from
its structure (see e.g. [402]). Comparisons between water, liquid
sodium, argon and benzene appear to Franks [112] to indicate several
of the properties given above as not being anomalous. However
these materials are perhaps not the most typical of liquids. My
list gives the unusual properties generally understood to make
liquid water (and in one case ice) stand out from 'typical' liquids
(or in one case solids). See [242] for a review concentrating
on the non-anomalous properties of water; i.e. those that are
the 'same' as for other liquids. [Back]
2 It is therefore
difficult to obtain really pure water (e.g. < 5 ppb impurities).
For a review of aqueous solubility prediction see [744]. Note
that ice, in contrast, is a very poor solvent and this may be
made use of when purifying water (e.g. degassing) using successive
freeze-thaw cycles. [Back]
3 Some scientists
attribute the low temperature anomalous nature of water to the
presence of a second critical point; an interesting if somewhat
unproductive hypothesis (as the attribution mixes cause with effect).
Water's anomalies do not require this as an explanation. [Back]
4 The temperature
range of 'hot' and 'cold' water varies in these examples; see
the individual entries for details. [Back]
www.isbu.ac.uk/water/anmlies
2. Greenland
glaciers melting at faster pace
Greenland's
glaciers are melting faster than thought, meaning estimates of
sea-level rise could be too low, scientists warn.
Eric Rignot
of NASA's Jet Propulsion Laboratory in Pasadena, Calif., and Pannir
Kanagaratnam of the University of Kansas included recent changes
in…
http://www.cbc.ca/story/science/national/2006/02/16/glaciers-greenland060216.html
3.Global warming
A hundred
years ago, the phrase "climate change" would not likely
have set anyone's spine tingling, but today it has become fodder
for the latest thrillers and disaster scenarios. The reality is
likely to be less sudden, but possibly no less dramatic.
http://www.cbc.ca/news/background/climatechange/
4. Water Efficiency
Factoid
Did you know
that water-efficient clothes washers use about one-third to one-half
the amount of water of older models? Water-efficient models use
up to about 25 gallons per cycle, while some inefficient models
use over 40 gallons per cycle. The most water-efficient models
can use as little as 12 gallons per cycle.
waternews-join@lists.epa.gov
5.Water For
Life
WATER IS ESSENTIAL
FOR LIFE. Water is crucial for sustainable development, including
the preservation of our natural environment and the alleviation
of poverty and hunger. Water is indispensable for human health
and well-being.
The United
Nations General Assembly, in December 2003, proclaimed the years
2005 to 2015 as the International Decade for Action 'Water for
Life'.
A decade of
action! The primary goal of the 'Water for Life' Decade is to
promote efforts to fulfill international commitments made on water
and water-related issues by 2015.
These commitments
include the Millennium Development Goals to reduce by half the
proportion of people without access to safe drinking water by
2015 and to stop unsustainable exploitation of water resources.
At the World Summit in Johannesburg in 2002, two other goals were
adopted: to aim to develop integrated water resource management
and water efficiency plans by 2005 and to halve, by 2015, the
proportion of people who do not have access to basic sanitation.
http://www.un.org/waterforlifedecade/
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________________________________________________________
Thanks
for reading!
Lorne
Haveruk C.I.D., C.I.C., C.L.I.A
Editors, H20 News
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