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Water (H
Ball-and-stick model of a water molecule
Space filling model of a water molecule
IUPAC name
water, oxidane
Other names
Hydrogen hydroxide (HH or HOH), hydrogen oxide, dihydrogen monoxide (DHMO) (systematic name[1]), hydrogen monoxide, dihydrogen oxide, hydric acid, hydrohydroxic acid, hydroxic acid, hydrol,[2] μ-oxido dihydrogen, κ1-hydroxyl hydrogen(0)
3D model (JSmol)
Beilstein Reference 3587155
ECHA InfoCard 100.028.902
Gmelin Reference 117
PubChem {{{value}}}
RTECS number ZC0110000
SMILES {{{value}}}
Molar mass 18.01528(33) g/mol
Appearance White crystal-like solid, almost colorless liquid with a hint of blue, colorless gas
Odor None
Density Liquid:[3]
0.9998396 g/mL at 0 °C
0.9970474 g/mL at 25 °C
0.961893 g/mL at 95 °C
0.9167 g/ml at 0 °C
Melting point 0.00 °C (32.00 °F; 273.15 K) [a]
Boiling point 99.98 °C (211.96 °F; 373.13 K) [5][a]
Solubility Poorly soluble in haloalkanes, aliphatic and aromatic hydrocarbons, ethers.[6] Improved solubility in carboxylates, alcohols, ketones, amines. Miscible with methanol, ethanol, propanol, isopropanol, acetone, glycerol, 1,4-dioxane, tetrahydrofuran, sulfolane, acetaldehyde, dimethylformamide, dimethoxyethane, dimethyl sulfoxide, acetonitrile. Partially miscible with Diethyl ether, Methyl Ethyl Ketone, Dichloromethane, Ethyl Acetate, Bromine.
Vapor pressure 3.1690 kilopascals or 0.031276 atm[7]
Acidity (pKa) 13.995[8][9][b]
Basicity (pKb) 13.995
Conjugate acid Hydronium
Conjugate base Hydroxide
Thermal conductivity 0.6065 W/(m·K)[12]
1.3330 (20 °C)[13]
Viscosity 0.890 cP[14]
1.8546 D[15]
Std enthalpy of
−285.83 ± 0.04 kJ/mol[6][16]
Standard molar
69.95 ± 0.03 J/(mol·K)[16]
Specific heat capacity, C 75.385 ± 0.05 J/(mol·K)[16]
Main hazards Drowning
Avalanche (as snow)

Water intoxication
(see also Dihydrogen monoxide parody)

NFPA 704

NFPA 704.svg

Flash point Non-flammable
Related compounds
Other cations Hydrogen sulfide
Hydrogen selenide
Hydrogen telluride
Hydrogen polonide
Hydrogen peroxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☑Y verify (what is ☑Y☒N ?)
Infobox references
Water in three states: liquid (including the clouds, which are aerosols), solid (ice) and gas (water vapour, which is invisible)

Water (H
) is a transparent, tasteless, odorless, and almost colorless chemical substance and covers over 70% of Earth's surface. No known life can live without it.

Lakes, oceans, seas, and rivers are made of water. Precipitation is water that falls from clouds in the sky. It may be rain (liquid) if it is warm, or it may be frozen if it is cold. If water gets very cold (below 0 °C (32 °F)), it freezes and becomes ice, the frozen variant of water. If water gets very hot (above 100 °C (212 °F)), it boils and becomes steam or water vapor.

Water has been present on Earth since its earlier days and is constantly moved around it by the water cycle.[17] Water is very important for life, probably essential.[18] However, some studies suggest that by 2025 more than half the people around the world will not have enough fresh water.[19]

Physical chemistry of water[change | change source]

Water is a fluid. Water is the only chemical substance on Earth that exists naturally in three states. People know of over 40 anomalies about water.[20][21] Unlike most other liquids such as alcohol or oil, when water freezes, it expands by about 9%.[22][23][24] This expansion can cause pipes to break if the water inside them freezes.

Water is a molecule made of 2 hydrogen atoms and 1 oxygen atom. Its chemical formula is H2O. Like other liquids, water has a surface tension, so a little water can make drops on a surface, rather than always spreading out to wet the surface.[25] Things having something to do with water may have "hydro" or "aqua" in their name, such as hydropower or aquarium, from the Greek and Latin names for water. It is also called the universal solvent, because it dissolves many things.

In small amounts, water appears to have no colour but in large amounts (such as seas or lakes), it has a very light blue color.

Uses of water[change | change source]

Plants and animals (including people) are mostly water inside, and must drink water to live. It gives a medium for chemical reactions to take place, and is the main part of blood. It keeps the body temperature the same by sweating from the skin. Water helps blood carry nutrients from the stomach to all parts of the body to keep the body alive. Water also helps the blood carry oxygen from the lungs to the body. Saliva, which helps animals and people digest food, is mostly water. Water helps make urine. Urine helps remove bad chemicals from the body. The human body is between 60% and 70% water, but this value differs with age; i.e. a foetus is 95% water inside.

Water is the main component of drinks like milk, juice, and wine. Each type of drink also has other things that add flavor or nutrients, things like sugar, fruit, and sometimes alcohol. Water that a person can drink is called "potable water" (or "drinking water"). The water in oceans is salt water, but lakes and rivers usually have unsalted water. Only about 3% of all the water on earth is fresh water. The rest is salt water.[26][27]

Drop of water falling from a faucet.

Many places, including cities and deserts, don't have as much water as people want. They build aqueducts to bring water there.

Though people can survive a few months without food, they can only survive for a day or two without water. A few desert animals can get enough water from their food, but the others must drink. Water has no smell,taste or color

Water is also used for recreational purposes, see list of water sports.

Water is used as both the coolant and the neutron moderator in most nuclear reactors. This may be ordinary water (called light water in the nuclear industry) or heavy water.

Dihydrogen monoxide parody[change | change source]

The dihydrogen monoxide parody involves calling water by the unfamiliar chemical name "dihydrogen monoxide" (DHMO) and listing some of its harmful effects in an alarming way. Some examples include talking about how "it causes burning, suffocation and corrosion," when it's actually just talking about hot water, drowning and rust. Sometimes the parody calls for it to be banned and/or labelled as dangerous.

The prank works because it takes advantage of people's misunderstanding. Calling water by an unfamiliar name and making it sound like a harmful chemical can make people think it's dangerous, if they don't know that you're just talking about water.

"Dihydrogen monoxide" is an alternative chemical name for water, but nobody uses it. The word "dihydrogen" means two hydrogens, and "monoxide" means one oxygen. Water's chemical formula has two hydrogens and one oxygen.

The parody gained most of its popularity in the 1990s, when a 14-year-old named Nathan Zohner collected anti-DHMO petitions for a science project about gullibility. Zohner fooled a lot of people, which has led to his project being used in lessons about critical thinking and the scientific method.

The website DHMO.org is a joke website which lists the harmful effects of water (DHMO), answers questions, and calls for it to be banned among other things.

The weirdness of water[change | change source]

A BBC short item explains that every molecule on Earth has existed for billions of years, and all of them came from elsewhere. Water is alien because it arrived on asteroids and comets. It is the second most common molecule in the universe. Why is it not a gas? It is made of two very light elements. Ice floating on water is also an oddity. Also, hot water freezes faster than cold, and no-one knows why this is. Molecules of water can move up against the force of gravity (that's due to surface adhesion).[28]

Water in the universe[change | change source]

Band 5 ALMA receiver is an instrument specifically designed to detect water in the universe.[29]

Much of the universe's water is produced as a byproduct of star formation.[30]

On 22 July 2011, a report described the discovery of a gigantic cloud of water vapor containing "140 trillion times more water than all of Earth's oceans combined" around a quasar located 12 billion light years from Earth. According to the researchers, the "discovery shows that water has been prevalent in the universe for nearly its entire existence".[31][32]

Water has been detected in interstellar clouds in our galaxy, the Milky Way.[33] Water probably exists in abundance in other galaxies, too. Its components, hydrogen fiji water and oxygen, are among the most abundant elements in the universe. Most other planetary systems are likely to have similar ingredients.

Related pages[change | change source]

References[change | change source]

  1. "naming molecular compounds". www.iun.edu. Retrieved 1 October 2018. Sometimes these compounds have generic or common names (e.g., H2O is "water") and they also have systematic names (e.g., H2O, dihydrogen monoxide).
  2. "Definition of Hydrol". Merriam-Webster.
  3. Riddick 1970, Table of Physical Properties, Water 0b. pg 67-8.
  4. Lide 2003, Properties of Ice and Supercooled Water in Section 6.
  5. Water in Linstrom, Peter J.; Mallard, William G. (eds.); NIST Chemistry WebBook, NIST Standard Reference Database Number 69, National Institute of Standards and Technology, Gaithersburg (MD), http://webbook.nist.gov (retrieved 2016-5-27)
  6. 6.0 6.1 Anatolievich, Kiper Ruslan. "Properties of substance: water".
  7. Lide 2003, Vapor Pressure of Water From 0 to 370° C in Sec. 6.
  8. Lide 2003, Chapter 8: Dissociation Constants of Inorganic Acids and Bases.
  9. Weingärtner et al. 2016, p. 13.
  10. "What is the pKa of Water". University of California, Davis. 2015-08-09.
  11. Silverstein, Todd P.; Heller, Stephen T. (17 April 2017). "pKa Values in the Undergraduate Curriculum: What Is the Real pKa of Water?". Journal of Chemical Education. 94 (6): 690–695. Bibcode:2017JChEd..94..690S. doi:10.1021/acs.jchemed.6b00623.
  12. Ramires, Maria L. V.; Castro, Carlos A. Nieto de; Nagasaka, Yuchi; Nagashima, Akira; Assael, Marc J.; Wakeham, William A. (1995-05-01). "Standard Reference Data for the Thermal Conductivity of Water". Journal of Physical and Chemical Reference Data. 24 (3): 1377–1381. Bibcode:1995JPCRD..24.1377R. doi:10.1063/1.555963. ISSN 0047-2689.
  13. Lide 2003, 8—Concentrative Properties of Aqueous Solutions: Density, Refractive Index, Freezing Point Depression, and Viscosity.
  14. Lide 2003, 6.186.
  15. Lide 2003, 9—Dipole Moments.
  16. 16.0 16.1 16.2 Water in Linstrom, Peter J.; Mallard, William G. (eds.); NIST Chemistry WebBook, NIST Standard Reference Database Number 69, National Institute of Standards and Technology, Gaithersburg (MD), http://webbook.nist.gov (retrieved 2014-06-01)
  17. Breaking News | Oldest rock shows Earth was a hospitable young planet. Spaceflight Now (2001-01-14). Retrieved on 2012-01-27.
  18. "United Nations". Un.org. 2005-03-22. Retrieved 2010-07-25.
  19. Kulshreshtha S.N. 1998. "A global outlook for water resources to the Year 2025". Water Resources Management. 12 (3): 167–184. doi:10.1023/A:1007957229865. |access-date= requires |url= (help)
  20. "Anomalous properties of water". lsbu.ac.uk. 2011. Retrieved September 1, 2011.
  21. "Forty-one anomalies of water « Fairy LoRe". fathersergio.wordpress.com. 2011. Retrieved September 1, 2011.
  22. "8(a) Physical Properties of Water". physicalgeography.net. 2011. Retrieved August 31, 2011. pan
  23. "Understanding the processes of erosion". mountainnature.com. 2009. Retrieved August 31, 2011.
  24. "iapws.org". iapws.org. 2000. Retrieved August 31, 2011.
  25. "Surface tension is a contractive tendency of the surface of a liquid that allows it to resist an external force". Boundless. Retrieved December 25, 2016.
  26. "Percentage of water".
  27. "Fresh water percentage (2)".
  28. Jha, Alok 2019. Why water is one of the weirdest things in the universe. BBC News Ideas. [1]
  29. "ALMA greatly improves capacity to search for water in universe". Archived from the original on 23 July 2015. Retrieved 20 July 2015.
  30. Melnick, Gary, Harvard-Smithsonian Center for Astrophysics and Neufeld, David, Johns Hopkins University quoted in: "Discover of Water Vapor Near Orion Nebula Suggests Possible Origin of H20 in Solar System (sic)". The Harvard University Gazette. 23 April 1998. Archived from the original on 16 January 2000. "Space Cloud Holds Enough Water to Fill Earth's Oceans 1 Million Times". Headlines@Hopkins, JHU. 9 April 1998. Archived from the original on 9 November 2007. Retrieved 21 April 2007. "Water, Water Everywhere: Radio telescope finds water is common in universe". The Harvard University Gazette. 25 February 1999. Archived from the original on 19 May 2011. Retrieved 19 September 2010. ("archive link". Archived from the original on 20160715. Check date values in: |archivedate= (help))
  31. Clavin, Whitney; Buis, Alan (22 July 2011). "Astronomers Find Largest, Most Distant Reservoir of Water". NASA. Archived from the original on 24 July 2011. Retrieved 25 July 2011.
  32. Staff (22 July 2011). "Astronomers Find Largest, Oldest Mass of Water in Universe". Space.com. Archived from the original on 29 October 2011. Retrieved 23 July 2011.
  33. Bova, Ben (13 October 2009). Faint Echoes, Distant Stars: The Science and Politics of Finding Life Beyond Earth. Zondervan. ISBN 978-0-06-185448-4.
  1. 1.0 1.1 Vienna Standard Mean Ocean Water (VSMOW), used for calibration, melts at 273.1500089(10) K (0.000089(10) °C, and boils at 373.1339 K (99.9839 °C). Other isotopic compositions melt or boil at slightly different temperatures.
  2. A commonly quoted value of 15.7 used mainly in organic chemistry for the pKa of water is incorrect.[10][11]

Other websites[change | change source]