Properties of water

Water (H2O) is a polar inorganic compound that is at room temperature a tasteless and odorless liquid, which is nearly colorless apart from an inherent hint of blue. It is by far the most studied chemical compound[19] and is described as the "universal solvent"[20] and the "solvent of life".[21] It is the most abundant substance on the surface of Earth[22] and the only common substance to exist as a solid, liquid, and gas on Earth's surface.[23] It is also the third most abundant molecule in the universe (behind molecular hydrogen and carbon monoxide).[22]

The water molecule has this basic geometric structure
Ball-and-stick model of a water molecule
Ball-and-stick model of a water molecule
Space filling model of a water molecule
Space filling model of a water molecule
A drop of water falling towards water in a glass
IUPAC name
Systematic IUPAC name
Other names
Hydrogen hydroxide (HH or HOH), hydrogen oxide, dihydrogen monoxide (DHMO) (systematic name[1]), dihydrogen oxide, hydric acid, hydrohydroxic acid, hydroxic acid, hydroxylic acid, hydrol,[2] μ-oxido dihydrogen, κ1-hydroxyl hydrogen(0)
3D model (JSmol)
RTECS number
  • ZC0110000
  • InChI=1S/H2O/h1H2 checkY
  • O
Molar mass 18.01528(33) g/mol
Appearance Almost colorless or white crystalline solid, almost colorless liquid, with a hint of blue, colorless gas[3]
Odor Odorless
Density Liquid:[4]
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) [lower-alpha 1]
Boiling point 99.98 °C (211.96 °F; 373.13 K)[6][lower-alpha 1]
Solubility Poorly soluble in haloalkanes, aliphatic and aromatic hydrocarbons, ethers.[7] 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 at 25 °C[8]
Acidity (pKa) 13.995[9][10][lower-alpha 2]
Basicity (pKb) 13.995
Conjugate acid Hydronium H3O+ (pKa = 0)
Conjugate base Hydroxide OH (pKb = 0)
Thermal conductivity 0.6065 W/(m·K)[13]
1.3330 (20 °C)[14]
Viscosity 0.890 mPa·s (0.890 cP)[15]
1.8546 D[16]
75.385 ± 0.05 J/(mol·K)[17]
69.95 ± 0.03 J/(mol·K)[17]
−285.83 ± 0.04 kJ/mol[7][17]
−237.24 kJ/mol[7]
Occupational safety and health (OHS/OSH):
Main hazards
Avalanche (as snow)

Water intoxication
(see also Dihydrogen monoxide parody)

GHS labelling:[18]
NFPA 704 (fire diamond)
Flash point Non-flammable
Safety data sheet (SDS) SDS
Related compounds
Other cations
Hydrogen sulfide
Hydrogen selenide
Hydrogen telluride
Hydrogen polonide
Hydrogen peroxide
Related solvents
Supplementary data page
Water (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Water molecules form hydrogen bonds with each other and are strongly polar. This polarity allows it to dissociate ions in salts and bond to other polar substances such as alcohols and acids, thus dissolving them. Its hydrogen bonding causes its many unique properties, such as having a solid form less dense than its liquid form,[lower-alpha 3] a relatively high boiling point of 100 °C for its molar mass, and a high heat capacity.

Water is amphoteric, meaning that it can exhibit properties of an acid or a base, depending on the pH of the solution that it is in; it readily produces both H+
and OH
ions.[lower-alpha 3] Related to its amphoteric character, it undergoes self-ionization. The product of the activities, or approximately, the concentrations of H+
and OH
is a constant, so their respective concentrations are inversely proportional to each other.[24]

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