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]

"HOH" redirects here. For other uses, see HOH (disambiguation).
For broader coverage of this topic, see Water.
Water
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
Names
IUPAC name
Water
Systematic IUPAC name
Oxidane
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)
Identifiers
3D model (JSmol)
3587155
ChEBI
ChEMBL
ChemSpider
117
RTECS number
  • ZC0110000
UNII
  • InChI=1S/H2O/h1H2 checkY
    Key: XLYOFNOQVPJJNP-UHFFFAOYSA-N checkY
  • O
Properties
H
2O
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
Solid:[5]
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]
Structure
Hexagonal
C2v
Bent
1.8546 D[16]
Thermochemistry
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]
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Drowning
Avalanche (as snow)


Water intoxication
(see also Dihydrogen monoxide parody)

GHS labelling:[18]
[?]
NFPA 704 (fire diamond)
0
0
0
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
 Acetone
Methanol
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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