Water (molecule)

Water (H2O)
General
Systematic name	Water
Other names	Aqua Hydrogen oxide Hydrogen hydroxide Hydrate Oxidane Hydric acid Dihydrogen monoxide Hydrohydroxic acid μ-Oxido dihydrogen
Molecular formula	HOH or H2O
Molar mass	18.01524 g·mol−1
Appearance	transparent, almost colorless liquid with a slight hint of blue[1]
CAS number	[7732-18-5]
see also	Water (data page)
Properties
Density and phase	1000 kg·m−3, liquid (4 °C) 917 kg·m−3, solid
Melting point	0 °C, 32 °F (273.15 K)[2]
Boiling point	100 °C, 212 °F (373.15 K)[2]
Triple point	273.16 K, 611.73 Pa
Critical point	647 K, 22.1 MPa
Specific heat capacity (gas)	cp=1970 J·kg−1·K−1 @ 300 K cv=1510 J·kg−1·K−1 @ 300 K[3]
Specific heat capacity (liquid)	4186 J·kg−1·K−1
Specific heat capacity (solid)	2060 J·kg−1·K−1
Acidity (pKa)	15.74
Basicity (pKb)	15.74
Viscosity	0.001 Pa·s at 20 °C
Surface Tension at 20 °C	7.28 N·m−1
Structure
Molecular shape	non-linear bent
Crystal structure	Hexagonal See ice
Dipole moment	1.85 D
Hazards
MSDS	External MSDS
Main hazards	Drowning
NFPA 704	0 0 0
RTECS number	ZC0110000
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Related compounds
Related solvents	acetone methanol
Related compounds	water vapor ice heavy water
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Water (H₂O, HOH) covers 70-75% of the Earth's surface in its liquid and solid (ice) states, and is present in the atmosphere as a vapor. It is the most abundant molecule on the Earth's surface.^[4]

At room temperature, it is a nearly colorless, flavorless, and odorless liquid. Many substances dissolve in water and it is commonly seen as the universal solvent; because of this, water in nature and in use is rarely clean, and may have some properties different than those in the laboratory. But there are many compounds that are essentially, if not completely, insoluble in water. Water is the only common, pure substance found naturally in all three states of matter—for other substances, see Chemical properties.

Pure water is tasteless. It is the other chemicals in the water which may give water a flavour.

1. ↑ Braun C.L & Smitnov S.N. 1993. Why is water blue? J. Chem Ed. 70, 612. [1] Archived 2019-05-25 at the Wayback Machine
2. ↑ ^{2.0 2.1} 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)
3. ↑ Serway, Raymond A. Physics for scientists and engineers, 3rd edition
4. ↑ Water chemistry [2] Archived 2011-10-21 at the Wayback Machine