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Felix qui potuit rerum cognoscere causus

Space filling model of water

Water - H2O

molecular mass 18.02 g/mol
boiling point (1 atm)  373 K
density (277.13K) 1.000 g/mL
acid dissociation constant 1 X 10-14
heat capacity 4.18 J/K mol
total amount in Earth's mantle 2 X 1023 kg

Water makes up most of the mass of most living things, including humans. Water is the solvent of choice for most ionic reactions, for many acids and bases, and is used in large quantities in many industrial processes.

Chemically, it has some unusual properties. Hydrogen bonding between adjacent molecules causes it to have a higher than expected boiling point and high viscosity, as well as resulting in expansion upon freezing.

In first-year chemistry courses, chemical equilibria, solution reactions and acid-base properties are all discussed in terms of substances dissolved in water. This is because water is the most commonly encountered solvent, and because it is the solvent in all biological processes.



Evidence of water-erosion on Mars

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A recent NASA photo of the surface of Mars showing features that are thought to have been caused by liquid water.

more info on Mars exploration


a lot of water

tropical weather and hurricanes

hurricane center at NOAA

More information

biochemistry and water

water chemistry in detail