Properties of Water

Interesting Facts and Properties of Water

Water is one of the most important molecules in chemistry, particularly biochemistry since water is essential for life.
Water is one of the most important molecules in chemistry, particularly biochemistry since water is essential for life. Toshiro Shimada / Getty Images

Water is the most abundant molecule on the Earth's surface and one of the most important molecules to study in chemistry. Here's a look at some facts about water chemistry.

What Is Water?

Water is a chemical compound. Each molecule of water, H2O or HOH, consists of two atoms of hydrogen bonded to one atom of oxygen.

Properties of Water

There are several important properties of water that distinguish it from other molecules and make it the key compound for life:

  1. Cohesion is a key property of water. Because of the polarity of the molecules, water molecules are attracted to each other. Hydrogen bonds form between neighboring molecules. Because of its cohesiveness, water remains a liquid at normal temperatures rather than vaporizing into a gas. Cohesiveness also leads to high surface tension. An example of the surface tension is seen by beading of water on surfaces and by the ability of insects to walk on liquid water without sinking.
  2. Adhesion is another property of water. Adhesiveness is a measure of water's ability to attract other types of molecules. Water is adhesive to molecules capable of forming hydrogen bonds with it. Adhesion and cohesion lead to capillary action, which is seen when the water rises up a narrow glass tube or within the stems of plants.
  3. The high specific heat and high heat of vaporization mean a lot of energy is needed to break hydrogen bonds between water molecules. Because of this, water resists extreme temperature changes. This is important for weather and also species survival. The high heat of vaporization means evaporating water has a significant cooling effect. Many animals use perspiration to keep cool, using this effect.
  1. Water may be called the universal solvent because it is able to dissolve many different substances.
  2. Water is a polar molecule. Each molecule is bent, with the negative charged oxygen on one side and the pair of positive-charged hydrogen molecules on the other side of the molecule.
  3. Water is the only common compound that exists in solid, liquid, and gas phase under ordinary, natural conditions.
  4. Water is amphoteric, which means it can act as both an acid and a base. Self-ionization of water produces H+ and OH- ions.
  5. Ice is less dense than liquid water. For most materials, the solid phase is denser than the liquid phase. Hydrogen bonds between water molecules are responsible for the lower density of ice. An important consequence is that lakes and rivers freeze from the top down, with ice floating on water.

Water Facts

  • Other names for water are: dihydrogen monoxide, oxidane, hydroxylic acid, and hydrogen hydroxide
  • the molecular formula of water: H2O
  • molar mass of water: 18.01528(33) g/mol
  • density 1000 kg/m3, liquid (4 °C) or 917 kg/m3, solid. This is why ice floats on water.
  • melting point: 0 °C, 32 °F (273.15 K)
  • boiling point: 100 °C, 212 °F (373.15 K)
  • acidity (pKa): 15.74
  • basicity (pKb): 15.74
  • refractive index: (nD) 1.3330
  • viscosity: 0.001 Pa s at 20 °C
  • crystal structure: hexagonal
  • molecular shape: bent
  • Pure liquid water at room temperature is odorless, tasteless and nearly colorless. Water has a faint blue color, which becomes more apparent in large volumes of water.
  • Water has the second highest specific enthalpy of fusion of all substance (after ammonia). The specific enthalpy of fusion of water is 333.55 kJ·kg−1 at 0 °C.
  • Water has the second highest specific heat capacity of all known substances. (Ammonia has the highest specific heat.) Water also has a high heat of vaporization (40.65 kJ·mol−1). The high specific heat and heat of vaporization result from the high degree of hydrogen bonding between water molecules. One consequence of this is that water is not subject to rapid temperature fluctuations. On Earth, this helps to prevent dramatic climate changes.