Properties Of Water: Physical And Chemical

 Properties Of Water

What is water?

Water is the chemical substance with chemical formula H2O, one molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom. Let us learn about the physical and chemical properties of water.

Properties of Water

A glance of earth taken from space will depict it blue in color. This blue color is actually water, the major part of the earth is covered with water. We need water for almost everything, for example- drinking, bathing, cooking etc and therefore we should know about the properties of water. 65 % human body is composed of water. Water is essential for the survival of life on earth. Water is distributed unevenly on the earth’s surface. It forms a major solvent and dissolves almost every polar solute. So let us have a look at its properties and understand the reason for its significance:

Physical properties of water

Water is colorless and tasteless liquid. The molecules of water have extensive hydrogen bonds resulting to unusual properties in the condensed form. This also leads to high melting and boiling points. As compared to other liquids, water has a higher specific heat, thermal conductivity, surface tension, dipole moment etc. These properties form the reason for its significance in the biosphere. Water is an excellent solvent and therefore it helps in the transportation of ions and molecules required for metabolism. It has a high latent heat of vaporization which helps in the regulation of body temperature.

Chemical properties of water

Water reacts with a lot of substances to form different compounds. Some significant reactions are as follows:

  • Amphoteric nature:

    Water can act as both acid and base, which means that it is amphoteric in nature.
    Example:
    Acidic Behavior:               \(H_2O (l)   +  NH_3 (aq)  \) ⇌ \(   H_3O^+ (aq)     +   NH^+_4 (aq)\)
    Basic Behavior:                 \(H_2O (l)   +  H_2S (aq) \)   ⇌    \(H_3O^+ (aq)     +   HS^-   (aq)\)

  • Redox reactions:

    Electropositive elements reduce water to hydrogen molecule. Thus water is a great source of hydrogen. Let us see an example in this case:

    \(2H_2O(l) + 2Na(s) \rightarrow 2NaOH(aq) + H_2(g) \)

    During the process of photosynthesis, water is oxidized to O2. As water can be oxidized and reduced, it is very useful in redox reactions.

  • Hydrolysis reaction

    Water has a very strong hydrating tendency due to its dielectric constant. It dissolves many ionic compounds. Some covalent and ionic compounds can be hydrolyzed in water.

 

Properties
Chemical formula H2O
Molar mass 18.01528(33) g/mol
Odor None
Density Solid:

0.9167 g/ml at 0 °C

Liquid:

0.961893 g/mL at 95 °C

0.9970474 g/mL at 25 °C

0.9998396 g/mL at 0 °C

Boiling point 99.98 °C (211.96 °F; 373.13 K)
Melting  point 0.00 °C (32.00 °F; 273.15 K)

Solubility

Poorly soluble in aliphatic and aromatic hydrocarbons, ethers and Ethers.
Improved solubility in amines,  ketones, alcohols, carboxylates.
Miscible with acetonitrile, dimethyl sulfoxide, dimethoxyethane, dimethylformamide, acetaldehyde, sulfolane, tetrahydrofuran, 1,4-dioxane, glycerol, acetone, isopropanol, propanol, ethanol, methanol.
Partially miscible with Bromine, Ethyl Acetate, Diethyl ether, Dichloromethane.

Acidity (pKa) 

 

13.995
Vapor pressure 3.1690 kilopascals or 0.031276 atm
Basicity (pKb) 13.995
Refractive index(nD)  1.3330 (20°C)
Thermal conductivity 0.6065 W/m·K
Viscosity 0.890 cP
Structure
Crystal structure Hexagonal
Molecular shape Bent
Point group C2v
Dipole moment 1.8546 D
Thermochemistry
Specific heat capacity (C) 75.375 ± 0.05 J/mol·K
Std enthalpy of formationfHo298) -285.83 ± 0.040 kJ/mol
Std molar entropy (So298 69.95 ± 0.03 J/mol·K
Gibbs free energyfG˚) -237.24 kJ/mol

We have seen the physical and chemical properties of water and understood its importance. There is a lot more to explore and understand about water. If you are curious to know further, kindly install Byju’s -the learning app.


Practise This Question

The critical temperature of water is higher than that of O2 because H2O molecule has