 
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. This blue colour 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 a colourless and tasteless liquid. The molecules of water have extensive hydrogen bonds resulting in 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:
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Amphoteric nature:
Water can act as both acid and base, which means that it is amphoteric in nature.
Example:
Acidic Behaviour:              \(H_2O (l)  + NH_3 (aq) \) ⇌ \(   H_3O^+ (aq)    +  NH^+_4 (aq)\)
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.
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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 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Odour | 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 |
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| Boiling point | 99.98 °C (211.96 °F; 373.13 K) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Melting  point | 0.00 °C (32.00 °F; 273.15 K) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Solubility |
Poorly soluble in aliphatic and aromatic hydrocarbons, ethers and Ethers. |
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| Acidity (pKa)Â
|
13.995 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Vapour 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 formation (ΔfHo298) | -285.83 ± 0.040 kJ/mol | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Std molar entropy (So298) | 69.95 ± 0.03 J/mol·K | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Gibbs free energy(ΔfG˚) | -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 learn about water. If you are curious to know further, kindly install BYJU’S – The Learning App.
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