Water is a tasteless and odorless liquid, which is colorless apart from an inherent hint of blue color. Due to weak absorption bands of wavelength 750 nm, it appears to be blue. Water is a major chemical component on our planet which is necessary for all living beings. It is the most abundant liquid on the earth. Almost 70% of our earth’s surface is covered by water. It is the 3rd most abundant molecule in the universe after molecular hydrogen and carbon monoxide. It is a universal solvent or the solvent of life. The molecular formula of water is H2O. Properties of Water: Due to its structure, it has very unique and useful properties.
Water is the only natural substance which is found in all 3 states: solid, liquid and gas. Triplet point is defined as the temperature at which water exists in all states, at the same time.
Pure water that is actually not available (even deionized water is not completely free of ions) is an insulator of electricity. However, water conducts if some specific substances get added to it.
Water has ability to absorb much much heat before rising its own temperature.
Structure of water
As compared to the other molecules, the water structure is very small. It consists of 2 hydrogen atoms which are bound to an oxygen atom, through the covalent bonds. Since, electrons are shared in covalent bonds, in case of water, 1 electron is required to each hydrogen atom to fill its outer shell and 2 electrons are needed by oxygen to satisfy its valence shell. So these covalent bonds fulfil the needs of all atoms in water.
Polar nature of water
Water molecules are polar in nature. Polar molecules mean the molecules which have uneven distribution of charge. When ionic molecules are placed into the water they get dissociated into ions. The polar nature of water molecules can be understood below:
Since the electrons in water are shared by covalent bonds, but actually these electrons are not equally shared by oxygen and hydrogen. These electrons lie closer to oxygen nucleus. The reason is that the oxygen nucleus has more protons i.e. more positive charge, as compared to hydrogen nucleus, so electron pair gets attracted more by O-nucleus.
As the result of this unequal sharing, electrons in the oxygen atom get polar and slightly negative, making hydrogen atoms slightly positive.
This uneven distribution of charge in water makes it a polar molecule.
Since water has 2 hydrogen atoms, so it is termed as dipolar molecule.
Hydrogen bonds in water
Basically, hydrogen bonding in water is caused by its polar nature. The slightly positive hydrogen atoms, from one water molecule, gets attracted towards the slightly negative oxygen nucleus of the other water molecule. This attraction is named as the hydrogen bonding of water. This attraction is weaker than the covalent bonds but it is one of strongest intermolecular force.
Water makes these hydrogen bonds within itself. These hydrogen bonds provide enough stability to water that a large amount of energy is required to raise the temperature of water.
Solvent: Water is a good solvent. Due to its dipolar nature, it allows polar molecules to get dissolved easily into it e.g. amino acids, salts, sugar etc.
Polar molecules are named as hydrophilic as they are water loving molecules, like salts and sugar.
Non-polar molecules are water hating molecules, like lipids. They are named as hydrophobic molecules.
Heat capacity: Heat capacity is defined as the amount of energy required to raise the temperature of 1g by 1oC. The heat capacity of water is 4.2 Joule per Kelvin i.e. it will take 4.2 J heat to raise the temp. of water by one unit. This is definitely a high value, which keeps the water stable in all environments.
The tendency of water molecules to remain stuck with each other, is known as cohesion.
Density: Density of water is 1 g per centimeter cube. Density has direct relation with temperature, but not linearly in case of water, initially, density rises with temp. and then decreases. Ice is 9% less dense than water i.e. volume of ice is 9% greater than that of water.
The amazing property of water is that in solid form (ice), its density is less as compared to its liquid form. This property makes it really different from other molecules. Aquatic organisms are able to survive in freezing sub-zero temperature in lakes and ponds due to this unique property of water.
Latent heat of vaporization: Latent heat of vaporization is defined as the amount of hear required to change the state from liquid to gas. The latent heat of vaporization for water is high (540 cal/g), so it will take more energy to change water into vapors. This is due to the hydrogen bonding b/w water molecules.
Surface tension and cohesion: Surface tension is the attractive force which pulls the fluid surface to shrink into a minimum surface area. Surface tension of water is 71.99 mN/m. Due to surface tension, skaters can walk on water and insects float on water surface, even they are denser than water. Surface tension is also responsible for capillary action.
Cohesion means the attraction of molecules for other molecules which are of same kind.
Adhesion means attraction of molecules for those molecules which are of different kind.
Properties of Water: Water is highly cohesive as well as adhesive. The hydrogen bonding in water molecules allows them to stick with each other, thus water is cohesive. Cohesive force is responsible for surface tension. Due to the adhesive properties of water, it sticks to substances other than itself.
pH: pH stands for potential of hydrogen. It measures that much acidic or basic the water is. Usually its range is 0 to 14, with 7 as natural. pH less than 7 indicates acidity and greater than 7 means a base. Water itself is a source of H+ ions and usually has pH b/w 6.5 to 8.5.
Ionization: Ionization means the splitting of molecules to their cations and anions. For example, when we mix salt (NaCl) to water, they split into ions (Na++ and Cl-), thus salt gets dissolved. Water also gets self-ionized as shown below:
Boiling and freezing point: Water has boiling point of 100 degree Celsius, which is relatively high and it freezes at zero degree Celsius. In winter, the top layer of water in lakes freezes, but under that layer water is in liquid state, due to which aquatic organisms remain alive, even in winter.
Amphoteric: Water is amphoteric, mean it can act as both acid and base, depending upon the pH of the solution in which water is present. It can produce both H+ and OH- ions. It also undergoes self-ionization.
Importance of water
Water’s physical characteristics are vital for life and nature on Earth. Water is so abundant on Earth that its physical properties have a significant effect on Earth’s physics in general. Water occupies nearly three quarters of the surface of the earth. It is the only natural chemical material within the normal temperature spectrum of the Planet that occurs as liquid, solid (ice), and gas (water vapor). Water is liquid (0-100 ° C, 32-212 ° F) in a range important for biological life, and liquid water is present almost everywhere on Earth. The capacity of water to retain heat controls the environment and weather on Earth.
Besides its versatile applications in ever field, it is very necessary for human body. It carries nutrients to all body cells. It provides oxygen to our brain. Our body absorbs vitamins, amino acids, glucose and other minerals due to water. It helps our body to flush out all toxins and waste. It also helps to regulate the temperature of our body. It acts like a lubricant for muscles and joints. In other words, it is completely right that life can’t exist without water.