Physical Properties of Water

The Physical Properties of water which influences the many soils process are

a. Polarity:

• Water molecule shows polarity due to its asymmetrical arrangement of hydrogen and oxygen atoms in which charges are not evenly distributed.
• Water is polar due to its asymmetrical structure, with a positively charged hydrogen side and a negatively charged oxygen side.
• This polarity causes water molecules to form chain-like structures (polymerization) through hydrogen bonding.
• Water is attracted to charged ions (e.g., H⁺, Na⁺, K⁺, Ca²⁺) and colloidal surfaces, forming hydrated ions and soil solutions.
• Negatively charged clay attracts the positive end of water molecules.
• Polarity helps dissolve salts because water molecules attract ions more strongly than ions attract each other.
• The hydration of ions or wetting of clay releases energy as heat of solution or heat of wetting, respectively.

b. Hydrogen Bonding:

• Hydrogen bonding accounts for two forces i.e. cohesion and adhesion which are responsible for the movement and retention of water in soils.
• The attraction of water molecules for each other is called cohesion and attraction of water molecules for the solid surfaces is called the adhesion.
• By adhesion some water molecules are held rigidly at the soil solid surfaces in turn these tightly bound water molecules by cohesion.
• The forces of adhesion and cohesion together make it possible for the soil solids to retain water and control its movement and use.

c. Surface Tension:

• In order to bring the water molecules from bulk volume of water to the surface against the inward attractive force, extra energy is required. This amount of extra energy required is called surface tension and expressed in force per unit length.

d. Contact Angle:

• When the fluid phases (liquid and gases) come in contact with soil solid, the interface between air and water forms a definite angle called contact angle.
• When the liquid wets the solid (soils) the contact angle is acute and the liquid meniscus is convex, when it does not, the contact angle is obtuse and the meniscus is concave.
• When adhesive force (water soil) >cohesive force (water-water) >adhesive force (soil-air), the contact angle becomes acute and water will wet the soil and vice-versa in obtuse angle of contact.

e. Capillarity:

• Capillarity is ability of a liquid to flow through the small spaces, known as capillaries, without any external support and against gravity.
• The capillary rise is the result of adhesive and cohesive forces acting against the gravitational pull.

f. Viscosity:

• Viscosity of a fluid is the measure of its resistance to flow. Resistance to flow, or viscosity, is higher for molecules that cause more internal friction during flow.
• It is defined as the ratio of the drag force and the velocity gradient perpendicular to the direction of flow.
• Viscosity decreases with increasing temperature.

g. Density of Water:

• When the temperature of water decreases initially from higher temperature to 4 degree centigrade, the density increases and further temperature down decreases the density of water due to expansion between the water molecules.

h. Osmotic Pressure: 

• Osmotic pressure is a property of solutions, expressing the decrease of the potential energy of water in solution relative to that of pure water.
• In dilute solutions, the osmotic pressure is generally proportional to the concentration of the solution and to its temperature

i. Solubility of gases:

• The concentration of gases in water generally increases with pressure and decreases with temperature.