Effect of Various Solutes on Surface Tension and Viscosity
The addition of solutes can change both surface tension and viscosity depending on their chemical nature. Surfactants typically decrease surface tension, salts usually increase it, polymers raise viscosity, and salts may either increase or lower viscosity depending on their interaction with water molecules.
Effect of Solute on Surface Tension
The addition of solutes to a liquid can either increase or decrease the surface tension.
Surfactants (surface-active agents): Surfactants decrease surface tension because, the hydrophilic groups of the surfactants interact with the water molecules at the surface of the liquid, while the hydrophobic groups interact with the air molecules. This interaction disrupts the hydrogen bonding between the water molecules and decreases the surface tension.
Inorganic salts (electrolytes): Inorganic salts increase surface tension because, the ions in the salt interact with the water molecules and decreases their mobility. The decreased mobility of the water molecules prohibit them to break away from the surface of the liquid and form droplets, which increase the surface tension.
Organic solutes (alcohols, sugars): Low molecular weight alcohols (like ethanol) reduce surface tension, but larger sugars and polyols often increase it slightly due to hydrogen bonding stabilization.
Effect of Solute on Viscosity
The addition of solutes to a liquid can either increase or decrease the viscosity.
Polymers: The addition of long-chain polymer molecules increase the viscosity because, the polymers interact with each other and form a complex or giant structure, which make it more difficult for the liquid to flow.
Inorganic salts: The addition of inorganic salts to a liquid generally decreases the viscosity because, the ions in the salt interact with the water molecules and decreases their mobility.
Molecular solutes (sugars, glycerol, alcohols): Sugars and polyhydric alcohols increase viscosity because of their ability to form hydrogen-bonded networks with water. Low molecular weight alcohols like ethanol usually decrease viscosity due to disruption of the water structure.
Applications of Effect of Solutes on Surface Tension and Viscosity
Surfactants: Detergents, paints, foams, emulsification, textile wetting and dyeing.
Polymers: Food thickeners (sauces, jams), pharmaceuticals (gels, suspensions), cosmetics (lotions, creams).
Salts: Control physical properties in industrial processes, formulations of electrolytes for batteries, stabilizing proteins in biochemistry.