Critical Temperature and Pressure for CO2 Supercritical Fluids
Definition:
Critical temperature: The temperature above which a substance cannot exist as a liquid, regardless of pressure.
Critical pressure: The minimum pressure required to maintain a substance in its liquid state at its critical temperature.
Properties of Supercritical CO2:
Acts as an attractive solvent.
Capable of dissolving materials that are normally insoluble in other solvents.
Commonly used to extract substances such as:
Caffeine from coffee.
Food flavorings, maintaining the integrity of flavor while removing caffeine.
Example:
In the extraction process, supercritical CO2 efficiently dissolves caffeine while preserving the flavors characterizing coffee.
Surface Tension
Definition:
Surface tension is the energy required to increase the surface area of a liquid substance.
Less formally, it can be described as the energy needed to "break" the surface of the liquid.
Molecular Behavior:
Molecules located at the surface behave differently compared to those situated in the liquid's interior.
Surface molecules experience a net inward force of attraction due to the lack of neighboring liquid molecules above them, resulting in an energized surface layer.
Capillary Action
Definition:
Capillary action is defined as the movement of liquid within a narrow space, such as a capillary tube, against the force of gravity.
Key Factors:
Intermolecular forces contribute to the capillary action phenomenon.
The movement results in the formation of a concave meniscus in water columns.
Cohesive and Adhesive Forces:
Cohesive Forces:
Intermolecular forces that bind similar molecules to each other.
Adhesive Forces:
Intermolecular forces that bind a substance to a surface.
Meniscus Behavior:
When cohesive forces dominate adhesive forces, a convex meniscus forms.
Conversely, when adhesive forces are stronger than cohesive forces, a concave meniscus occurs.
Example: When water rises in a paper, it is due to the adhesive forces between water molecules (H-bonds) and the hydroxyl (OH) groups of cellulose in the paper.
Viscosity
Definition:
Viscosity is defined as the resistance of a liquid to flow.
Relation to Molecular Movement:
Viscosity is related to how easily individual liquid molecules move relative to one another.
Temperature Dependence:
Viscosity generally decreases with increasing temperature, as higher temperatures facilitate molecular movement.
Measurement Method:
Viscosity can be quantified by observing the rate at which a solid object descends through the liquid:
A lower rate or longer time for an object to fall indicates higher viscosity.