Liquids and Solutions: Properties, Characteristics, and Behavior
Liquids and Solutions
Liquids:
Liquids are substances found in a fluid state, where molecules, atoms, or particles are linked. They can move freely within the solution but cannot escape it. Key characteristics include:
- Intermolecular attraction forces are strong enough to keep molecules close to each other.
- Liquids are denser and less compressible than gases.
- Liquids have a definite volume independent of the shape and size of the container.
- Attractive forces are not strong enough to keep molecules in a fixed position, allowing them to move.
- Liquids can be poured and take the shape of their container.
Properties:
Surface Tension:
The amount of energy needed to increase the surface area of a liquid by a unit area.
Vapor Pressure:
The pressure exerted by a vapor in dynamic equilibrium with its liquid at a given temperature.
Boiling Point:
The temperature at which the vapor pressure of a liquid equals the external atmospheric pressure.
Freezing Point:
The temperature at which the liquid and solid phases of a substance coexist in equilibrium.
Viscosity:
A liquid’s resistance to flow, related to the magnitude of intermolecular attractive forces and, in some cases, the size of the molecules.
Density:
The physical property that describes the mass of a substance per unit volume.
Capillary Action:
A property of liquids resulting from the interplay of cohesive forces (attraction between similar molecules) and adhesive forces (attraction between different molecules). When adhesion is stronger than cohesion, the liquid rises in a capillary.
Phase Diagram:
A graphical representation of the conditions of temperature and pressure at which solids, liquids, and gases (vapors) exist as single phases or in equilibrium. Key features include:
- Different regions correspond to a single phase of the substance.
- Lines or curves represent two phases in equilibrium.
- Phase diagrams describe the effects of pressure and temperature on the phases of a substance.
Vapor Pressure Curve:
Represents the boundary between the gaseous and liquid phases of a substance. It shows the vapor pressure of a substance at a given temperature.
Critical Point:
The temperature above which a gas cannot be liquefied, regardless of pressure. Kinetic energy is greater than attractive interactions.
Sublimation Curve:
Represents the boundary between the solid and gaseous phases, indicating the vapor pressure of a solid at different temperatures.
Evaporation Curve:
Represents the boundary between the liquid and solid phases, indicating the melting point as a function of pressure. For most substances, the solid phase is denser than the liquid phase.
Triple Point:
The specific temperature and pressure at which all three phases of a substance coexist in equilibrium.
Supercritical Fluid:
A state located above the critical point, where liquid and gas phases are indistinguishable.
Solutions:
Solution:
A uniform mixture of two or more substances with constant composition and uniform properties.
Solvent:
The substance present in the greatest concentration in a mixture.
Solute:
The component present in a smaller amount in a mixture, which is dissolved in the solvent.
Units of Physical and Chemical Concentration:
Weight/Weight Percentage:
The relative number of parts by weight of solute per 100 parts of solution.
% Weight/Weight = (Weight of solute / Weight of solution) x 100
Weight/Volume Percentage:
The relative number of parts by weight of solute per volume of solution.
% Weight/Volume = (Weight of solute (g) / Total volume (ml)) x 100
Volume/Volume Percentage:
The relative number of parts by volume of solute per total volume of solution.
% Volume/Volume = (Volume of solute / Total volume) x 100
Parts per Million (ppm):
Milligrams of solute per liter of solution or 1 gram of solute per 1,000,000 grams of solution.
Parts per Billion (ppb):
Micrograms of solute per liter of solution or 1×10-6 g of solute per 1,000,000,000 grams of solution.
Molarity (M):
Moles of solute per liter of solution.
M = Moles of solute / Liter of solution
Molality (m):
Moles of solute dissolved in 1 kg of solvent.
m = Moles of solute / Mass of solvent (kg)
Preparation of Solutions:
Solutions are prepared by:
- Measuring the appropriate amounts of solute and solvent (by weight or volume).
- Mixing the measured amounts.
- Diluting a solution of known concentration.
The following expression can be used to calculate one of four quantities when the other three are known:
c1 * v1 = c2 * v2
Solubility:
The maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature.
Solubility Curve:
A chart representing the variation of solubility with temperature, typically plotted with grams of solute per 100 g of water versus temperature.
Mole Fraction:
The ratio of moles of a substance to the total moles in a solution.
X = Moles of solute / Total moles