Experience 5: Water and Aqueous Systems

properties of water

high surface tension and low vapor pressure

surface tension

the inward force, or pull, that tends to minimize the surface area of a liquid

surfactant

a substance that interferes with the hydrogen bonding between water molecules and thereby reduces surface tension (eg. soap and detergent)

vapor pressure

result of molecules escaping from the surface of the liquid and entering the vapor phase

ice melting point

0ºC

aqueous solution

water that contains dissolved substances

solvent

dissolving medium (like the police breaking up a fight)

solute

the dissolved particle (fighter broken up)

solutions

homogenous, stable mixtures

solvation

the process by which the positive and negative ions of an ionic solid become surrounded by solvent molecules

nearly insoluble

compounds that cannot be solvated to any significant extent

"like dissolves like"

a rule that polar solvents dissolve ionic and polar compounds, and that nonpolar solvents dissolve nonpolar compounds

electrolyte

a compound that conducts and electric current when it is in a molten state or an aqueous solution

all ionic compounds

electrolytes

nonelectrolyte

a compound that does not conduct an electric current in aqueous solutions nor molten state

strong electrolytes

most soluble salts, inorganic acids, and inorganic bases

weak electrolyte

conducts electricity poorly because only a fraction of the solute exists as ions; organic acids and bases and ammonia

suspension

a heterogeneous mixture from which particles settle out upon standing

colloid

a heterogeneous mixture containing particles that range in size; they spread throughout the dispersion medium (which can be solid, liquid, or gas) (eg. jello, smoke, paint, aerosol spray)

tyndall effect

the scattering of visible light by colloidal particles (suspensions exhibit tyndall effect, also. solutions, however, do not)

brownian motion

the chaotic movement of colloidal particles (causing flashes of light)

coagulation

when added ions neutralize the charges colloidal particles, the particle clump together

emulsion

a liquid in a liquid colloid

emulsifying agent

material added to a solid & liquid in liquid suspensions to separate the individual suspended particles (ie, soap)

Determines rates of dissolution

stirring (agitation), temperature, and the surface area

agitation

speeds up the process because fresh solvent is continually brought into contact with the solute

temperature

the higher the kinetic energy, the more the collisions and the faster solvation occurs

particle size and formation

exposing a greater surface area quickens the dissolving rate (ie grains of sugar vs. cubes)

saturated solution

contains the maximum amount of solute for a given quantity of solvent at a constant temperature and pressure (if given more it will not dissolve)

solubility

the amount of solute that dissolves in a given quantity of a solvent at a specified temperature and pressure to produce a saturated solution

solubility =

g/solute per 100 grams of solvent

unsaturated solution

contains less solute than a saturated solution at a given temperature and pressure

miscible

two liquids that dissolve each other in all proportions (such as ethylene glycol and water)

immiscible

liquids that are insoluble in one another (oil and vinegar)

supersaturated solution

contains more solute than it can theoretically hold at a given temperature

Henry's Law

at a given temperature, the solubility (S) of a gas in a liquid is directly proportional to the pressure (P) of the gas above the liquid. as P ^, S v

concentration

a measure of the amount of solute that is dissolved in a given quantity of solvent

dilute solution

contains a small amount of solute

concentrated solution

contains a large amount of solute

molarity

number of moles of solute dissolved in one liter of solution

diluting a solution

reduces the number of moles of solute per unit volume, though the total number of moles of solute does not change

colligative property

a property that depends only upon the number of solute particles, and not upon their identity

freezing-point depression

the difference in temperature between the freezing point of a solution and the freezing point of the pure solvent

boiling-point elevation

the difference in temperature between the boiling point of a solution and the boiling point of a solvent