Cap 13

mixtures

two or more substances mixed together physically, not combined chemically

solution

a homogeneous mixture of two or more substances. it exists as one phase

solvent

the substance in which other substances are dissolved

• the most abundant component in the solution

solute

the substance that dissolves in a solvent

solubility

the maximum amount of the solute that dissolves in a fixed quantity of a given solvent at a given temperature when an excess of the solute is present

concentrated

a relatively large amount of solute dissolved in a given quantity of solvent

dilute

a relatively small amount of solute in a given quantity of solvent

miscible

solute and solvent that are soluble in each other in any proportion

• generally applied to solutions in which both solutes and solvents are liquids or gases

immiscible

liquids that do not dissolve in each other

like dissolves like rule

substances with similar types of intermolecular forces dissolve in each other

ion dipole forces

attractions between ions and polar molecules

• the principle force involved when an ionic compound dissolves in water

hydration shells

as an ion separates from the crystal structure water molecules cluster around it in this forms

hydrogen bonding

attractions between molecules with an H atom bonded to N, O or F

• the principle force in solutions of polar O and N containing organic and biological compounds such as alcohols, amines and amino acids

dipole dipole forces

attractions between polar molecules

• in the abscence of H bonding, allow polar molecules to dissolve in polar solvents

ion induced dipole forces

occur when the charge of an ion causes a distortion in the electron cloud of a nonpolar particle

• a cation pulls the nonpolar particles electron cloud density towards it while an anion pushes electron density away from it

dipole induced dipole forces

arise when a polar molecule distorts the elctron cloud of a nonpolar molecule

alcohol

organic compounds that have a dual polarity, a polar hydroxyl group bonded to a nonpolar hydrocarbon group

soap

the salt formed when a strong base reacts with a fatty acid

alloys

mixtures of elements that have a metallic character

substitutional alloys

a type of alloy in which atoms of one element replace atoms of the main element at some sites in the cubic closest packed array

interstitial alloy

types of alloys that occur when atoms of a no metal fill some spaces between atoms of the main element in the body centered array

heat of solution

the total enthalpy change that occurs when solute and solvent form a solution

solvation

the process of surrounding a solute particle with solvent particles

hydration

solvation in water

heat of hydration

enthalpy changes for separating the water molecules and mixing the separated solute with them

charge density

the ratio of an ions charge to its volume

coulumbs law

the higher the charge of an ion and the smaller its radius, the closer it gets to the oppositely charges pole of a water molecule and the stronger the attraction between the ion and the water molecule

entropy

a thermodynamic variable

• directly related to the number of ways a system can distribute its energy, which involves the freedom of motion of the particles

saturated solution

a solution that is at equilibrium and contains the maximum amount of dissolved solute at a given temperature in the presence of undissolved solute

unsaturated solution

contains less than the equilibrium concentration of dissolved solute

supersaturated solution

contains more than the equilibrium concentration and is unstable relative to the saturated solution

henrys law

expresses the quantitative relationship between gas pressure and solubility: the solubility of a gas is directly proportional to the partial pressure of the gas above the solution

concentration

the proportion of a substance in a mixture

intensive property

a property that does not depend on the quantity of a mixture

molarity

the number of moles of solute dissolved in 1 Liter of solution

molality

the number of moles of solute dissolved in 1kg of solvent

mass percent

mass of solute dissolved in 100 parts by mass solution

volume percent

the volume of solute in 100 volumes of solution

mole fraction

the ratio of the number of moles of solute to the total number of moles

mole percent

the mole fraction expressed as a percentage

colligative properties

four important properties in which the number of solute particles gives a solution different physical properties than the pure solvent has:

• vapor pressure lowering

• boiling point elevation

• freezing point depression

• osmotic pressure

strong electrolyte

an aqueous solution of this electrolyte conducts a current very well because the solute dissociates completely into ions as it dissolves

• soluble ionic compounds

• strong acids

• strong bases

weak electrolytes

an aqueous solution of this electrolyte conducts poorly beacause the solute dissociates very little as it dissolves to produce very few ions

• weak acids

• weak bases

nonelectrolytes

molecular compounds such as sugar and alcohol that do not dissociate into ions at all. their solutions do not conduct a current

nonvolatile nonelectrolytes

these solutions contain solutes that are not ionic and thus does not dissociate and they have negligible vapor pressure at the boiling point of the solvent

vapor pressure lowering

the vapor pressure of a solution whose solute is a no volatile nonelectrolyte is always lower than the vapor pressure of the pure solvent

raoults law

says that the vapor pressure of solvent above a solution equals the mole fraction of solvent times rhe vapor pressure of the pure solvent

ideal solution

one that follows raoults law at any concentration

boiling point elevation

the boiling point of a solution is always higher than the boiling point of the pure solvent

freezing point depression

the freezing point of a solution is always lower than the freezing point of the pure solvent

freezing point

when solid solvent and liquid solution are in equilibrium

semipermeable membrane

a membrane that allows solvent but not solute to pass through

osmosis

a net flow of solvent into the more concentrated solution that causes a pressure difference known as osmotic pressure

osmotic pressure

a pressure difference. the pressure that must be applied to prevent net movement of water from solvent to solution

fractional distillation

a laboratory method in which a solution of two or more volatile components is attached to a fractionating column packed with glass beads

ionic atmosphere

positive ions clustered near negative ions and vice versa