chapter 13: properties of solutions

solute

the substance that is being dissolved in a solution

solvent

the substance that dissolves the solute; usually the greatest amount

solution

a homogeneous mixture of two or more substances

aqueous solution

a solution in which water is the solvent

gas solution- example

air- oxygen dissolved in nitrogen

liquid solution- example

vinegar- acetic acid in water

solid solution- example

brass- zinc dissolved in copper

what are three key traits of a solution?

homogeneous, stable, solute particles are very small

what are the three steps in the solution formation process?

• Break solute-solute interactions (endothermic)

• Break solvent-solvent interactions (endothermic)

• Form solute-solvent interactions (exothermic)

which steps of solution formation are endothermic?

formation of solute-solvent interactions

which step of solution formation is exothermic?

formation of solute-solvent interactions

how does entropy relate to solution?

entropy increases favoring the formation of a solution due to greater disorder

like dissolves like

polar solvents dissolve polar solutes; nonpolar solvents dissolve nonpolar solutes

non-electrolyte

a compound that dissolves in water as molecules and does not conduct electricity

electrolyte

compound that dissolves in water and forms ions, conducting electricity

strong electrolyte

compound that completely dissociates into ions in solution

weak electrolyte

a compound that partially dissociates in solution

ionic electrolyte

ionic compound that dissociates into positive and negative ions in solution (NaCl)

covalent electrolyte

molecular compound that ionizes in water, like acids

difference in dissolution between non-electrolytes and strong electrolytes

non-electrolytes stay intact as molecules; strong electrolytes dissociate into ions

solubility

maximum amount of solute that can dissolve in a solvent at a specific temp

unsaturated solution

contains less solute than the solvent can dissolve

saturated solution

max amount of solute that can dissolve at a given temp

supersaturated solution

contains more solute than a saturated solution and is unstable

how does temp affect solubility of solids and gases

Solubility of solids increases, solubility of gases decreases

henrys law

the solubility of a gas in a liquid is directly proportional to the gas pressure above the liquid C=kP

colligative property

a property that depends on the number of solute particles not their identity

name four colligative properties

vapor pressure lowering, boiling point elevation, freezing point depression, osmotic pressure

molarity (M) equation

moles of solute/ liters of solution

molality (m) equation

moles of solute/ kg of solvent

mass percent equation

mass of solute/ mass of solution x 100

mole fraction (x) equation

moles of component/ total moles in solution

raoults law

vapor pressure of a solution equals the mole fraction of the solvent x vapor pressure of the pure solvent

Psolution​=Xsolvent​⋅Psolvent0​

why does adding solute lower vapor pressure

solute particles block surface area reducing solvent evaporation

why does boiling point increase in a solution

lower vapor pressure means more energy (higher temp) is needed to boil

boiling point elevation equation

ΔTb​=i⋅Kb​⋅m

freezing point depression equation

ΔTf​=i⋅Kf​⋅m

osmosis

the flow of solvent through a semi-permeable membrane from a lower to higher solute concentration

osmotic pressure equation

II=iMRT

reverse osmosis

applying pressure to force solvent out of a solution through a semi permeable membrane

how can colligative properties be used to find molar mass

Use ΔTf, ΔTb, or Π to find molality → moles → molar mass = mass/moles.

why do electrolytes have a greater effect on colligative properties

they produce more particles in solution due to ion dissociation

vant hoff factor (i)

number of particles into which a solute dissociates in solution

why is the measured vant hoff factor less than expected

ion paring occurs- some ions stick together reducing particle count

how do you calculate colligative effects for strong electrolytes

Use modified equations including i:

• ΔT=iKm

• Π=iMRT

how can colligative properties help determine the measured vant hoff factor

Compare experimental ΔTf, ΔTb, or Π to theoretical values; solve for i.