READING FOR TUESDAY: Chapter 12 sections 3 – 5 HOMEWORK – DUE THURSDAY 11/19/15
HW-BW 10.2 CH 10 #’s 72, 73, 75, 78, 79, 88, 93, 93 HW-BW 11 CH 11 #’s 1-12 (all), 16-24 (even), 25
HOMEWORK – DUE Tuesday 11/24/15 HW-WS 18 (Worksheet) (from course website)
Lab Wednesday/Thursday – EXP 14 continued
Exam 4 Next Tuesday
SolutionsSolution – A system in which one or more
substances are mixed or dissolved in another substance.
Solute – The substance that is being dissolved, or the least abundant component, of a solution.
Solvent – The dissolving agent or the most abundant component in a solution.
A solute goes into a solvent to make a solution(solute + solvent = solution)
Time to Concentrate! Solutions have variable composition The concentration of a solution tells us how much solute is
dissolved in a given quantity of solution. Many measurements for the concentration of a solution:
volume/volume percent
mass/mass percent
ppm (parts-per-million)
molarity
osmolarity
mole fraction
molality
mass of solute
100 = %mass of solution
volume of solute
100 = %volume of solution
mole of solute=
volume of solutionM
mole of solute=
mole of solution
mass of solute
1000000 = ppmmass of solution
mole of dissolved solute=
volume of solutionosM
mole of solute=
kg of solventm
Time to Concentrate!
Moles of solute per 1 kilogram of solventdefined in terms of amount of solvent, not solution
Does not vary with temperatureUsed mostly in freezing-point depression and
boiling-point elevation calculations
When molality is given, it is ALWAYS per 1 kg
Time to Concentrate on Molality, m!
mole of solute=
kg of solventm
Time to Concentrate on Molality, m!
mole of solute=
kg of solventm
What is the molality of a solution prepared by mixing 17.2 g of C2H6O2 with 475 g of H2O to make 480 mL of solution?
117.2 0.27706
62.08 2 6 2
2 6
6 22 6 2
2
2C H OC
C H OC H
H OO
mol mol g
g
3
1475 0.475
1 10
2
2
22
H OH OH O
H O
kg kg
g
g
0.27706
0.475
2
2 62
22 6H O
0.583 C H O
C H Omol
g
km
Colligative PropertiesColligative properties are properties whose value
depends only on the number of solute particles, and not on what they areValue of the property depends on concentration of the
solutionOsmotic pressure
Directly related to concentrationVapor pressure
Inversely related to concentrationBoiling point
Rises with added solute, change is directly related to concentrationFreezing point
Drops with added solute, change is directly related to concentration
Colligative Properties – Freezing Point The freezing point of a solution is always lower than the
freezing point of the pure solvent Hence freezing point DEPRESSION
The difference between the freezing point of the solution and freezing point of the pure solvent is directly proportional to the molality of solute particles
The proportionality constant is called the Freezing Point Depression Constant, Kf
Kf depends on the solvent
the units of Kf are °C/m
f fΔT K m iDTf = change from normal boiling point
Kf = solvent dependent constant
m = molality of solution
i = van’t Hoff factor
Colligative Properties – van’t Hoff Factor Ionic compounds produce multiple solute particles for each
formula unit The theoretical van’t Hoff factor, is the ratio of moles of
solute particles to moles of formula units dissolved NaCl makes 2 particles CaCl2 makes 3 particles
AlCl3 makes 4 particles
Al2(SO4)3 makes 5 particles
C6H12O6 makes 1 particle
The measured van’t Hoff factors are generally less than the theoretical due to ion pairing in solution so the measured van’t Hoff factor often causes the DT to be
smaller than expected
f fΔT K m i
Colligative Properties – van’t Hoff Factor
Colligative Properties – Freezing PointWhat is the freezing point of a salt water solution made from 25.00 grams of NaCl in 1.250 kg of water? (Kf,water = 1.86 °C/m)
f fΔT K m i
1.86 C fΔT m i
m
158.44
25.001.86
1.250
C
NaCl NaCl
f2
NaClΔT
H O
mol g
gi
m kg
158.44
25.001.86
1.250
C
NaCl NaCl
f2
NaClΔT
H O
mol g
molkg
gi
kg
158.44
25.001.86 2
1.250
C
NaCl NaCl
f2
NaClΔT
H O
mol g
molkg
g
kg
158.44
25.001.86 2
1.250
C
NaCl NaCl o
f2
NaCl
ΔT 1.27 C
H O
mol g
molkg
g
kg
FPsolution = FPwater – DTf
FPsolution = 0.00 oC – 1.27 oC
FPsolution = – 1.27 oC
Intermolecular Forces Intramolecular or bonding forces are found within a
molecule. The chemical behavior of each phase of matter is the same because the same constituent particle is present in each case. H2O molecules are present whether the substance is in the solid,
liquid, or gas phase. Intermolecular or nonbonding forces are found between
molecules. The physical behavior of each phase of matter is different because the strength of these forces differs from state to state.
Intermolecular forces are relatively weak compared to intramolecular forces because they involve smaller charges that are farther apart.
Intermolecular forces are the attractions BETWEEN separate particles!
Can be used to predict general trends in some physical properties.
The stronger the attractive forces are, the higher will be the boiling point of the liquid and the melting point of the solid Solids melt when heated because the particles gain enough kinetic
energy to partially overcome (loosen) the attractive forces Liquids boil when heated because the particles gain enough kinetic
energy to completely overcome (break) the attractive forces
Intermolecular Forces