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