Title: Properties of Solutions
1Properties of Solutions
2Composition of Solutions
- Solutions homogeneous mixtures,
any state of matter
Solid
Gas
Liquid
Gas
Liquid
Solid
3How to Calculate Concentration
Mole Fraction
Molarity
Molality
Mass Percent
Normality
(mol solutecation charge) L solution
4Energies of Solutions
- Like Dissolves Like
- Polar solvents dissolve polar solutes
- Non-Polar solvents dissolve non-polar solutes
- WHY?
- ENTHALPY OF SOLUTION
- 3 part process
- Solute components separate (endo)
- Overcome IMFs in solvent (endo)
- Solvent and Solute interact (exo)
5Enthalpy of Solution
- DHsoln DH1 DH2 DH3
- Heat of solution can either be or
- DH is expected to be small for non-polar
molecules except for when they are very large
molecules.
DHsoln is large and This rarely occurs
DHsoln is large and - This usually occurs
DHsoln is close to zero Exceptions,
because Spontaneity does not Depend solely on
enthalpy
6Try Me!
- Decide whether liquid hexane (C6H14) or liquid
methanol (CH3OH) is more appropriate solvent for
substances, grease (C20H42) and potassium iodide
(KI).
7Factors Affecting Solubility
- Structure---Polarity
- Non polar are hydrophobic
- Polar are hydrophillic
- Some are a combo with different ends.
- Vitamin C and scurvy
- Pressure---works only on gases
- C kP (Henrys Law)
- gas a Pvapor
- Temperature---not always a direct relationship
- Gas in water as T increases, solubility
decreases - See solubility curves for individual compound
reactions to temperature.
8Colligative Properties
- A property of a solution that depends only on the
number, and not on the identity of the solute
particles present. - Vapor Pressure
- Boiling Point Elevation
- Freezing Point Depression
- Osmotic Pressure
9Vapor Pressure
- Non-volatile Solute added to solvent
- Reduces the tendency of the solvent molecules to
escape (evaporate) - Equilibrium pressure of the solvent is higher
than equilibrium pressure of solution. More of
the solvent (pure) has to evaporate to be at
equilibrium than is the case in a beaker full of
solution.
10François Raoult and his Law
- Vapor pressure of a solution is directly
proportional to the mole fraction of the solvent
present.
Psoln XsolventPosolvent
Just what I was thinking!!
Me Too!
I agree!
11Try Me!
- Calculate the expected vapor pressure at 25oC for
a solution prepared by dissolving 85.58 g of
table sugar (sucrose molar mass 342.3 g/mol) in
320.5 cm3 of water. The vapor pressure of water
is 23.76 torr at this temperature.
12Answer
13More solute, lower vapor pressure
- Predict the vapor pressure of a solution prepared
by mixing 35.0 g solid Na2SO4 with 175 g water
at 25oC. The vapor pressure of water is still
23.76 torr.
14Volatile solutes
- Raoults Law is modified to account for the vapor
pressure of both solute. - Ptotal Pa Pb XaPao XbPbo
- Always some degree of deviation from idealmore
similar the solute is to the solvent the more
ideal it behaves.
15Boiling Point Elevation
- When a solute is added, vapor pressure is
lowered. - Must be heated to higher temperature to give
reach normal boiling point. - Boiling point is higher than usual.
- DT Kbmsolute
16Freezing Point Depression
- When a solute is added, the vapor pressure is
lowered. - Water in the solution has a lower vapor pressure
than that of pure ice. - Ice will not form.
- Freezing point has been lowered.
- DT Kfmsolute
17Try Me!
- A chemist is trying to identify a human hormone,
which controls metabolism by determining its
molar mass. A sample weighing 0.546 g was
dissolved in 15.0 g benzene, and the freezing
point depression was determined was determined to
be 0.240oC. Calculate the molar mass of the
hormone.
18Osmotic Pressure
- Solvent, but not solute can pass through a
semi-permeable membrane via osmosis. - When pure solvent and solution volumes are
stabilized (the system is at equilibrium) there
is a greater pressure on the solution side. - The difference in pressure is the Osmotic
Pressure.
19P MRT
- Used to determine osmotic pressure.
- P is osmotic pressure
- M is molarity of solution
- R is the gas law constant (0.0821 Latm/Kmol)
- T is the temperature in Kelvin
20Colligative Properties of Electrolyte Solutions
- The type of solute DOES matter sometimes
- Only in ability to dissociate
- Compare 0.1 m glucose to 0.1m NaCl
21Vant Hoff Factor
- Vant Hoff Factor expresses the relationship
between moles of solute and solution - This is a multiplier number that describes the
ratio of elevation or depression. -
i moles particles moles solute
DT iKbm
DT iKfm
P iMRT
22Ion Pairing
- Vant Hoff factor is fallible.
- Ion Pairing at a certain instant, some ions may
not be dissociated, and thus count as a single
particle. - Still use equations, but keep in mind that there
can be some deviation.
23Colloids
- Suspension of tiny particles in a medium caused
by electrostatic repulsion. - Tyndall Effect Scattering of light effect by
suspended particles.