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Properties of Solutions

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Properties of Solutions Chapter 11 Composition of Solutions Solutions = homogeneous mixtures, any state of matter (mol solute*cation charge) L solution ... – PowerPoint PPT presentation

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Title: Properties of Solutions


1
Properties of Solutions
  • Chapter 11

2
Composition of Solutions
  • Solutions homogeneous mixtures,
    any state of matter

Solid
Gas
Liquid
Gas
Liquid
Solid
3
How to Calculate Concentration
Mole Fraction
Molarity
Molality
Mass Percent
Normality
(mol solutecation charge) L solution
4
Energies 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)

5
Enthalpy 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
6
Try Me!
  • Decide whether liquid hexane (C6H14) or liquid
    methanol (CH3OH) is more appropriate solvent for
    substances, grease (C20H42) and potassium iodide
    (KI).

7
Factors 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.

8
Colligative 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

9
Vapor 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.

10
François 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!
11
Try 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.

12
Answer
  • 23.431 torr

13
More 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.

14
Volatile 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.

15
Boiling 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

16
Freezing 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

17
Try 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.

18
Osmotic 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.

19
P 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

20
Colligative 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

21
Vant 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
22
Ion 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.

23
Colloids
  • Suspension of tiny particles in a medium caused
    by electrostatic repulsion.
  • Tyndall Effect Scattering of light effect by
    suspended particles.
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