Title: Solutions and Mixtures
1Solutions and Mixtures
2Solutions
- Solutions are stable, homogeneous mixtures
- Particles are evenly distributed through the
mixture - Will not spontaneously separate
- There are two parts solute and solvent
3Parts of a Solution
- Solute the substance being dissolved
- Solvent the substance doing the dissolving
(think water universal solvent)
4Classes of Solutions
- Classes are based on the final state of matter of
the soln - Three classes
- Gaseous solns mixtures of two gases
- Liquid solns gas, liquid, or solid is
dissolved in a liquid - Solid solns solid and a liquid or two solids
are melted, mixed, or cooled - Alloys solid solutions containing metals
5Solution of a gas (hydrogen) in a solid
(palladium)
6Examples of solid solutions
7Solution Terms
- Most solns are combinations of liquids and
solids - Miscible liquids or gases that will dissolve in
each other - Immiscible liquids or gases that will not
dissolve in each other - Soluble able to be dissolved in a particular
solvent - Insoluble not able to be dissolved in a
particular solvent
8Concentrations
- Concentrated solution a large amount of solute
is dissolved in the solvent - Dilute solution a small amount of solute is
dissolved in the solvent
9Saturation
- Saturated soln a soln that has dissolved all
the solute it can hold at a given temp - NOT the same as concentrated
- Soln can be saturated but not concentrated and
vise versa
10Saturation (cont)
- Unsaturated soln any soln that can dissolve
more solute at a given temp - Supersaturated soln soln that contains more
solute than a saturated one has at that temp - It is unstable
- Crystallization from Supersaturated Solutions of
Sodium Acetate
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12Determining Saturation
- Add a solute crystal to a soln
- If dissolves unsaturated
- If does not dissolve saturated
- If excess solute comes out supersaturated
13The Formation of Solns
- The process of dissolving takes place at the
surface of the solid solute - Water molecules orient themselves on the surface
of the crystal so that they can separate the
pieces and pull them into soln - Once separated, the pieces are surrounded by
water molecules
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15Formation of Soln (cont)
- Solvation process of surrounding solute
particles with solvent particles - Hydration solvation involving water
- Formation of a soln involves
- Breaking the attractions among solute particles
- Breaking the attractions among solvent particles
- Formation of attractions between solute and
solvent particles
16Heat of Solution
- Defined as overall energy change that occurs
during solution formation - Energy is required for formation of solns
- Breaking attractions endothermic
- Forming attractions exothermic
- Overall process (net change) depends on the
balance between breaking and forming attractions - If breaking requires more energy endothermic
- If forming releases more energy - exothermic
17Solubility
- Defined as the maximum amount of a solute that
will dissolve in a given amount of solvent at a
specific temp - Determined experimentally
- Usually expressed in grams of solute per 100
grams of solvent at a specific temp and pressure
18Solubility
- Based on the idea of attractions between
particles - Overall polarity determines solubility
- Like dissolves like
- Polar dissolves polar
- Nonpolar dissolves nonpolar
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20Picture of a soap micelle.
21Solvation
- The extent to which one substance dissolves in
another depends on - State of solute and solvent
- Temp and pressure
- Solubilities change with temp (the key to
preparing a supersaturated soln) - Solubility of solids and liquids increases
- Solubility of gases in liquids decreases
22Solubilities of Substances in Water
23Solubilities of Gases in Water
24Henrys Law
- Solubilities of solids and liquids are not
appreciably affected by pressure, but solubility
of a gas in a liquid is strongly influenced by
pressure - Henrys Law the amount of gas dissolved in a
solvent is proportional to the partial pressure
of that gas over the solvent
25The solubility of a gas depends upon its partial
pressure above the solution.
26Factors that Affect Rate of Solvation
- Must increase the collisions between solute and
solvent particles to increase rate at which
solute dissolves. - Three ways
- Agitate mixture (stir, shake)
- Increase surface area (breaking solute into small
pieces) - Increase temp of solvent
27- Because dissolving occurs at the surface,
stirring/shaking allows more solvent to come in
contact with solute - Increasing surface area does the same thing
- As temp increases, solvent particles move faster,
which causes more particles to come in contact
with the solute. - Particles of solvent have more energy to remove
particles from the solid solute
28Aqueous Solutions
- Ionic compounds dissociate in water
- Dissociate a process using energy to separate a
compound into ions in water - Molecular compounds may also dissociate in water
- Some aqueous solutions conduct electricity
29Aqueous Solns
- Conductance the measurement of a solns
ability to conduct electrical energy - Electrolyte any substance that will conduct an
electric current (by means of movement of ions),
when dissolved in soln - Nonelectrolyte any substance that will not
conduct an electric current when dissolved in
water
30Ways to Describe Solutions
- There are three ways to describe concentrations
- Molarity
- Molality
- Mole fraction
31Molarity
- Molarity (M) of moles of solute dissolved in
each liter of soln - M moles of solute
- liters of soln
- Four different labels molarity, molar, M, or
mol/L - Dependent on temp
- Volumetric flasks are the best containers for
making a soln of a precise molarity
32- What is the molarity of a soln prepared by
dissolving 16.0 g of barium chloride in enough
water to give 450 mL of soln?
33- How many grams of potassium chloride are needed
to prepare 0.750L of a 1.50M soln of potassium
chloride?
34Molality
- Molality (m) of moles dissolved in each
kilogram of solvent - m moles of solute
- kg of solvent
- Independent of temp
35- Calculate the molality of a soln prepared by
dissolving 20.4 g of sodium chloride in 192g of
water.
36- What is the molality of a solid soln containing
0.125g of chromium and 81.3g of iron?
37Mole Fraction
- Mole fraction (X) of moles of one component
divided by the total of moles in the soln - X moles of component
- total moles of soln
- Used to compare solute and solvent
38- What are the mole fractions of ethyl alcohol
(C2H5OH) and water in a soln prepared by adding
50.0g of ethyl alcohol to 50.0g of water?
39- A gas mixture contains the following gases with
the mole fractions indicated CH4 (0.510), C2H6
(0.431), C3H8 (0.011), and C4H10 (0.013). The
mixture also contains the gas acetylene (C2H2).
What is the mole fraction of acetylene?
40Colligative Properties
- A physical property that is dependent on the of
particles present rather than on the size, mass,
or characteristics of those particles - Four main properties
- Vapor pressure reduction
- Boiling point elevation
- Freezing point depression
- Osmotic pressure
41Vapor Pressure Reduction
- Vapor pressure of a solvent containing a
nonvolatile solute is lower than the vapor
pressure of the pure solvent - Volatile means tending to evaporate readily
- Vapor pressure reduction is proportional to
concentration
42When a solute is added to the solvent, some of
the solute molecules occupy the space near the
surface of the liquid, as shown in the figure to
the left. When a solute is dissolved in a
solvent, the number of solvent molecules near the
surface decreases, and the vapor pressure of the
solvent decreases.
43Boiling Point Elevation
- Because vapor pressure is lower, a higher temp
will be needed to make the soln boil - The amount by which the boiling point is raised
is the boiling point elevation (?Tb) - It is directly proportional to the solns
molarity
44A close-up plot of vapor pressure versus
temperature for pure water (red curve) and for a
1.0 M NaCl solution (green curve). Pure water
boils at 100.0C, but the solution does not boil
until 101.0C.
45Freezing Point Depression
- The presence of solute molecules will lower the
freezing point of a substance - The more solute particles in soln, the greater
the lowering of the freezing pt - Freezing pt depression the ability of a
dissolved solute to lower the freezing point of
its soln - Why does salt melt ice?
46Osmotic Pressure
- When a semipermeable membrane is placed between 2
solns so that only solvent particles can move
through it, a net flow of solvent molecules will
occur from the less concentrated soln to the
more concentrated soln (osmosis) - Osmotic pressure the pressure required to
prevent osmosis - If 2 different solns have identical osmotic
pressure, no osmosis will occur (isotonic)
47A solution inside the bulb is separated from pure
solvent in the container by a semipermeable
membrane. Net passage of solvent from the
container through the membrane occurs, and the
liquid in the tube rises until an equilibrium is
reached. At equilibrium, the osmotic pressure
exerted by the column of liquid in the tube is
sufficient to prevent further net passage of
solvent.
48Heterogeneous Mixtures
- Suspension mixture that appears to be uniform
while being stirred, but separates into different
phases when agitation ceases - Colloid heterogeneous mixture that contains
intermediate size particles evenly distributed
through a dispersion medium
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50Heterogeneous Mixtures
- Brownian Motion jerky, erratic movement of
dispersed particles - Prevent colloids from settling out
- What is Brownian Motion?
- Tyndall effect scattering of light by dispersed
particles
51The light beam is not visible as it passes
through a true solution (right), but it is
readily visible as it passes through colloidal
silver in water.
52Tyndall effect in clouds.