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Solutions

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Title: Solutions


1
Solutions
  • Chapter 13 and 14
  • Honors Chemistry

2
Solution
  • Definition a homogeneous mixture of 2 or more
    substances in a single physical state
  • Parts solute and solvent (usually water)

3
Types of solutions
  • Physical states solid (alloys), liquid, gas
  • Miscible vs. Immiscible
  • Miscible - liquids that dissolve freely in one
    another in any proportion
  • Immiscible - liquid solutes and solvents that are
    not soluble
  • Dilute vs. Concentrated
  • Electrolyte vs. Nonelectrolyte
  • Saturated, Unsaturated and Supersaturated

4
Supersaturated Solution demo
5
Electrolyte vs. Nonelectrolyte
6
  • Saturated soln containing the max amt of solute
  • Unsaturated soln containing less solute than a
    sat soln under the existing conditions
  • Supersaturated contains more dissolved solute
    than a saturated solution under the same
    conditions

Solubility Curves
7
supersaturated solution(stirred)
8
Solubility (physical change)
  • Definition mass of solute needed to make a
    saturated solution at a given temperature
  • solution equilibrium in a closed system
  • dissolution ? crystallization
  • Unit g solute/100 g H2O

9
At 20oC, a saturated solution contains how many
grams of NaNO3 in 100 g of water?
Saturated soln
90 g
What is the solubility at 70oC?
Supersaturated solution
135 g/100 g water
What kind of solution is formed when 90 g NaNO3
is dissolved in 100 g water at 30oC?
Unsaturated solution
unsaturated
What kind of solution is formed when 120 g NaNO3
is dissolved in 100 g water at 40oC?
supersaturated
10
Solubility of solids in liquids
  • For most solids, increasing temperature,
    increases solubility.
  • In general, like dissolves like. Depends on
  • Type of bonding
  • Polarity of molecule
  • Intermolecular forces between solute and solvent

11
Solubility of Gases
  • Gases are less soluble at high temperatures than
    at low temperatures
  • Increasing temperature, decreases solubility.
  • Increasing pressure, increases solubility.

12
  • The quantity of gas that dissolves in a certain
    volume of liquid is directly proportional to the
    pressure of the gas (above the solution).

13
  • Effervescence rapid escape of gas dissolved in
    liquid

14
Factors Affecting Solubility
  • Increase surface area of solute (crushing)
  • Stir/shake
  • Increase temperature

15
Dissolution Process
  • Ionic Compounds
  • NaCl(s) ? Na1(aq) Cl-1(aq)
  • For dissolution to occur, must overcome solute
    attractions and solvent attractions.
  • Dissociation Reaction the separation of IONS
    when an ionic compound dissolves (ions already
    present)
  • Try calcium chloride

electrolyte
nonelectrolyte
Dissolving NaCl in water
hexahydrated for Na1 most cations have 4-9 H2O
molecules 6 is most common
Solvation process of solvent molecules surroundin
g solute Hydration solvation with water
16
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17
Dissolution Process
  • Molecular Compounds
  • Nonpolar molecular solids do not dissolve in
    polar solvents
  • naphthalene
  • Polar molecule
  • C12H22O11(s) ? C12H22O11(aq)
  • Molecular solvation
  • Nonelectrolyte
  • Polar molecule
  • HCl(g) ? H1(aq) Cl-1(aq) or
  • HCl(g) H2O ? H3O1(aq) Cl-1(aq)
  • Ionization ions formed from solute molecules by
    action of solvent (no ions initially present)
  • Nonelectrolyte (HCl) ? electrolyte (ions)

18
Energy Changes
  • Heat of solution ?Hsoln
  • Endothermic
  • Solute particles separating in solid
  • Solvent particles moving apart to allow solute to
    enter liquid
  • Energy absorbed
  • Exothermic
  • Solute particles separating in solid
  • Solvent particles attracted to solvating solute
    particles
  • Energy released

?Hsoln heat of solvation crystal lattice
energy
19
Solution Reactions
  • Single replacement
  • Activity Series
  • Double replacement
  • Solubility chart (soluble vs. insoluble)
  • Neutralization (water)
  • Gases (CO2 and H2S)

20
Concentration
  • Percent concentration by mass (mass )
  • (solute/solution) x 100 Concentration
  • Molarity (M)
  • Moles of solute/Liters of solution mol/L
  • Molality (m)
  • Moles of solute/mass of solvent mol/kg
  • ppm and ppb
  • Used for very dilute solutions
  • Dilution a process in which more solvent is
    added to a solution
  • How is this solution different?
  • Volume, color, molarity
  • How is it the same?
  • Same mass of solute, same moles of solute
  • In Dilution ONLY M1V1 M2V2

21
Colligative Properties
  • Definition physical properties of solutions
    that differ from properties of its solvent.
  • Property depends upon the number of solute
    particles in solution.
  • Types
  • Vapor Pressure
  • Boiling Point ELEVATION
  • Freezing Point DEPRESSION

22
Vapor PressureA measure of the tendency of
molecules to escape from a liquid
  • For nonvolatile liquids or solid solutes
  • A nonvolatile solute will typically increase the
    boiling point and decrease the freezing point.
  • Adding a nonvolatile solute lowers the
    concentration of water molecules at the surface
    of the liquid.
  • This lowers the tendency of the water molecules
    to leave the solution and enter the gas phase.
  • Therefore the vapor pressure of the solution is
    LESS than pure water.

23
Same Temperature
24
Boiling Point Elevation
  • ?tb boiling point elevation
  • ?tb iKbm
  • i molality conversion factor for electrolytes
    adjust for of ions actually present in solution
    (dissociation process)
  • Kb molal bp elevation constant
  • Kb 0.512C?kg H2O
  • moles of solute (ions or molecules)
  • m molality moles solute
  • kg of solvent
  • bp of solution bp of solvent ?tb

25
Boiling Point Elevation and Freezing Point
Problems
  • At what temperature will a solution begin to boil
    if it is composed of 1.50 g potassium nitrate in
    35.0 g of water?
  • Solute
  • At what temperature will a solution begin to
    freeze when 18.0 g ammonium phosphate is
    dissolved in 200.0 g water?
  • Solute

26
Freezing Point Depressionwhen a solution
freezes, the solvent solidifies as a pure
substance deviates for more concentrated
solutions
  • ?tf freezing point depression
  • ?tf iKfm
  • i molality conversion factor for electrolytes
    adjust for of ions actually present in solution
    (dissociation process)
  • Kf molal freezing point depression constant
  • Kf 1.858C?kg H2O
  • moles of solute (ions or molecules)
  • m molality moles solute
  • kg of solvent
  • fp of solution fp of solvent - ?tf

27
Osmotic Pressure
  • The external pressure needed to stop osmosis
  • Osmosis is the movement of solvent through a semi
    permeable membrane from lower concentration to
    higher concentration

28
the pressure required to allow for no transport
of solvent across the membrane is called the
OSMOTIC pressure
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