Unit 6

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Unit 6 Solids, Liquids and Solutions
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Intermolecular Forces
Forces of attraction between different molecules
rather than bonding forces within the same
molecule.

• Dipole-dipole attraction
• Hydrogen bonds
• Dispersion forces

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Forces and Phases

• Substances with very little intermolecular
  attraction exist as gases
• Substances with strong intermolecular attraction
  exist as liquids
• Substances with very strong intermolecular (or
  ionic) attraction exist as solids

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Phase Differences
Solid definite volume and shape particles
packed in fixed positions particles are not free
to move
Liquid definite volume but indefinite shape
particles close together but not in fixed
positions particles are free to move
Gas neither definite volume nor definite shape
particles are at great distances from one
another particles are free to move
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Three Phases of Matter
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Effect of Pressure on Boiling Point
Boiling Point of Water at Various Locations Boiling Point of Water at Various Locations Boiling Point of Water at Various Locations Boiling Point of Water at Various Locations
Location Feet above sea level Patm (kPa) Boiling Point (?C)
Top of Mt. Everest, Tibet 29,028 32 70
Top of Mt. Denali, Alaska 20,320 45.3 79
Top of Mt. Whitney, California 14,494 57.3 85
Leadville, Colorado 10,150 68 89
Top of Mt. Washington, N.H. 6,293 78.6 93
Boulder, Colorado 5,430 81.3 94
Madison, Wisconsin 900 97.3 99
New York City, New York 10 101.3 100
Death Valley, California -282 102.6 100.3
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Types of Solids

• Crystalline Solids highly regular arrangement
  of their components table salt (NaCl), pyrite
  (FeS2).

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Representation of Components in a Crystalline
Solid

• Lattice A 3-dimensional system of points
  designating the centers of components (atoms,
  ions, or molecules) that make up the substance.

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Unit Cell
The smallest portion of a crystal lattice that
shows the three-dimensional pattern of the entire
lattice

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Packing in Metals

• Model Packing uniform, hard spheres to best use
  available space. This is called closest packing.
  Each atom has 12 nearest neighbors.

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Types of Solids

• Amorphous solids considerable disorder in their
  structures (glass and plastic).

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Water phase changes
constant
Temperature remains __________ during a phase
change.
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Phase Diagram

• Represents phases as a function of temperature
  and pressure.
• Critical temperature temperature above which
  the vapor can not be liquefied.
• Critical pressure pressure required to liquefy
  AT the critical temperature.
• Critical point critical temperature and
  pressure (for water, Tc 374C and 218 atm).

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Phase changes by Name
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Water
Water
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Carbon dioxide
Carbon dioxide
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Carbon
Carbon
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Sulfur
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Classification of Matter
Solutions are homogeneous mixtures
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Solute
A solute is the dissolved substance in a solution.
Salt in salt water
Sugar in soda drinks
Carbon dioxide in soda drinks
Solvent
A solvent is the dissolving medium in a solution.
Water in salt water
Water in soda
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Solvents
Solvents at the hardware store
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Dissolution of sodium Chloride
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Concentrated vs. Dilute
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Heat of Solution
The Heat of Solution is the amount of heat energy
absorbed (endothermic) or released (exothermic)
when a specific amount of solute dissolves in a
solvent.
Substance Heat of Solution (kJ/mol)
NaOH -44.51
NH4NO3 25.69
KNO3 34.89
HCl -74.84
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Electrolytes vs. Nonelectrolytes
The ammeter measures the flow of electrons
(current) through the circuit.

• If the ammeter measures a current, and the bulb
• glows, then the solution conducts.

• If the ammeter fails to measure a current, and
  the
• bulb does not glow, the solution is
  non-conducting.

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Definition of Electrolytes and Nonelectrolytes
An electrolyte is

• A substance whose aqueous solution conducts
• an electric current.

A nonelectrolyte is

• A substance whose aqueous solution does not
• conduct an electric current.

Try to classify the following substances as
electrolytes or nonelectrolytes
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Electrolytes?

1. Pure water
2. Tap water
3. Sugar solution
4. Sodium chloride solution
5. Hydrochloric acid solution
6. Lactic acid solution
7. Ethyl alcohol solution
8. Pure sodium chloride

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Answers to Electrolytes
ELECTROLYTES
NONELECTROLYTES

• Tap water (weak)
• NaCl solution
• HCl solution
• Lactate solution (weak)

• Pure water
• Sugar solution
• Ethanol solution
• Pure NaCl

But why do some compounds conduct electricity
in solution while others do not?
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Suspensions and Colloids
Suspensions and colloids are NOT solutions.
Suspensions The particles are so large that they
settle out of the solvent if not constantly
stirred.
Colloids The particle is intermediate in size
between those of a suspension and those of a
solution.
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Types of Colloids
Examples Dispersing Medium Dispersed Substance Colloid Type
Fog, aerosol sprays Gas Liquid Aerosol
Smoke, airborne bacteria Gas Solid Aerosol
Whipped cream, soap suds Liquid Gas Foam
Milk, mayonnaise Liquid Liquid Emulsion
Paint, clays, gelatin Liquid Solid Sol
Marshmallow, Styrofoam Solid Gas Solid foam
Butter, cheese Solid Liquid Solid emulsion
Ruby glass Solid Solid Solid sol
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The Tyndall Effect
Colloids scatter light, making a beam visible.
Solutions do not scatter light.
Which glass contains a colloid?
colloid
solution
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Factors Effecting Solubility

• The solubility of MOST solids increases with
  temperature.
• The rate at which solids dissolve increases with
  increasing surface area of the solid.
• The solubility of gases decreases with increases
  in temperature.
• The solubility of gases increases with the
  pressure above the solution.

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Therefore
Solids tend to dissolve best when

• Heated
• Stirred
• Ground into small particles

Liquids tend to dissolve best when

• The solution is cold
• Pressure is high

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Saturation of Solutions

• A solution that contains the maximum amount of
  solute that may be dissolved under existing
  conditions is saturated.
• A solution that contains less solute than a
  saturated solution under existing conditions is
  unsaturated.
• A solution that contains more dissolved solute
  than a saturated solution under the same
  conditions is supersaturated.

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Solubility Chart
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Calculations of Solution Concentration

• Concentration - A measure of the amount of
• solute in a given amount of solvent or solution

Grams per liter - the mass of solute divided by
the volume of solution, in liters
Molarity - moles of solute divided by the volume
of solution in liters
Parts per million the ratio of parts (mass) of
solute to one million parts (mass) of solution
Percent composition - the ratio of one part of
solute to one hundred parts of solution,
expressed as a percent
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Colligative Properties
Colligative properties are those that depend on
the concentration of particles in a solution, not
upon the identity of those properties.

• Boiling Point Elevation
• Freezing Point Depression
• Osmotic Pressure

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Freezing Point Depression
Each mole of solute particles lowers the freezing
point of 1 kilogram of water by 1.86 degrees
Celsius.
Kf 1.86 ?C ? kilogram/mol
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Boiling Point Elevation
Each mole of nonvolatile solute particles raises
the boiling point of 1 kilogram of water by 0.51
degrees Celsius.
Kb 0.51 ?C ? kilogram/mol
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Freezing Point Depression and Boiling Point
Elevation Constants
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Properties of Acids

• Acids taste sour
• Acids effect indicators
• Blue litmus turns red
• Methyl orange turns red
• Acids have a pH lower than 7
• Acids are proton (hydrogen ion, H) donors
• Acids react with active metals, produce H2
• Acids react with carbonates
• Acids neutralize bases

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Acids you SHOULD know
Strong Acids
Weak Acids
Sulfuric acid, H2SO4
Phosphoric acid, H3PO4
Hydrochloric acid, HCl
Acetic acid, HC2H3O2
Nitric acid, HNO3
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Sulfuric Acid

• Highest volume production of any chemical in the
  U.S.
• Used in the production of paper
• Used in production of fertilizers
• Used in petroleum refining

Thick clouds of sulfuric acid are a feature of
the atmosphere of Venus. (image provided by NASA)
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Nitric Acid

• Used in the production of fertilizers
• Used in the production of explosives
• Nitric acid is a volatile acid its reactive
  components evaporate easily
• Stains proteins (including skin!)

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Hydrochloric Acid

• Used in the pickling of steel
• Used to purify magnesium from sea water
• Part of gastric juice, it aids in the digestion
  of protein
• Sold commercially as Muriatic acid

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Phosphoric Acid

• A flavoring agent in sodas
• Used in the manufacture of detergents
• Used in the manufacture of fertilizers
• Not a common laboratory reagent

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Acetic Acid

• Used in the manufacture of plastics
• Used in making pharmaceuticals
• Acetic acid is the acid present in vinegar

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Acids are Proton Donors
Monoprotic acids
Diprotic acids
Triprotic acids
H3PO4
HCl
H2SO4
HC2H3O2
H2CO3
HNO3
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Strong Acids vs. Weak Acids
Strong acids are assumed to be 100 ionized in
solution (good proton donors).
HCl
H2SO4
HNO3
Weak acids are usually less than 5 ionized in
solution (poor proton donors).
H3PO4
HC2H3O2
Organic acids
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Strong Acid Dissociation
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Weak Acid Dissociation
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Organic Acids
Organic acids all contain the carboxyl group,
sometimes several of them.
The carboxyl group is a poor proton donor, so ALL
organic acids are weak acids.
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Examples of Organic Acids

• Citric acid in citrus fruit
• Malic acid in sour apples
• Deoxyribonucleic acid, DNA
• Amino acids, the building blocks of protein
• Lactic acid in sour milk and sore muscles
• Butyric acid in rancid butter

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Acids Effect Indicators
Blue litmus paper turns red in contact with an
acid.
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Acids Have a pH less than 7
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Acids React with Active Metals
Acids react with active metals to form salts and
hydrogen gas.
Mg 2HCl ? MgCl2 H2(g)
Zn 2HCl ? ZnCl2 H2(g)
Mg H2SO4 ? MgSO4 H2(g)
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Acids React with Carbonates
2HC2H3O2 Na2CO3
2 NaC2H3O2 H2O CO2
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Effects of Acid Rain on Marble(calcium carbonate)
George Washington BEFORE
George Washington AFTER
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Acids Neutralize Bases
Neutralization reactions ALWAYS produce a salt
and water.
HCl NaOH ? NaCl H2O
H2SO4 2NaOH ? Na2SO4 2H2O
2HNO3 Mg(OH)2 ? Mg(NO3)2 2H2O
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Properties of Bases

• Bases taste bitter
• Bases effect indicators
• Red litmus turns blue
• Phenolphthalein turns purple
• Bases have a pH greater than 7
• Bases are proton (hydrogen ion, H) acceptors
• Solutions of bases feel slippery
• Bases neutralize acids

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Examples of Bases

• Sodium hydroxide (lye), NaOH
• Potassium hydroxide, KOH
• Magnesium hydroxide, Mg(OH)2
• Calcium hydroxide (lime), Ca(OH)2

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Bases Effect Indicators
Red litmus paper turns blue in contact with a
base.
Phenolphthalein turns purple in a base.
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Bases have a pH greater than 7
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Bases Neutralize Acids
Milk of Magnesia contains magnesium hydroxide,
Mg(OH)2, which neutralizes stomach acid, HCl.
2 HCl Mg(OH)2
MgCl2 2 H2O