Chapter 17 Water and Aqueous Systems

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Chapter 17Water and Aqueous Systems

• Liquid Water and Its Properties
• Water Vapor and Ice
• Aqueous Solutions
• Heterogeneous Systems

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Water

• Make a list of everything you know about water

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Why is this going to hurt?
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Ch 17.1 Liquid Water and Its Properties

• The Water Molecule
• Surface Properties
• Specific Heat Capacity

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The Water Molecule

• H2O
• Triatomic
• O-H Polar Covalent Bond
• Oxygen highly electronegative, therefore acquires
  the slightly negative charge
• Bond Angle of 105o
• Dipole forces of attraction

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Properties due to Hydrogen Bonding

• High Surface Tension
• Low Vapor Pressure
• High Specific Heat Capacity
• High Heat of Vaporization
• High Boiling Point

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Surface Tension

• Molecules in a liquid are pulled in all
  directions due to intermolecular forces
• The molecules at the top are only pulled down and
  to the sides, they are not pulled up.
• These molecules tend to tighten up the top

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Surfactant

• A wetting agent that decreases surface tension of
  water, soap

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Low Vapor Pressure

• Hydrogen Bonds hold water molecules together
  preventing them from entering the vapor phase

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Specific Heat Capacity

• 4.18J (1 cal) to raise 1g of water 1oC
• High due to hydrogen bonding

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Water in Space

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Chapter 17.2 Water Vapor and Ice

• Evaporation and Condensation
• Ice

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Evaporation

• Heat of Vaporization - 2.26kJ of energy is needed
  to convert 1g of water at 100oC to 1g of steam at
  100oC (on your reference table)
• How much energy in kJ is required to change 52.3g
  of water at 100oC to steam at 100oC?

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Condensation

• 2.26kJ is given off when 1g of steam at 100oC is
  converted to 1g of water at 100oC
• How much energy in kJ is given off to change
  12.4g of steam at 100oC to water at 100oC?

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Ice

• As water cools it behave like most liquids and
  its density increases.
• Once it cools to 4oC, it decreases in density.
• Ice has about a 10 greater volume than water.
• Ice has a lower density than water, therefore it
  floats.

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Why does ice float?
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Heat of Fusion

• 334J of energy is needed to convert 1g of ice at
  0oC to 1g of water at 0oC (on your reference
  table)
• How much energy in kJ is required to change 21.8g
  of ice at 0oC to water at 0oC?

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Ch 17.3 Aqueous Solutions

• Solvents and Solutes
• The Solution Process
• Electrolytes and Nonelectrolytes
• Water of Hydration

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Aqueous Solutions

• Water with dissolved samples in it

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Solvents

• The dissolving medium

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Solutes

• The dissolved particles

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Name the Solvent and Solute

• Kool Aid

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Name the Solvent and Solute

• Hot Chocolate

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Name the Solvent and Solute

• Salt Water

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Name the Solvent and Solute

• Tea

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Solution Process in Three Steps

• Step 1 Separation of solvent molecules,
  requires energy to break intermolecular forces
  (?H1)
• Step 2 Separation of solute molecules, requires
  energy to break intermolecular forces (?H2)
• Step 3 Solvent and Solute Molecules Mix, may be
  exothermic or endothermic (?H3)

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Heat of Solution ?Hsoln

• ?Hsoln ?H1 ?H2 ?H3
• ?Hsoln lt 0 , exothermic, solution process is
  favorable
• ?Hsoln gt 0 , endothermic, solution process is not
  favorable

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Electrolytes

• Compounds that conduct an electrical current in
  an aqueous solution or molten state
• All ionic compounds are electrolytes
• Barium sulfate conducts electricity in the molten
  state but not in the aqueous state, WHY?
• Insoluble in water

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Nonelectrolytes

• Compounds that do not conduct an electrical
  current in an aqueous solution of molten state

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Weak Electrolytes

• When in solution, only a fraction of the solute
  exists as ions

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Strong Electrolytes

• When in solution, most of the solute exists as
  ions

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Strong Electrolytes Weak Electrolytes Non-Electrolytes
ACIDS(Inorganic) HCl HBr HI HNO3 H2SO4 HClO4 BASES(Inorganic) NaOH KOH Soluble Salts KCl MgSO4 KClO3 Heavy Metal Halides HgCl2 PbCl2 Bases(Inorganic) NH3 Acids (Organic) Acetic Acid Bases (Organic) aniline H2O Most Organic Compounds Glucose Glycerol
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Water of Hydration (Crystallization)

• The water molecules that make up part of a
  crystal
• A compound that contains water of hydration is
  called a hydrate

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Copper(II) Sulfate Pentahydrate Deep Blue
Crystals
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Ch 17.4 HeterogeneousAqueous Systems

• Suspensions
• Colloids

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Suspensions

• Mixtures from which particles settle out upon
  standing
• The particles are much larger than that of a
  solution
• Heterogeneous
• Particles larger than 100nm
• Can be filtered

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Colloid

• Heterogeneous mixtures containing particles that
  are intermediate in size between suspensions and
  solutions
• Size between 1nm and 100nm
• Glue, Jell-O, paint, smoke
• Cloudy or milky in appearance when concentrated
• Clear or almost clear when they are dilute

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Tyndall Effect

• Scattering of visible light in all directions
• Suspensions can exhibit the Tyndall Effect,
  solutions never do

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Brownian Motion

• Chaotic movement of colloidal particles
• Caused by collisions between water particles and
  small dispersed colloidal particles
• These collisions prevent the particles from
  settling

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Emulsions

• Colloidal dispersions of liquids in liquids
• Example Oil and water mixed together with soap

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