chapter 17 water and aqueous systems liquid water and its properties water vapor and ice aqueous...
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Chapter 17Water and Aqueous Systems
• Liquid Water and Its Properties
• Water Vapor and Ice
• Aqueous Solutions
• Heterogeneous Systems
Ch 17.1 Liquid Water and Its Properties
• The Water Molecule
• Surface Properties
• Specific Heat Capacity
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
Properties due to Hydrogen Bonding
• High Surface Tension
• Low Vapor Pressure
• High Specific Heat Capacity
• High Heat of Vaporization
• High Boiling Point
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
Low Vapor Pressure
• Hydrogen Bonds hold water molecules together preventing them from entering the vapor phase
Water in Space
• http://video.google.com/videoplay?docid=-5089084492638545730
• http://video.google.com/videoplay?docid=243028165368764588&q=water+in+space&total=3270&start=0&num=10&so=0&type=search&plindex=9
• http://video.google.com/videoplay?docid=5098206590977878321&q=water+in+space&total=3270&start=10&num=10&so=0&type=search&plindex=1
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?
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?
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.
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?
Ch 17.3 Aqueous Solutions
• Solvents and Solutes
• The Solution Process
• Electrolytes and Nonelectrolytes
• Water of Hydration
Solution Process in Three Steps
• Step 1 – Separation of solvent molecules, requires energy to break intermolecular forces (ΔH1)
• Step 2 – Separation of solute molecules, requires energy to break intermolecular forces (ΔH2)
• Step 3 – Solvent and Solute Molecules Mix, may be exothermic or endothermic (ΔH3)
Heat of Solution ΔHsoln
• ΔHsoln = ΔH1 + ΔH2 + ΔH3
• ΔHsoln < 0 , exothermic, solution process is favorable
• ΔHsoln > 0 , endothermic, solution process is not favorable
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
Nonelectrolytes
• Compounds that do not conduct an electrical current in an aqueous solution of molten state
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
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
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
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
Tyndall Effect
• Scattering of visible light in all directions
• Suspensions can exhibit the Tyndall Effect, solutions never do
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
Emulsions
• Colloidal dispersions of liquids in liquids
• Example: Oil and water mixed together with soap
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