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Water and Aqueous Systems
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Water Molecule
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Hydrogen Bonds
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Properties of Water Resulting from Hydrogen Bonding
High surface tension Low vapor pressure High specific heat capacity High heat of vaporization High boiling point
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Surface Properties Surface tension: the inward pull or force the tends to minimize the surface area of a liquid Water molecules are only hydrogen bonded on one side and are not attracted to the air
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Water Droplets Surface tension holds liquids in a spherical shape- smallest surface area for a given volume Gravity flattens it The stronger the surface tension the more spherical the drop
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Surfactant Surface Acting Agent Decreases surface tension
Interferes with hydrogen bonding
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Specific Heat Capacity
Because of hydrogen bonding the specific heat of water is higher than that of most other substances
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Evaporation and Condensation
Evaporation kJ per gram is absorbed Condensation: 2.26 kJ per gram is released
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Melting Points and Boiling Points of Some Substances with Low Molar Mass
Name of Substance Formula Molar Mass (g/mol) Melting Point (oC) Boiling Point (oC) Methane CH4 16 -183 -164 Ammonia NH3 17 -77.7 -33.3 Water H2O 18 100 Neon Ne 20 -249 -246 Methanol CH3OH 32 -93.9 64.9 Hydrogen Sulfide H2S 34 -85.5 -60.7
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Boiling Points and Melting Points
Molecular compounds with low molar masses tend to have low boiling points Boling Point: oC Boiling Point: 100oC
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Hydrogen Bonding in Ice
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Ice Snowflake Symmetry is Due to Hydrogen Bonding
Ice is less dense than Water
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Solvents and Solutes Aqueous Solutions: Water samples containing dissolved substances Solute: the dissolved particles Solvent: The medium the particles dissolve in Solutions are homogeneous mixtures Solutes can be solids, liquids or gases- ionic or molecular
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Like Dissolves Like Solvation: the process that occurs when a solute dissolves H2O and NaCl H2O and Oil
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Electrolytes and Nonelctrolytes
Electrolytes: compounds that conduct electricity in aqueous solution or molten state ALL Ionic compounds are electrolytes Not all conduct to the same degree Nonelectrolytes: don’t conduct
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Water of Hydration The water in a crystal CuSO4*5H20
A compound that contains water of hydration is called a hydrate
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Water of Hydration Effloresce: if a hydrate has a higher vapor pressure than the water in the air the hydrate will lose water
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Water of Hydration Hygroscopic: remove water from the air
Desiccants: drying agents (remove water from the air)
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Water of Hydration Deliquescent: can remove enough water from the air to form a solution
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Suspensions Mixtures from which particles settle out upon standing
Bigger particles than in a solution Heterogeneous
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Colloids Heterogeneous mixtures containing particles in between a suspension and a solution
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Tyndall Effect Particles in a colloid scatter visible light in all directions Suspensions also exhibit Tyndall effect but solutions NEVER do
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Brownian Motion Particles in a colloid viewed under a microscope will flash (scintillate) because of Brownian motion- the chaotic motion of the particles Caused by the collisions between water molecules and colloidal particles
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Emulsions Colloidal dispersions of liquids in liquids
An emulsifying agent is necessary for the formation and maintenance of an emulsion
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