Water and Aqueous Systems
Water Molecule
Hydrogen Bonds
Properties of Water Resulting from Hydrogen Bonding High surface tension Low vapor pressure High specific heat capacity High heat of vaporization High boiling point
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
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
Surfactant Surface Acting Agent Decreases surface tension Interferes with hydrogen bonding
Specific Heat Capacity Because of hydrogen bonding the specific heat of water is higher than that of most other substances
Evaporation and Condensation Evaporation 2.26 kJ per gram is absorbed Condensation: 2.26 kJ per gram is released
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
Boiling Points and Melting Points Molecular compounds with low molar masses tend to have low boiling points Boling Point: -33.3 oC Boiling Point: 100oC
Hydrogen Bonding in Ice
Ice Snowflake Symmetry is Due to Hydrogen Bonding Ice is less dense than Water
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
Like Dissolves Like Solvation: the process that occurs when a solute dissolves H2O and NaCl H2O and Oil
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
Water of Hydration The water in a crystal CuSO4*5H20 A compound that contains water of hydration is called a hydrate
Water of Hydration Effloresce: if a hydrate has a higher vapor pressure than the water in the air the hydrate will lose water
Water of Hydration Hygroscopic: remove water from the air Desiccants: drying agents (remove water from the air)
Water of Hydration Deliquescent: can remove enough water from the air to form a solution
Suspensions Mixtures from which particles settle out upon standing Bigger particles than in a solution Heterogeneous
Colloids Heterogeneous mixtures containing particles in between a suspension and a solution
Tyndall Effect Particles in a colloid scatter visible light in all directions Suspensions also exhibit Tyndall effect but solutions NEVER do
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
Emulsions Colloidal dispersions of liquids in liquids An emulsifying agent is necessary for the formation and maintenance of an emulsion