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Water and Aqueous Systems. Part I. Water Molecule . Triatomic (3 atoms) Bent Shape (104.45°) Polar Molecule. δ -. δ +. δ +. δ -. δ +. δ +. δ +. δ +. δ +. Important Water Properties resulting from hydrogen bonding. high surface tension low vapor pressure. Surface Properties.

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water molecule
Water Molecule
  • Triatomic (3 atoms)
  • Bent Shape (104.45°)
  • Polar Molecule

δ-

δ+

δ+

slide3

δ-

δ+

δ+

δ+

δ+

δ+

important water properties resulting from hydrogen bonding
Important Water Propertiesresulting from hydrogen bonding
  • high surface tension
  • low vapor pressure
surface properties
Surface Properties
  • a glass so filled with water that the surface isn’t flat but bulges above the rim
  • Meniscus
  • water forms nearly spherical droplets
slide6

The surface of water acts like a skin, as the water strider demonstrates.

  • The molecules within the liquid form hydrogen bonds with other molecules that surround them on all sides.
surface tension
surface tension
  • The inward force, or pull, that tends to minimize the surface area of a liquid
surfactant
surfactant
  • is any substance that interferes with the hydrogen bonding between water molecules and thereby reduces surface tension
vapor pressure
Vapor pressure
  • of a liquid is the result of molecules escaping from the surface of the liquid and entering the vapor phase.
  • Water has a relatively low vapor pressure
measurement of energy
Measurement of energy
  • Energy in various forms may be converted to heat,
  • heat units (calories or Joules) are used to measure the energies involved in chemical reactions.
joule don t copy til i explain
Joule – DON’T copy ‘til I explain
  • the amount of heat required to raise the temperature of one gram of water one Kelvin is 4.18 Joules.
  • 4.18 Joules = 1 calorie
  • 1 kilocalorie is equivalent to 1000 calories
  • 1 food Calorie = 1 kilocalorie = 1000 calories
  • Q = m c ΔT
  • where Q = heat measured in calories or Joules
  • where m = mass measured in grams
  • where c = Specific Heat measured in Joules/g0Cor Joules/gK(Regents have changed over to all Joules and Kelvin degrees).
  • where ΔT = change in temperature
specific heat
Specific Heat
  • Is the amount of heat required to change the temperature of a 1 gram sample 1 K (°Celsius).
  • is the amount of heat a sample can hold.
  • The Specific Heat for water is:
    • 4.18 Joules / gram K
    • See reference table B
evaporation vs vaporization
Evaporation vs. Vaporization
  • Evaporation is the process that describes a change from a liquid phase to a gaseous phase below the substance’s boiling point.
  • Vaporization is the process of liquid to gas at the boiling point.
  • These changes are Endothermic (requires energy in)
slide16

Condensationis the process that describes a change from a gaseous phase to a liquid phase.

  • This change is Exothermic (releases energy out)
heat during a phase change
Heat during a phase change
  • During a phase change temperature remains the same
  • Heat of vaporization (use at liquid-gas phase change)
  • Heat of Vaporization for water is 2260 Joules / gram
  • See reference table B
  • Heat of fusion (use at solid-liquid phase change)
  • Heat of Fusion for water is 334 Joules / gram
  • See reference table B
solvents and solutes
Solvents and Solutes
  • Solute - dissolved particles in a solution
  • Solvent - the dissolving medium in a solution
  • aqueous solution- water that contains dissolved substances
slide20

When a salt is added to water it dissociates and forms aqueous ions in solution.

  • Solvation- a process that occurs when an ionic solute dissolves; in solution, solvent molecules surround the positive and negative ions.
electrolytes and non electrolytes
Electrolytes and Non-electrolytes
  • Electrolyte- conducts an electric current when it is in an aqueous solution or in the molten state.
  • all ionic compounds are electrolytes, but most covalent compounds are not
  • Non-electrolyte- does not conduct an electric current in aqueous solution or in the molten state (i.e. pure water)
suspensions
Suspensions
  • a mixture where some of the particles settle out slowly upon standing.
  • differs from a solution because the particles of a suspension are much larger and do not stay suspended indefinitely.
  • are heterogeneous because at least two substances can be identified.
    • Ex. Mud water
colloids
Colloids
  • a heterogeneous mixture whose particles are intermediate in size (particles that range in size from 1 nm to 1000 nm) between those of a suspension and a solute solution.
  • The particles are spread throughout the medium, which can be a solid, liquid, or gas.
    • The first substances to be identified as colloids were glues.
    • Other colloids include such mixtures as gelatin, paint, aerosol spray, ice cream
emulsions
Emulsions
  • a colloidal dispersion of a liquid in a liquid.
  • An emulsifying agent forms an emulsion and maintains its stability.
    • e.g.oilsand greases are not soluble in water.
    • form a colloidal dispersion if soap or detergent is added to the water.
    • Soaps and detergents are emulsifying agents.
  • Mayonnaise is a heterogeneous mixture of oil and vinegar.
    • quickly separate without the presence of egg, which is the emulsifying agent.
soaps and detergents
Soaps and Detergents
  • One end of a large soap or detergent molecule is polar and is attracted to water molecules. “hydrophilic”
  • The other end of the soap or detergent molecule is non-polar and is soluble in oil or grease. “hydrophobic”
  • Soaps and other emulsifying agents thus allow the formation of colloidal dispersions between liquids that do not ordinarily mix.