Water

1
Water

• Chapter 9

2
Goals

• Know properties and reactions of water
• Draw the structure of water
• Understand hydrogen bonding
• Be familiar with methods of water purification,
  softening
• Understand the causes of water pollution

3
Importance of Water

• Body is 50 water
• Survive many days without food, only a few
  without water.
• Water is the universal solvent

4
Physical Properties of Water

• Colorless, odorless, tasteless
• Contracts upon cooling until freezes at 0C, then
  expands. Max Density 1g/ml
• This is why ice floats, and glass containers
  break in the freezer if full, frostbite kills
  tissue, and pipes burst.
• Boils at 100C unless atm pressure lower.
• Heat required to boil or evaporate

5
Structure of the Water Molecule

• Doesnt conduct electricity, so covalent.
• But O wants e- more than H so polar covalent.
• Like dissolves like. Polar compounds will
  dissolve in polar solvent. Non-polar compounds
  will dissolve in non-polar solvent. (oil and
  water)

6
Caution chemistry humor

• Two bears enter the water, one in Yosemite Natl.
  Park, the other in Alaska. Which one dissolves
  first?

7
Caution chemistry humor

• Two bears enter the water, one in Yosemite Natl.
  Park, the other in Alaska. Which one dissolves
  first?
• The one in Alaska, because its polar!

8
Hydrogen Bonding

• Opposite charges attract.
• Figure 9.2, p. 149
• Like, not love
• Weaker than ionic or covalent bonds.
• Functions
• Determine shape of proteins, stabilize DNA double
  helix.

9
Boiling Point

• When vapor pressure atm pressure
• At high altitudes, atm pressure lower, so bp
  lower, food doesnt get hot enough to cook
• Autoclave increases pressure to increase boiling
  point for sterilization.

10
Evaporation

• Requires energy, cooling process.
• Vapor pressure - the pressure where evaporation
  and condensation are in equilibrium
• Molecules bump into each other, at surface one
  escapes.
• Higher temp, faster bumping, more escape.

11
Chemical Properties

• Add electricity, water breaks into H2 and O2
  (electrolysis)
• Does not break down at high temperature or
  pressure.

12
Chemical Reactions

• Reacts with metal oxides to make metal hydroxides
  (bases!)
• Mg H2O -gt Mg(OH)2
• Reacts with nonmetal oxides to make acids
• CO2 H2O -gt H2CO3 (acid rain)
• Reacts with active metals to make bases and
  hydrogen
• 2Na 2H2O -gt 2NaOH H2

13
Forming Hydrates

• Anhydrous - contains no water
• CaCl2
• Solid form of a chemical that contains water in
  the crystal.
• CaCl2 2H2O
• Efflorescent - If lose water
• Hygroscopic - if gain water (lye)

14
Hydrolysis

• Water breaks apart the compound
• Occurs in digestion
• NaCl H2O -gt NaOH HCl

15
Water Purification

• Impurities
• Dissolved, particulate, or bacterial
• Remove by
• Distillation - boil water and condense steam.
  Doesnt remove dissolved gas.
• Boiling - kills bacteria, temporarily removes
  dissolved gas
• Sedimentation and Filtration - removes
  particulate, not bacteria or dissolved gas.
• Aeration - kills bacteria

16
Hard vs. Soft Water

• Hard water contains dissolved Ca2
• and Mg2.
• Hard water precipitates with soap to make soap
  scum. Detergents dont.
• Soft water has other dissolved minerals, but not
  Ca2 or Mg2. Ammonia or sodium replace Ca2 and
  Mg2 in water softening units.

17
Fluoridation of Water

• Some cities add fluoride to drinking water
• (not Walla Walla)
• Purpose - to prevent cavities.

18
Water Pollution

• Pollutants prevent normal use of water
• Oxygen demanding waste- high organic matter, uses
  O2 as it decomposes.
• Disease causing agents - bacteria (cholera,
  typhoid)
• Radioactive material - would cause cancer
• Heat - decreases amount of dissolved O2
• Plant nutrients - nitrates, phosphates cause
  algae growth
• Synthetic organic chemicals - estrogens,
  antidepressants
• Inorganic chemicals and nutrients - mercury