Properties of Water

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Properties of Water
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Why is Water important?

• Life probably evolved in water.
• Living cells are 70-95 water
• Water covers 3/4 of the earth.
• Water naturally occurs in three states of matter.
• Life depends on the properties of water.

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• Water is a polar molecule. Its polar bonds and
  asymmetrical shape give water opposite charges on
  opposite sides.

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Polarity

• The polar molecules of water are held together by
  hydrogen bonds.

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Polarity

• Polar water molecules are attracted to ions and
  polar compounds, making them soluble.

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Benefit to life polarity

• Many kinds of molecules can move freely in cells,
  permitting a diverse array of chemical reactions.

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Properties of water

• 1. Cohesion
• 2. Adhesion
• 3. Surface tension
• 4. Hydophilic
• 5. Imbibition

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Properties of water

• 6. High specific heat
• 7. High Heat of vaporization
• 8. Freezing and expansion of water
• 9. Universal solvent
• 10. Capillary action

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Properties of water--cohesion

• 1. Cohesion--substances held together by
  hydrogen bonds--contributes to upward water
  transport in plants.

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Properties of water--adhesion

• 2. Adhesion of water to vessel walls counteracts
  the downward pull of gravity. Adhesion is the
  clinging of water to hydrophilic substances (such
  as glass).

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Properties of water--surface tension

• 3. Water has a strong surface tension because
  water molecules are held together by hydrogen
  bonds, water has a high degree of cohesion, or
  the ability to stick together.

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Properties of water--hydrophilic

• 4. hydrophilic--property of having an affinity
  for water.
• hydro-water
• philo-loving
• phobic-fearing

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• Ionic and polar substances are hydrophilic, but
  nonpolar compounds are hydrophobic. (not water
  soluble)

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Properties of water--imbibition

• 5. Imbibition--process of water soaking into a
  porous hydrophilic substance (like in a sponge).
  Imbibition in seeds, allows germination.

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High specific heat

• Water has a high specific heat, which means
  that it resists temperature changes when it
  absorbs or releases heat.

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High specific heat

• A large body of water can act as a heat
  sink--absorbing heat from the sun during the day
  and summer and releasing heat during the night
  and winter as the water gradually cools.

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High heat of vaporization

• 7. Vaporization (evaporation) transformation
  from liquid to gas. For water to evaporate,
  hydrogen bonds must be broken which requires heat
  energy.

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Freezing and expansion of water

• Water is densest at 4º C.
• 8. As water cools from 4º C to freezing, it
  expands and becomes less dense than liquid water
  (ice floats.)

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9. Universal solvent

• Solution--a liquid that is a homogenous mixture
  of 2 or more substances.
• Solvent--dissolving agent
• Solute--substance dissolved in a solution

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Capillary action

• 10. Two forces taken together--cohesion and
  adhesion account for the ability of water to rise
  in thin vessels of tens or hundreds of feet up
  the roots, trunks, and branches of even the
  largest trees.

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Acids, Bases, and pH

• Acids--substance that increases the H of a
  solution.
• Bases--substance that increases the OH- of a
  solution reduces the H of a solution.

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pH scale

• pH scale is used to measure degree of acidity.
  It ranges from 0 to 14.
• pH 7 is neutral
• lt 7 is acid gt 7 is basic

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pH scale

• Remember that the pH scale is a measure of
  hydrogen (H) ion concentration.

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pH

• A low pH corresponds to a high concentration of
  hydrogen ions.
• A high pH corresponds to a low concentration of
  hydrogen ions.

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pH scale

• pH scale is a logarithmic scale. A change of one
  pH number actually represents a tenfold change in
  hydrogen ion concentration. ex. pH 3 is ten
  times more acid than pH 4.

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pH of body fluids

• Most biological fluids have a pH between 6 and
  8.
• stomach acid with pH 1.5-2

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pH scale
 measures the number of H ions
Soren Sorensen (1868 - 1939)
ACID
BASE
10x
10x
10x
0 1 2 3 4 5 6
7 8 9 10 11 12 13
14
NEUTRAL
Each step on pH scale represents a factor of 10.
pH 5 vs. pH 6 (10X more acidic)
pH 3 vs. pH 5 (100X different)
pH 8 vs. pH 13 (100,000X different)