Water

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Water
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Earths Water

• We live on a planet that is dominated by water.
  More than 70 of the Earth's surface is covered
  with this simple molecule. Scientists estimate
  that the hydrosphere contains about 1.36 billion
  cubic kilometers of this substance mostly in the
  form of a liquid (water) that occupies
  topographic depressions on the Earth. The second
  most common form of the water molecule on our
  planet is ice. If all our planet's ice melted,
  sea-level would rise by about 70 meters.

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Why study water?

• There are many organisms in this world that can
  exist without oxygen, but all living creatures
  need water in order to survive. Human beings, for
  example are between sixty-five and seventy
  percent water. Most of the plants that we use for
  food are between eighty-five and ninety percent
  water by weight.

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And

• Water is used for life support in a variety of
  capacities ranging from habitats to reproduction
  to animal body functions (i.e. digest food,
  transport wastes, lubricate body joints, regulate
  temperature, and soften body tissues). It is
  clear that life as we know it could not exist on
  Earth without its most abundant and remarkable
  substance - water.

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Water properties

• Unique properties based on its structure
• Oxygen is more electronegative than hydrogen
• Electrons spend more time with oxygen than with
  hydrogen
• This unequal sharing causes the oxygen to be
  slightly negative and the hydrogens to be
  slightly positive.
• Polar covalent bond
• ie unequal sharing

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Polarity of Water

• Since opposite electrical charges attract, water
  molecules tend to attract each other, making
  water kind of "sticky." As the right-side diagram
  shows, the side with the hydrogen atoms (positive
  charge) attracts the oxygen side (negative
  charge) of a different water molecule.
• This attraction forms hydrogen bonds.

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Water Structure
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Why is polarity important?

• Polarity causes molecules to interact in unique
  ways that influence life
• Encourages formation of hydrogen bonds

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Water is sticky

• Water is attracted to other water. This is called
  cohesion. Water can also be attracted to other
  materials. This is called adhesion.

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Cohesion
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Surface Tension
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• The walls of alveoli are coated with a thin film
  of water this creates a potential problem.
  Water molecules, including those on the alveolar
  walls, are more attracted to each other than to
  air, and this attraction creates a force called
  surface tension. This surface tension increases
  as water molecules come closer together, which is
  what happens when we exhale our alveoli become
  smaller (like air leaving a balloon).
  Potentially, surface tension could cause alveoli
  to collapse and, in addition, would make it more
  difficult to 're-expand' the alveoli (when you
  inhaled). Both of these would represent serious
  problems if alveoli collapsed they'd contain no
  air no oxygen to diffuse into the blood , if
  're-expansion' was more difficult, inhalation
  would be very, very difficult if not impossible.
  Fortunately, our alveoli do not collapse
  inhalation is relatively easy because the lungs
  produce a substance called surfactant that
  reduces surface tension.

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Surfactants
Lung cells that produce surfactant
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Adhesion Capillary Action

• This phenomenon causes water to stick to the
  sides of vertical structures despite gravity's
  downward pull.
• Water's high surface tension allows for the
  formation of water droplets and waves, allows
  plants to move water (and dissolved nutrients)
  from their roots to their leaves, and the
  movement of blood through tiny vessels in the
  bodies of some animals.

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Capillary Action

• Surface tension is related to the cohesive
  properties of water. Capillary action however, is
  related to the adhesive properties of water. You
  can see capillary action 'in action' by placing a
  straw into a glass of water. The water 'climbs'
  up the straw. What is happening is that the water
  molecules are attracted to the straw molecules.
  When one water molecule moves closer to a the
  straw molecules the other water molecules (which
  are cohesively attracted to that water molecule)
  also move up into the straw. Capillary action is
  limited by gravity and the size of the straw. The
  thinner the straw or tube the higher up capillary
  action will pull the water

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Water movement in plants

• Plants take advantage of capillary action to pull
  water from the ground into themselves. From the
  roots water is drawn through the plant by another
  force, transpiration.

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Water Transport in Plants
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Terminology

• Heat amount of energy associated with the
  movement of atoms and molecules in matter
• Temperature measures the intensity of heat
• Calorie amount of energy needed to raise 1000g
  of water 1 degree C

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Specific Heat of Water

• Water has a high specific heat. Specific heat is
  the amount of energy required to change the
  temperature of a substance. Because water has a
  high specific heat, it can absorb large amounts
  of heat energy before it begins to get hot. It
  also means that water releases heat energy slowly
  when situations cause it to cool. Water's high
  specific heat allows for the moderation of the
  Earth's climate and helps organisms regulate
  their body temperature more effectively.

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• Water's high specific heat allows for the
  moderation of the Earth's climate and helps
  organisms regulate their body temperature more
  effectively.

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An Example

• One way to observe this characteristic is to heat
  an empty pan over a fire. The pan quickly becomes
  red hot and may start to bum. Place the same pan
  over the fire with water in it and the liquid
  will absorb some of the heat. The pan will again
  become hot but not as hot as before. The
  temperature of the water, even if it boils, will
  rise only a small amount compared to the
  temperature of the pan.

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Try It!A simple experiment!
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Simple Experiment

• A Pyrex measuring cup was filled with either
  water, rubbing alcohol, or air, and then heated
  in a pan of simmering water.
• In the case of the air, a plastic covering was
  fashioned for the measuring cup in order to keep
  the volume of air in the cup contained.
• Initially, the cup and its contents were at room
  temperature. The temperature of the simmering
  water in the pan was approximately 200 degrees
  Fahrenheit.
• A thermometer was placed in the measuring cup in
  order to measure the temperature of the contents
  of the cup.
• Temperature readings were taken every minute for
  ten minutes.
• The cup was then removed from the water and
  placed in a cold water bath where the temperature
  of the cup's contents was again measured every
  minute for ten minutes.

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Data for Specific Heat Activity
Time Water Alcohol Air
0 min 75 deg. F 75 deg. F 80 deg F
1 min 80 deg. F 83 deg. F 100 deg. F
2 min 84 deg. F 93 deg. F 118 deg. F
3 min 88 deg. F 106 deg. F 138 deg. F
4 min 94 deg. F 116 deg. F 158 deg. F
5 min 100 deg. F 126 deg. F 175 deg. F
6 min 106 deg. F 135 deg. F 185 deg. F
7 min 112 deg. F 143 deg. F 190 deg. F
8 min 119 deg. F 150 deg. F 192 deg. F
9 min 124 deg. F 155 deg. F 193 deg. F
10 min 129 deg. F 158 deg. F 193 deg. F
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Graphs of the temp. changes

• Heating vs. Cooling

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• A water molecule takes a large amount of energy
  with it when it evaporates

• This leads to evaporative cooling

Figure 2.12
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Physical properties of water

• Density
• Density increases as temp decreases
• Water max density 4 degrees C
• Molecules move apart
• Solvent properties
• Protects ions from one another
• Charged substances dissolve
• Universal solvent

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States of Water
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States of Water
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• Like no other common substance, water exists in
  nature in all three physical states

• as a solid
• as a liquid
• as a gas

Figure 2.10B
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Dont forget the water cycle!

• It is this quality which allows for the water
  cycle, the process whereby the Earth's water is
  moved by the energy of the sun and the force of
  gravity through a cycle of evaporation,
  condensation, precipitation and accumulation.

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Water is less dense as a solid.

• Most liquids contract (get smaller) when they get
  colder. Water is different. Water contracts until
  it reaches 4C then it expands until it is solid.
  Solid water is less dense that liquid water
  because of this. If water worked like other
  liquids, then there would be no such thing as an
  ice berg, the ice in your soft drink would sink
  to the bottom of the glass, and ponds would
  freeze from the bottom up (not good if you are a
  fish)!

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Density
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• Water is less dense as a solid than as a liquid
• When water freezes, it forms crystal structure
  which is spacious leading to increase in volume
• Thus ice floats in water
• This insulates the life underneath!

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More Characteristics

• Pure water has a neutral pH of 7, which is
  neither acidic nor basic.
• Pure water is a very poor conductor of
  electricity! If that is the
  case, why do we have to
  be so careful with our
  electrical appliances?

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Universal Solvent

• Water is called the "universal solvent" because
  it dissolves more substances than any other
  liquid. This means that wherever water goes,
  either through the ground or through our bodies,
  it takes along valuable chemicals, minerals, and
  nutrients.

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Even Proteins! Water soluble protein
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