Science%20Starter%209/23/15:

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Science Starter 9/23/15

• Hand in HW (States of Matter Webquest)
• What would be the effect on the properties of
  water molecules if oxygen and hydrogen had equal
  electronegativity?

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Science Starter 9/22/15

• With the person sitting next to you, think about
  the answer to this question
• If you had a glass of water filled TO THE BRIM
  with ice and water, once the ice melts, will the
  water overflow? Explain why or why not.

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Notes- Water
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Water is Amazing!!

• water covers 3/4 of Earths surface
• water is the main reason why life exists on
  Earth!
• water has many unique properties that allow it to
  be supportive of life on Earth

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Polarity of Water

• Water molecule two hydrogen atoms joined to an
  oxygen atoms via polar covalent bonding
• Result a molecule that has a slightly negative
  end (the O side) and a slightly positive end (the
  H side) Polar Molecule

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Polarity of Water

• When multiple water molecules are near each
  other, they form hydrogen bonds with each other
• the () H-side is attracted to the (-) O side
• creates a sticky molecule

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Properties of Water

• 1. cohesion and adhesion
• 2. good solvent
• molecules dissolve in water
• 3. lower density as a solid (ice floats!)
• 4. high specific heat
• water stores heat
• 5. high heat of vaporization
• heats cools slowly

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1. Cohesion Adhesion

• Cohesion
• hydrogen bonding between water molecules
• water is sticky
• results in surface tension
• Adhesion
• bonding between water molecules and a different
  substance
• meniscus on a graduated cylinder
• water climbs up paper towel

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2. Water is the universal solvent

• Since water is polar, it dissolves other polar
  substances easily
• like dissolves like
• The solvent dissolves the solute to form a
  solution

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Check-In
MOLECULE 1
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• different molecules
• red arrows indicate the direction electrons are
  being pulled
• with your seat partner, try to figure out which
  molecules are POLAR and which are NON POLAR

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3. Lower density as a solid

• Pretty much all substances are more dense as
  solids..
• But, ice floats!
• Hydrogen bonds form a crystal with space in
  between each molecule
• Ice has fewer molecules than an equal volume of
  water less dense

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Ice floats has many good effects

• If ice sank, eventually all ponds, lakes, and
  even the ocean would freeze solid!
• surface ice insulates the water underneath it
• allows life to continue in winter
• seasonal turnover of nutrients in lakes
• cold sinking water flushes up nutrients

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4. High specific heat

• Water resists changing temperature
• high specific heat
• takes a long time to heat up
• takes a long time to cool down
• water keeps Earths temperatures moderate
  (especially when you live near a large body of
  water!)

LONG ISLAND, NY
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5. High heat of vaporization

• water requires a large amount of heat in order to
  change from liquid to vapor
• evaporative cooling- as liquid evaporates, the
  liquid that remains behind cools down (the
  hottest molecules leave)
• organisms rely on evaporative cooling to maintain
  body temperatures!

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pH review..

• Water ionizes
• H splits off from OH-
• if H OH-, water is neutral, pH7
• if H gt OH-, water is acidic, pH under 7
• if H lt OH-, water is basic, pH over 7

H2O H OH
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pH scale

• if you go up or down by ONE on pH scale, it is
  actually 10x more or less H ions
• 0 ------gt 7 -------gt 14

MOST BASIC
NEUTRAL
MOST ACIDIC