Biology 102 A

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Biology 102 A

• Properties of Water
• And
• Acids/Bases

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Describe the properties of water that make it
important to living things.

• Water is polar it has an uneven distribution of
  electrons between the hydrogen and oxygen atoms
• One side of water is positive and the other is
  negative

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Water properties

• Water is cohesive
• Cohesion attraction between same molecules,
  causes molecules to draw inward at surface
• Ex allows some insects spiders can walk on
  the surface
• Water is adhesive
• Adhesion attraction between different molecules,
  causes water to bend at the surface
• Ex capillary action-pulls column of water up to
  the top of a plant

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Water properties

• Water is called Universal solvent dissolves
  many other substances due to polarity
• Differences in charges pulls/pushes substances
  apart
• Water exhibits evaporative cooling removes heat
  when it evaporates from a surface
• Ex sweating cools skin
• Water expands during freezing expands into
  crystal formation releasing heat
• Ex rocks broken up by ice creating soil ice
  layer protects fruit from freezing

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Acids, Bases and the pH scale

• The pH scale measures the concentration of H
  ions (how acidic something is)
• Ranges from 0-14
• At 7 H ions and OH- ions are equal so it is
  neutral
• 0-7 acidic, has more H ions
• 7-14 basic, has more OH- ions

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• ACIDS release H when mixed with water
• Sour, corrosive
• Ex HCl, H2SO4
• Always have H at front of formula
• BASES release OH- when mixed with water
• Bitter, slippery, usually in cleaners
• NaOH, CaOH
• Always have OH at end of formula

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What is a buffer?

• Buffers are weak acids or bases that react with
  strong acids and bases to prevent sharp changes
  in pH
• Helps to neutralize
• Help to control pH in blood, digestive tract,
  etc. to maintain homeostasis

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Quiz 3

• Your saliva measures 7 on the pH scale, it is
  a(n) ___ solution?
• a. acidic b. basic
  c. neutral
• The ___ property of water helps in the formation
  of soil.
• a. capillary action b. expansion during
  freezing c. evaporative cooling
• Laundry detergent typically has a pH of 3 which
  indicates a(n) ___ solution?
• a. acidic b. basic
  c. neutral
• The use of ___ helps to maintain a certain pH in
  our bodies maintaining homeostasis.
• a. buffers b. bases c.
  acids
• The ___ property of water removes heat helping to
  cool your skin through sweating.
• a. capillary action b. evaporation c.
  cohesion

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Create and Design

• Your assignment is to create and design a
  colorful and visually pleasing pH scale. Using
  pg 165 in your book to help you, create a scale
  of reference to show what some common substances
  pH numbers are. Use different colors and sketch
  pictures of the common items.
• Pick up a piece of paper and get started.