Lesson Overview

1
Lesson Overview

• 2.2 Properties of Water

2
THINK ABOUT IT

• Why study water in Biology?
• Biology is the study of living things, so why
  study something nonliving such as water?

3
The Water Molecule

• Water covers 3/4 of Earths Surface
• Single most abundant compound in living things
• Expands as it freezes
• Water is one of the few compounds found in a
  liquid state over most of Earths surface.

4
Polarity

• Electrically neutral
• Oxygen is on one end of the molecule and hydrogen
  is on the other.
• Oxygen has a stronger attraction for electrons

5
Polarity

• Oxygen has a negative charge
• Hydrogen has a positive charge.
• Polar Molecule molecule in which the charges are
  unevenly distributed
• The molecule is a bit like a magnet with two
  poles.

6
Hydrogen Bonding

• Partial positive and negative charges attract
  each other
• Hydrogen Bonding attraction between a hydrogen
  atom () and the oxygen atom (-)

7
Hydrogen Bonding

• Water is able to form multiple hydrogen bonds
• Hydrogen bonds are not as strong as covalent or
  ionic bonds.

8
Cohesion

• Cohesion an attraction between molecules of the
  same substance
• Because a single water molecule may be involved
  in as many as four hydrogen bonds at the same
  time, water is extremely cohesive.

9
Cohesion

• Causes water molecules to be drawn together,
  which is why drops of water form beads on a
  smooth surface
• Produces surface tension, explaining why some
  insects and spiders can walk on a ponds surface

10
Adhesion

• Adhesion attraction between molecules of
  different substances
• Explains the formation of a meniscus

11
Adhesion

• Capillary Action force that causes water to
  rise in a narrow tube against the force of
  gravity
• One of the forces that draws water out of the
  roots of a plant and up into its stems and
  leaves.
• Cohesion holds the column of water together as it
  rises.

12
Heat Capacity

• It takes a large amount of heat energy to cause
  molecules to move faster and raise the
  temperature of the water.
• Heat Capacity amount of heat energy required to
  increase temperature of a substance
• The heat capacity of water is relatively high.

13
Heat Capacity

• Large bodies of water, such as oceans and lakes,
  can absorb large amounts of heat with only small
  changes in temperature.
• This protects organisms living within from
  drastic changes in temperature.
• At the cellular level, water absorbs the heat
  produced by cell processes, regulating the
  temperature of the cell.

14
The Water Molecule

• How does the structure of water contribute to its
  unique properties?

15
The Water Molecule

• How does the structure of water contribute to
  its unique properties?
• Because water is a polar molecule, it is able to
  form multiple hydrogen bonds, which account for
  many of waters special properties.

16
Solutions and Suspensions

• Water is not always pure it is often found as
  part of a mixture.
• Mixture material composed of two or more
  elements or compounds that are physically mixed
  together but not chemically combined.

17
Solutions and Suspensions

• Living things are in part composed of mixtures
  involving water.
• Two types of mixtures that can be made with water
  are solutions and suspensions.

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Solutions

• All the components of a solution are evenly
  distributed throughout the solution.
• In a saltwater solution, table salt is the
  solutethe substance that is dissolved.
• Water is the solventthe substance that is doing
  the dissolving.

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Solutions

• Waters polarity gives it the ability to dissolve
  both ionic compounds and other polar molecules.
• Water easily dissolves salts, sugars, minerals,
  gases, and even other solvents such as alcohol.
• When a given amount of water has dissolved all of
  the solute it can, the solution is said to be
  saturated.

20
Suspensions

• Suspension mixture of H2O and non-dissolved
  particles that do not settle out
• Example Blood
• Mostly water
• Contains dissolved compounds, cells and other
  undissolved particles that remain in suspension

21
Acids, Bases, and pH

• Why is it important for cells to buffer
  solutions against rapid changes in pH?

22
Acids, Bases, and pH

• Why is it important for cells to buffer
  solutions against rapid changes in pH?
• Buffers dissolved in lifes fluids play an
  important role in maintaining homeostasis in
  organisms.

23
Acids, Bases, and pH

• Water molecules can split apart to form hydrogen
  ions and hydroxide ions.

24
The pH Scale

• pH scale measurement system that indicates the
  concentration of H ions in solution
• The pH scale ranges from 0 to 14.
• At a pH of 7, the concentration of H ions and
  OH ions is equal.

25
The pH Scale

• Acid compound that will form H ions in solution
• pH below 7
• More H ions than OH ions
• The lower the pH, the greater the acidity.

26
The pH Scale

• Base compound that will form OH- ions in
  solution
• pH above 7
• More OH ions than H ions.
• The higher the pH, the more basic the solution.

27
The pH Scale

• Each step on the pH scale represents a factor of
  10.

28
Buffers

• The pH in the human body must be kept between 6.5
  and 7.5 in order to maintain homeostasis
• If the pH is lower or higher, it will affect the
  chemical reactions that take place within the
  cells.

29
Buffers

• Buffer dissolved compounds in the body that
  help an organism control pH
• Weak acids or bases that can react with strong
  acids or bases to prevent sharp, sudden changes
  in pH

30
Buffers

• Adding acid to an unbuffered solution causes the
  pH to drop. If the solution contains a buffer,
  however, adding the acid will cause only a slight
  change in pH.