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Chapter 2: The Chemistry of Life
Chapter 2: The Chemistry of Life
2–2
Properties of Water
Mr. M. Varco
St. Joseph High School
2.2: The Water Molecule
•  Like other molecules, water is considered electrically neutral
–  Its 10 protons (+) balance of its 10 electrons (-)
•  With 8 protons, water’s oxygen nucleus attracts electrons more
strongly that the 1 proton of water’s two Hydrogen atoms
•  As a result, water’s shared electrons are more likely to be found
near the oxygen atom
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2.2: The Water Molecule
•  Because the oxygen nucleus is at one end of the molecule, water
has a partial negative charge on one end, and positive charge on
the other.
•  A molecule in which the charges are unevenly distributed is said
to be polar
•  Water molecules are polar
2.2: The Water Molecule
Hydrogen Bond:
•  The attraction between a hydrogen atom with a partial (+) charge
and another atom with a partial (-) charge is a hydrogen bond
•  Hydrogen Bonds are weaker than both Ionic and Covalent Bonds
•  Because water is polar, it can form
many hydrogen bonds
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2.2: The Water Molecule
•  Cohesion: An attraction between molecules of the same
substance
–  Water is cohesive. Why?
–  Because a single water molecule can be involved with up to four hydrogen
bonds at once
•  Adhesion: An attraction between molecules of a different
substance
2.2: Solution and Suspensions
•  A mixture is a material composed of two or more elements or
compounds that are physically mixed together, but not chemically
combined
•  Two types of mixtures are solutions and suspensions
+
= Mixture
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2.2: Solution and Suspensions
•  Solutions:
–  Solutions form when all of the components in a substance are uniformly
distributed throughout.
Cl-
ClNa+
Na+
Water
Water
2.2: Solution and Suspensions
•  Solutions:
–  In a saltwater solution, table salt is the solute, and water is the solvent
–  A solute is the substance that is dissolved
–  A solvent is the substance in which the solute is dissolved
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2.2: Solution and Suspensions
•  Solutions:
–  Water’s polarity allows it to dissolve both ionic compounds and other
polar molecules.
–  When a given amount of water has dissolved all of the solute, it is said
to be saturated
2.2: Solution and Suspensions
•  Suspensions:
–  Mixtures composed of water and non-dissolved material, where the
movement of water molecules keeps the small particles suspended
–  Example: Blood in our body
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2.2: The pH Scale
•  pH Scale:
–  The purpose of the pH scale is to determine the concentration of H+ ions
in a solution
–  The pH scale ranges from 0 – 14:
•  Acidic (pH below 7):
•  Neutral (pH = 7) :
•  Basic (pH above 7) :
Solutions with more H+ ions than OH- ions
Solutions with equal H+ ions and OH- ions
Solutions with less H+ ions than OH- ions
2.2: The pH Scale
•  pH Scale:
–  Each step on the pH scale represents a factor of 10
•  pH of 4 has 10 times as many H+ ions as pH of 5
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2.2: Acids, Bases, and Buffers
•  Where do the extra H+ ions in a low pH solution come from?
–  Acids: any compound that forms H+ ions in a solution
•  Base: a compound that produces hydroxide (OH-) ions
–  Strong bases have pH between 11-14
•  Water is considered neutral (pH = 7). Why?
–  When water molecules split, H+ ions and OH- ions are released
–  But…the number of H+ ions and OH- ions are equal
2.2: Acids, Bases, and Buffers
•  How does our body regulate the pH of the fluids within our body
to stay between 6.5 and 7.5?
–  Buffers: weak acids or bases that can react with strong acids or bases to
prevent sudden change in pH.
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