Transcript CHAPTER 2“Chemistry of Life”

CHAPTER 2
“Chemistry of Life”
Water & solutions
(Section 3 only)
REVIEW OF SECTION 1 & 2
• Matter is anything that occupies _______ and
that has mass.
• Elements are substances that cannot be
broken down ______ into simpler kinds of
matter.
• An atom is the simplest part of an element
• Compounds are made up of _____
or more elements in fixed proportions.
Polarity of Water
• In a water molecule, the hydrogen and oxygen atoms
____ electrons to form covalent bonds. (Covalent
bonds form when two atoms share one or more pairs
of electrons)
• Water molecules as a whole have no net _____, but
the oxygen end has a slight negative charge, and the
hydrogen end has a slight positive charge.
• For this reason, water is referred to as a
_______ molecule.
It has a positive end and a negative end
Solubility
• The polar nature of water allows it to ______
polar substances. Water does not dissolve
nonpolar substances because a weaker
attraction exists between polar and nonpolar
molecules
Hydrogen Bonding
• A hydrogen bond is the force of attraction between a _______
molecule with a partial positive charge and another atom or
molecule with a partial or full negative charge.
• The polar nature of water also causes water
molecules to be ________ to one another.
• The positively charged
region of one water
molecule is attracted to the
negatively charged region
of another water molecule.
COHESION
ADHESION
• An attractive force that
_____ molecules of a single
substance together is called
cohesion.
• Related to cohesion is
___________ of water. The
cohesive forces in water
resulting from hydrogen
bonds cause the molecules
at the surface to be pulled
downward into the liquid.
As a result, water acts as if it
has a thin “skin” on its
surface.
• Adhesion is the attractive
force between two particles
of _______ substances,
such as water molecules
and glass molecules.
Specific Heat
• Water has a high specific heat. Specific heat
is the amount of heat required to _____ the
temperature of one gram of a substance 1
degree Celsius.
• For example, water can absorb more solar energy without its
temperature increasing. Go to the beach on a hot summer day,
and notice the temperature of the sand and the water. In the
middle of the afternoon, the sand will feel hot, and the water
cool. At midnight, the sand will feel cool, and the water
temperature will be about the same. The sand changes its
temperature through the course of the day, but the water
temperature doesn't change much.
SOLUTIONS
• A solution is a _______ in which one or more
substances are uniformly distributed in
another substance.
• A solute is a substance dissolved in the
________.
• A solvent is the substance
in which the solute
is dissolved.
Acids & Bases
• As water molecules move around, they bump into one
another. Some of these collisions are strong enough to result
in a chemical ______: one water molecule loses a proton(a
hydrogen nucleus), and the other gains this proton.
*H2O ↔ H+ + OH The OH – ion is the ________ ion
- The free H+ ion can react with another water molecule as
shown below…
• H+ + H2O ↔ H3O+
The H3O+ is the ___________ ion
Acids
• If the number of hydronium ions in a solution is
________ than the number of hydroxide ions, the
solution is an acid
• Examples:
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Hydrochloric acid (HCl) in gastric juice
Sulphuric acid (H2SO4)
Nitric acid (HNO3)
Carbonic acid in softdrink (H2CO3)
Uric acid in urine
Ascorbic acid (Vitamin C) in fruit
Citric acid in oranges and lemons
Acetic acid in vinegar
Tannic acid (in tea and wine)
Tartaric acid (in grapes)
Bases
• If the number of hydroxide ions in a solution is
greater than the number of hydronium ions,
the solution is a ______
• Examples:
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Sodium hydroxide (NaOH) or caustic soda
Calcium hydroxide ( Ca(OH)2 ) or limewater
Ammonium hydroxide (NH4OH) or ammonia water
Magnesium hydroxide ( Mg(OH)2 ) or milk of magnesia
Many bleaches, soaps, toothpastes and cleaning agents
PH & Buffers
• Scientists have developed a scale for comparing
the relative _______ of hydronium ions and
hydroxide ions in a solution, called the PH scale
ranging from 0-14.
• ______ are chemical substances that neutralize
small amounts of either an acid or a base added
to a solution.
INDICATORS
An indicator, when added to an acid, a neutral substance or a base, will change
different colors.
INDICATOR
COLOR IN ACID
COLOR IN NEUTRAL
SOLUTION
COLOR IN BASE
Litmus
red
purple
blue
Bromothymol Blue
yellow
blue
blue
Phenolphthalein
clear
clear
purple
Universal Indicator
red
Yellow-green
purple