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Basic Chemistry
Honors Bio
Ms. Napolitano
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Water is everywhere!
 The
Earth is ~71% water
 The
human body is
made up of about 5578% water
 Water
is a polar
molecule
 Molecules
of water are
held together by
hydrogen bonds
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Properties of Water
1.
Cohesion –the attraction of
H2O molecules to other H2O
molecules due to hydrogen
bonding
 Adhesion
– attraction of H2O
to other substances
 Capillary Action - ability of
H2O to move within narrow
spaces against gravity
 Surface Tension – cohesive
forces at the surface of H2O
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Properties of Water
2.
Expansion upon
freezing
 Solid
state is less dense
than liquid state
 Begins to expand at 4°C
 Floating ice creates
insulation for underneath,
allows for life in aquatic
ecosystems
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Properties of Water
3.
Universal solvent
Solute – substance being dissolved
 Solvent – dissolving agent
 Solution – homogenous mixture of 2 or more
substances
 Aqueous solution – water is the solvent
 Water forms a hydration shell around ionic
compounds
 Water dissolves polar compounds
 Hydrophilic – “water loving”, affinity for H2O
 Hydrophobic – “water fearing”, repels H2O

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Properties of Water
4.
Moderate Temperature

Specific Heat – amount of heat that must be
absorbed or lost for 1g of substance to change 1°C

Calorie – amount of heat to raise 1g of water by 1°C

Water has high specific heat: 1 cal/g/°C


Water has high heat of vaporization


Due to hydrogen bonding
Moderates climate
Evaporative cooling prevents organisms from
overheating
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10/21 - Do Now


Please take out your homework and a
piece of notebook paper.
Grab your clickers!
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Properties of Water
4.
Moderate Temperature

Specific Heat – amount of heat that must be
absorbed or lost for 1g of substance to change 1°C

Calorie – amount of heat to raise 1g of water by 1°C

Water has high specific heat: 1 cal/g/°C


Water has high heat of vaporization


Due to hydrogen bonding
Moderates climate
Evaporative cooling prevents organisms from
overheating
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Hydration Sphere
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Hydration Sphere
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pH
 Dissociation: the

 In
breaking apart of 2+ molecules
Usually capable of recombining
water, one H+ ion shifts from one molecule to the
other
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pH
 Acid
– increases H+ concentration of a solution
HCl  H+ + ClH2CO3  HCO3- + H+
 Base
– reduces H+ concentration of a solution
NH3 + H+  NH4+
NaOH  Na+ + OH-
 Acids
and bases that dissociate completely in
water are called strong acids and strong bases,
respectively.
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The pH Scale
 Measure
of H+
concentration
 pH
is lower as H+
concentration
increases
 pH
is higher as H+
concentration
decreases
 pH
7 = neutral
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Buffers
 Many
 Most
bodily processes are pH specific
living cells have pH of ~7
 Buffers
– substances that minimize change in H+
and OH- concentrations in a solution
 Accept
or donate H+ ions
 Usually
contain a weak acid and corresponding
base