Biol 1020 Ch. 3 Water
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Transcript Biol 1020 Ch. 3 Water
Chapter 3: What’s so great about water?
Copyright 2010 Scott A. Bowling
Life as we know it requires water:
all organisms mostly liquid water
most metabolism requires aqueous (water) medium
many organisms live in liquid water or in an
environment dominated by water in its various
states (solid, liquid, or gas)
.
Chapter 3: What’s so great about water?
Copyright 2010 Scott A. Bowling
Some numbers:
cells are typically 70% or more water by mass
about 75% of the Earth’s surface is covered by
liquid water
.
Chapter 3: What’s so great about water?
Copyright 2010 Scott A. Bowling
Some numbers:
cells are typically 70% or more water by mass
about 75% of the Earth’s surface is covered by
liquid water
But then, just being common on the Earth doesn’t make
something essential for life. A large percentage of
the Earth’s crust is sand, but we don’t consider
sand a requirement for life.
.
Chapter 3: What’s so great about water?
Copyright 2010 Scott A. Bowling
Some numbers:
cells are typically 70% or more water by mass
about 75% of the Earth’s surface is covered by
liquid water
But then, just being common on Earth doesn’t make
something essential for life. A large percentage of
the Earth’s crust is sand, but we don’t consider
sand a requirement for life.
What is it about water that makes it so special?
.
Copyright 2010 Scott A. Bowling
Chapter 3: What’s so great about water?
polar nature of water molecules
What properties of water are important
for life?
Acids and Bases
Some useful definitions
.
Copyright 2010 Scott A. Bowling
Chapter 3: What’s so great about water?
polar nature of water molecules
What properties of water are important
for life?
Acids and Bases
Some useful definitions
.
Copyright 2010 Scott A. Bowling
•
Draw a water molecule (structural
formula)
•
Then draw in four more around it that
are connected to it by hydrogen bonds.
.
polar nature of water molecules
oxygen atoms are electron seeking
(electronegative), especially compared to hydrogen;
thus for an oxygen-hydrogen bond:
Copyright 2010 Scott A. Bowling
the oxygen atom has a partial (-) charge
the hydrogen atoms have a partial (+) charge
.
Copyright 2010 Scott A. Bowling
polar nature of water molecules
the polar character of water allows water molecules to form up to 4 hydrogen bonds
.
Copyright 2010 Scott A. Bowling
•
Draw a water molecule (structural
formula)
•
Then draw in four more around it that
are connected to it by hydrogen bonds.
.
Copyright 2010 Scott A. Bowling
Chapter 3: What’s so great about water?
polar nature of water molecules
What properties of water are important
for life?
Acids and Bases
Some useful definitions
.
Copyright 2010 Scott A. Bowling
•
List and describe at least four properties
of water that result from its polar
nature/hydrogen bonds.
•
Describe how water acts as a
temperature buffer (creates temperature
stability).
.
What properties of water are
important for life?
all of this come in some way from
water’s polar nature hydrogen bonds
and similar interactions
Copyright 2010 Scott A. Bowling
water is the principal solvent in living things
water exhibits both cohesive and adhesive
forces
water helps maintain a stable temperature
ice (solid water) floats in liquid water
.
water is the principal solvent in living things
Copyright 2010 Scott A. Bowling
highly polar = excellent solvent for other polar
substances, and for ionic compounds
.
Copyright 2010 Scott A. Bowling
water is the principal solvent in living things
hydrophilic substances – interact readily
with water
hydrophobic substances – do not interact
readily with water
nonpolar substances
good components for membranes
.
Copyright 2010 Scott A. Bowling
water exhibits both cohesive and adhesive forces
cohesive forces: attraction of water molecules each other
give water a high surface tension
.
water exhibits both cohesive and adhesive forces
adhesive forces: water molecules to be attracted to
other kinds of molecules
Copyright 2010 Scott A. Bowling
how things are made wet
capillary action: water moving through narrow tubes
even against gravity
results from cohesion and adhesion
living organisms take advantage of this
.
water helps maintain a stable temperature
high specific heat of water temp. stability
Copyright 2010 Scott A. Bowling
specific heat – energy to raise the temp.
of 1 gram of something 1ºC
h-bonds make water specific heat high
1 calorie / gram ºC
comparatively, takes more energy
gain/loss to change water temp.
.
water helps maintain a stable temperature
high specific heat of water temp. stability
Copyright 2010 Scott A. Bowling
much of the ecosphere is water
most biological organisms >70% water
temperature stability is critical for most life
.
water helps maintain a stable temperature
high heat of vaporization of water helps cool
the ecosphere and biological organisms
Copyright 2010 Scott A. Bowling
heat of vaporization: energy to move 1 gram from
liquid to gas
.
water helps maintain a stable temperature
high heat of vaporization of water helps cool
the ecosphere and biological organisms
Copyright 2010 Scott A. Bowling
heat of vaporization: energy to move 1 gram from
liquid to gas
h-bonds make water specific heat high
540 calories / gram
.
water helps maintain a stable temperature
high heat of vaporization of water helps cool
the ecosphere and biological organisms
Copyright 2010 Scott A. Bowling
heat of vaporization: energy to move 1 gram from
liquid to gas
h-bonds make water specific heat high
540 calories / gram
organisms use this for cooling
examples: sweating; evaporative cooling of a leaf
.
Describe how water acts as a
temperature buffer (creates temperature
stability).
Copyright 2010 Scott A. Bowling
•
.
.
Copyright 2010 Scott A. Bowling
ice floats
Copyright 2010 Scott A. Bowling
liquid water becomes denser as it cools –
but only up to a point
.
ice floats
Copyright 2010 Scott A. Bowling
liquid water becomes denser as it cools –
but only up to a point
at 4ºC:
water begins to expand as it cools further
– that is, it gets less dense from then on –
due to hydrogen bonds becoming locked
in place
.
Copyright 2010 Scott A. Bowling
ice floats
at 0ºC:
ice freezes into a crystal
.
Copyright 2010 Scott A. Bowling
ice floats
at 0ºC:
ice freezes into a crystal
based on the hydrogen bonds
.
Copyright 2010 Scott A. Bowling
ice floats
at 0ºC:
ice freezes into a crystal
based on the hydrogen bonds
floating ice keeps lakes, etc., from freezing
solid and is important for temperature
cycling on the planet
.
List and describe at least four properties
of water that result from its polar
nature/hydrogen bonds.
Copyright 2010 Scott A. Bowling
•
.
Copyright 2010 Scott A. Bowling
Chapter 3: What’s so great about water?
polar nature of water molecules
What properties of water are important
for life?
Acids and Bases
Some useful definitions
.
Copyright 2010 Scott A. Bowling
•
Define acids and bases.
.
Acids and Bases
acids are proton donors
Copyright 2010 Scott A. Bowling
.
Acids and Bases
acids are proton donors
Copyright 2010 Scott A. Bowling
dissociates to yield hydrogen ions (H+) in solution
HA (an acid)
H+ + A- (an anion)
.
Acids and Bases
acids are proton donors
Copyright 2010 Scott A. Bowling
dissociates to yield hydrogen ions (H+) in solution
HA (an acid)
H+ + A- (an anion)
H+ = one proton (mostly)
.
Acids and Bases
acids are proton donors
Copyright 2010 Scott A. Bowling
dissociates to yield hydrogen ions (H+) in solution
HA (an acid)
H+ + A- (an anion)
H+ = one proton (mostly)
when the atom loses its electron to become a
hydrogen ion, all that remains is the nucleus
.
Acids and Bases
acids are proton donors
Copyright 2010 Scott A. Bowling
dissociates to yield hydrogen ions (H+) in solution
HA (an acid)
H+ + A- (an anion)
H+ = one proton (mostly)
when the atom loses its electron to become a
hydrogen ion, all that remains is the nucleus
thus, hydrogen ions are sometimes referred to
as protons
.
Acids and Bases
acids are proton donors
Copyright 2010 Scott A. Bowling
dissociates to yield hydrogen ions (H+) in solution
HA (an acid)
H+ + A- (an anion)
H+ = one proton (mostly)
when the atom loses its electron to become a
hydrogen ion, all that remains is the nucleus
thus, hydrogen ions are sometimes referred to
as protons
therefore, any substance that yields a proton is
an acid, or an acid is a proton donor
.
Acids and Bases
bases are proton acceptors
Copyright 2010 Scott A. Bowling
a base is a substance that can accept a proton
.
Acids and Bases
bases are proton acceptors
Copyright 2010 Scott A. Bowling
a base is a substance that can accept a proton
bases either dissociate in water to produce
hydroxide ions and a cation, or split water to form
a cation and hydroxide ion:
Na+ + OH-
NaOH
or
B (a base) + HOH
BH+ + OH-
.
Acids and Bases
Copyright 2010 Scott A. Bowling
water tends to slightly dissociate into hydrogen and hydroxide ions (H+
and OH-)
HOH
H+ + OH-
.
Acids and Bases
water tends to slightly dissociate into hydrogen and hydroxide ions (H+
and OH-)
Copyright 2010 Scott A. Bowling
HOH
H+ + OH-
in pure water, the concentrations of these ions are equal:
[H+] = [OH-] = 10-7 M
(note that the designation M stands for molar, the moles of a substance per liter of solution)
the product of these remains constant: [H+] x [OH-] = 10-14
acidic solutions have an elevated [H+], and thus reduced [OH-]
basic solutions have an elevated [OH-], and thus reduced [H+]
.
Copyright 2010 Scott A. Bowling
•
Define acids and bases.
.
What does pH stand for, and how does
the pH scale work?
Copyright 2010 Scott A. Bowling
•
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Acids and Bases
pH scale shorthand notation for
proton concentration of a solution
Copyright 2010 Scott A. Bowling
the pH is -log[H+]
pure water ( [H+]= 10-7 M ) has
pH = 7
pH < 7 is acidic; pH > 7 is basic
pH of most living cells is usually
~ 7.2 to 7.4
.
What does pH stand for, and how does
the pH scale work?
Copyright 2010 Scott A. Bowling
•
.
Copyright 2010 Scott A. Bowling
•
How do pH buffers work?
.
Acids and Bases
buffers minimize pH changes
Copyright 2010 Scott A. Bowling
weak acids and weak bases serve as buffers
living things use buffers to prevent dramatic changes in pH,
which can kill them
.
Acids and Bases
buffers minimize pH changes
Copyright 2010 Scott A. Bowling
weak acids and weak bases serve as buffers
living things use buffers to prevent dramatic changes in pH,
which can kill them
.
02.20 Buffer Formation
Slide number: 2
+
H2O
Water
CO2
Carbon dioxide
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
02.20 Buffer Formation
Slide number: 3
+
H2O
Water
CO2
Carbon dioxide
H2CO3
Carbonic acid
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
02.20 Buffer Formation
Slide number: 4
–
+
+
H2O
Water
CO2
Carbon dioxide
H2CO3
Carbonic acid
HCO3–
Bicarbonate
ion
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
+
H+
Hydrogen
ion
Fig. 2.19
Copyright 2010 Scott A. Bowling
•
How do pH buffers work?
.
Copyright 2010 Scott A. Bowling
Chapter 3: What’s so great about water?
polar nature of water molecules
What properties of water are important
for life?
Acids and Bases
Some useful definitions
.
Copyright 2010 Scott A. Bowling
Some useful definitions
solvent – a liquid into which a
substance dissolves
solute – the dissolved substance
solution = solvent + solute
salts – form from acids and bases
water is formed
the cation of the base and the anion of the
acid form the salt
HCl + NaOH
NaCl + HOH
.
Some useful definitions
electrolytes are salts, acids, or bases that form ions
in water and thus can conduct an electrical current
when dissolved in water (pure water is a poor
conductor of electricity, but put in a salt and it
becomes an excellent conductor)
nonelectrolytes are substances like sugar that
dissolve in water but do not become ionic
mixtures - a mixture of 2 or more elements and/or
compounds; they can be broken down into elements
and compounds by simple physical means. There
are two types:
Copyright 2010 Scott A. Bowling
heterogeneous mixtures - mixtures that are not of uniform
composition throughout - a living organism is a good
example
homogeneous mixtures - mixtures that are completely
uniform throughout - a salt water solution is a good example
.