Water
Today’s Topics
•  Polar Covalent Bonds
•  Hydrogen bonding
•  Properties of water
•  pH
•  Buffers
Non-polar
!–
Polar
+
H
+
•  Carbon Molecules
!–
H +
!–
!–
+
(if time)
7 Sept 2011
Like little magnets:
Water
S
N
S
N
S
N
Oxygen is more electronegative
than hydrogen
+
polar
covalent
bond
+
+
Partial negative
charge on the oxygen;
+
Partial positive on the
hydrogen.
+
+
+
+
Emergent Properties of
Water due to Polarity
Water conducting cells
Figure 3.4
100 !m
Figure 3.3
Hydrogen
bond
Ice
Hydrogen bonds are stable
Negative oxygen regions
of water molecules are attracted to
sodium cations (Na+).
–
Na+
+
–
–
Positive hydrogen regions
of water molecules
cling to chloride anions (Cl–).
Liquid water
Hydrogen bonds
constantly break and re-form
Na+
+
Cl–
Cl –
–
+
+
+
+
–
–
+
Water and Oil Don’t Mix
+
–
–
–
–
Figure 3.6
C- H bonds are Non-polar
Polar molecules dissolve in Water
“Like dissolves Like”
“Like dissolves Like”
Nonpolar molecules dissolve in nonpolar
solvents
NONpolar covalent molecules
do not dissolve in water
+
+
+
+
+
+
+
+
+
NONpolar covalent molecules
do not dissolve in water
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
H 2O
+
+
+
+
+
Time
+
+
+
H+
OH-
H
H
H
H
H
+
H
H
Hydronium
ion (H3O+)
+
H
Hydroxide
ion (OH–)
+
+
+
+
+
Because they disrupt hydrogen bonding
Definition: A mole
+
Only a tiny fraction
is ionized at any
moment
+
(or “mol”)
–  Represents an exact number of molecules
–  One mole is 6.02x1023 molecules
Molarity
•  Number of molecules per liter of solution
Mass
•  Hydrogen atom =1g/mole
•  Oxygen atom= 16 g/mole
•  Water (H2O)= 18g/mole
The product always equals 1x10-14
10-7 x 10-7 = 10-14
pH Scale
0
Increasingly Acidic
[H+] > [OH–]
1
2
3
4
5
6
Neutral
[H+] = [OH–]
Battery acid
Digestive (stomach)
juice, lemon juice
Vinegar, beer, wine,
cola
Tomato juice
Increasingly Basic
[H+] < [OH–]
Low pH
H+ abundant
-OH depleted
Black coffee
Rainwater
Urine
7 Pure water
Human blood
8
9
10
11
12
13
Figure 3.8
Buffers resist changes in pH
Seawater
Milk of magnesia
Household ammonia
Household bleach
Oven cleaner
14
Valence of 4
Diversity and Stability
High pH
H+ depleted
-OH abundant