CHAPTER 3

CHAPTER 3
WATER AND THE FITNESS OF THE ENVIRONMENT

I. Life on Earth has evolved around water.

Living cells are 70%-95% water.

II. The Polarity of Water

Bent shape + difference in electronegativity = polar compound.
Up to 4 hydrogen bonds can form around water.

III. Important properties of water include...

Cohesion
Adhesion
Expansion upon freezing
High specific heat capacity
Versatile solvent

A. High cohesion properties -water H-bonds to other water molecules.

B. High adhesion properties-H-bonding of water to other substances.

C. Expansion upon Freezing

1. Frozen water (ice) is less dense than liquid water.

Due to structure of H-bonds

2. Environmental impact

Prevents large bodies of water from freezing solid.

Ice insulates the water below.

Pond life survives winters.

D. Water's high specific heat capacity

Resists temperature changes when it absorbs or releases heat.

1. Environmental Impact-

Large bodies of water can act as heat sinks.

E. Water -The solvent of life

Solution-homogeneous mixture of 2 or more substances.
Solvent-dissolving agent of the solution.
Solute-substance being dissolved.
Aqueous solution-solution where the solvent is water.

1. Water is a versatile solvent Dissolves-

Terminology =

2. Understanding molarity

What is a mole (mol)?

What is molarity (M)?

IV. pH, pOH, acids, bases and buffers. A. .

B. Dissociation of H₂O

C. pH

D. pH scale

pH	[H+]	[OH-]	pOH
0	1 M	1 x 10 ^-14 M	14
1	0.1 M	1 x 10 ^-13 M	13
2	0.01 M		12
3	0.001M		11
4	1 x 10 ^-4 M		10
5
6
7	1 x 10 ^-7 M	1 x 10 ^-7 M	7
8
9
10
11
12
13
14	1 x 10 ^-14 M	1 M	0

pH = _________
as pH increases, the [H+] decreases
[H+] is inversly propotional to [OH-]
[H+] x [OH-] = 1 x 10 ^-14 M²

What is pOH?

pOH = _________

pH + pOH = 14

Neutral solution
Acidic solution
Basic (alkaline) solution

E. pH of some common substances

F. Acids and Bases

ACID

BASE

Substance that increases the relative [H+] of a solution.

Also removes OH^- because it tends to combine with H+ to form H₂O

(Example)

Substance that reduces the relative [H+] of a solution.

May alternatively increase [OH-]

Base that directly reduces [H+] :

(Example)

Base that indirectly reduces [H+]:

(Example)

G. Buffers Buffer-

Blood pH...
.
.

Buffers consist of weak acids and their ions (salts).
Example:

pH 6.9

[H+] has increased in the blood

pH 7.7
[H+] has decreased in blood