Water

Chapter 3

Water Life began in water 2/3’s of an organisms body Organisms grow or reproduce in a

water-rich environment. 

Water Molecule Covalent bonding Oxygen is more electronegative Polar molecule Polarity of water underlies its

chemistry Chemistry of life.

Polar molecule

Polar molecule

Hydrogen bonding

Fig. 3-2

Hydrogenbond

–H

+

H

O

——

——

+ +

+

–

–

–

Properties of water• Cohesion: • Attraction between water

molecules • Responsible for surface tension of

water

Properties of water Adhesion: Attraction of water between other

molecules Capillary action

Properties of water Moderation of water temperature Water is a liquid at moderate

temperatures Specific heat: Amount of heat needed to a raise

1 gram of a substance 10 Celsius Water’s specific heat is

1 calorie/gram/0C (4.18Joules)

Properties of water Evaporative cooling Heat of vaporization: Amount of heat needed to change

1 gram of a substance from a liquid to a gas.

586 Calories (2260 Joules)

Properties of water Ice floats Less dense

Fig. 3-6a

Hydrogenbond

Liquid waterHydrogen bonds break and re-form

IceHydrogen bonds are stable

Properties of water Solvent Water surrounds ionic & polar

molecules Table salt or sugar Aqueous solution Molarity

Fig. 3-7

Cl–

Na

Cl–

+

+

+

+

+

+

++

––

–

–

–

–

––

Na+

–

––

+

Hydrophobic “fear” of water Common in non-polar molecules Non-polar molecules tend to

aggregate in water Hydrophobic exclusion

Hydrophilic “water-loving” Common in polar molecules

Fig. 3-UN2

Hydroniumion (H3O+)

Hydroxideion (OH–)

2H2O

H

H

H

H

H

H

H

H

OOOO

Ionization

Process of spontaneous ion formation H2O H+ + OH-

Dissociation

pH Measurement of the concentration of

hydrogen ion. pH = -log[H+] Acid: Increase concentration of H+ ions or a

lower pH. Base: Decrease in concentration of H+ions or

a higher pH.

Fig. 3-UN5

Bases donate OH–

or accept H+ inaqueous solutions

Acids donate H+ inaqueous solutions

Acidic[H+] > [OH–]

Neutral[H+] = [OH–]

Basic[H+] < [OH–]

14

7

0

pH

Fig. 3-9

Neutral solution

Acidic solution

Basic solution

OH–

OH–

OH–

OH–

OH–OH–

OH–

H+

H+

H+

OH–

H+ H+

H+ H+

OH–

OH–

OH–OH–

H+

OH–

H+

H+

H+

H+

H+

H+

H+

OH–

Neutral [H+] = [OH–]

Incr

easi

ng

ly A

cid

ic [

H+]

> [

OH

–]

Incr

easi

ng

ly B

asic

[H

+]

< [

OH

–]

pH Scale0

1

2

3

4

5

6

7

8

Battery acid

Gastric juice,lemon juice

Vinegar, beer,wine, cola

Tomato juice

Black coffee

Rainwater

Urine

SalivaPure water

Human blood, tears

Seawater

9

10

Milk of magnesia

Household ammonia

Householdbleach

Oven cleaner

11

12

13

14

Buffer Substance helps maintain a

balanced pH Accepts H+ ions when excess Donates when there are too few.

Buffer Blood pH is approximately 7.4. Bicarbonate ion helps maintain

the pH of the blood. Blood acidosis: pH drops 0.2 to 0.4

points on the pH scale Blood alkalosis: pH goes up 0.2 to

0.4 points on the pH scale

Buffer Bicarbonate ion

H2CO3 ⇌ HCO3- + H+

Acid rain Sulfuric acid Nitric acid

Acid rain