1

Water has no taste, no color, no odor; it cannot be defined, art relished while ever

mysterious.

Not necessary to life, but rather life itself. It fills us with a gratification that exceeds the

delight of the senses.

2

Water: The Molecule That Supports All of Life

3

• The following are pH values: cola– 2; orange juice– 3; apple juice– 4; coffee– 5; human blood– 7.4. Which of these liquids has the highest molar concentration of OH-?

a) cola

b) orange juice

c) Apple juice

d) coffee

e) human blood

4

• Based on your knowledge of the polarity of water, the solute molecule is most likely *

a) positively charged.

b) negatively charged.

c) neutral in charge.

d) hydrophobic.

e) nonpolar.

5

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6

Water molecules are polar

Fig. 2.10

7

Hydrogen bonding in water

Hydrogenbonds

+

+

H

H+

+

–

–

–

–

8

Hydrogen bond formation in water

• A dynamic phenomenon

http://www.nationmaster.com/encyclopedia/Hydrogen-bond

9

Hydrogen bonds in ice and water

Liquid water

Hydrogen bonds constantly break and re-form

IceHydrogen bonds are stable

Hydrogen bond

What about hydrogen bonds between molecules in water vapor?

10

Four emergent properties of water contribute to Earth’s fitness for life

1. Cohesion & adhesion

2. Moderation of temperature

3. Floating ice - insulation

4. Excellent solvent

All related to hydrogen bonding

11

1. Cohesion: Water molecules stick together

• The hydrogen bonding of a high percentage of the molecules to neighboring molecules

12

1. Cohesion

• Helps pull water up through the microscopic vessels of plants

Water conducting cells

100 µm

CO2

H2O

O2

H2O andminerals

13

1. Cohesion

• Surface tension is a measure of how hard it is to break the surface of a liquid

14

1. Adhesion

• How does capillary action work?

Fig. 2.13

15

2. Moderation of Temperature

• Water moderates air temperature– By absorbing heat from air that is warmer

and releasing the stored heat to air that is cooler

WHY?

16

2. Moderation of temperature - heat v.s. temperature

• Kinetic energy is energy of motion.

HeatIs a measure of the total amount of kinetic energy due to molecular motion

TemperatureMeasures the intensity of heat - not total energy

17

Which has more heat if both are the same temperture?

2. Moderation of temperature - heat v.s. temperature

18

2. Moderation of Temperature:Water’s High Specific Heat

• The specific heat of a substance– Is the amount of heat that must be absorbed for 1 gram

of that substance to raise its temperature by 1ºC

Water has a high specific heat; minimizes temperature fluctuations. Why?

19

2. Moderation of Temperature: Evaporative Cooling

• Heat of vaporization: the quantity of heat a liquid must absorb for 1 gram of it to be converted from a liquid to a gas

Evaporative coolingIs due to water’s high heat of vaporizationAllows water to cool a surface

20

3. Insulation of Bodies of Water by Floating Ice

Liquid water

Hydrogen bonds constantly break and re-form

IceHydrogen bonds are stable

Hydrogen bond

Why does ice float? Why is it important that ice floats?

21

4. The Solvent of Life

• Why is polarity important?

http://www.wou.edu/las/physci/ch412/dis_nacl.mov

22

Positive hydrogen regions of water molecules cling

to chloride anions (Cl–).Figure 2.14

Water molecules

Salt crystal

Cl–

Na+

Cl–

+

+

+

+

+

– –

–

––

Na+

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Hydration shells

Negative oxygen regions of polar water molecules are

attracted to sodium cations (Na+).

4. The Solvent of Life

23

pH

• Dissociation of water molecules leads to acidic and basic conditions that affect living organisms

24

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25

Dissociation of water• Water dissociates into hydronium ions and

hydroxide ions

H

Hydroniumion (H3O+)

H

Hydroxideion (OH–)

H

H

H

H

H

H

+ –

+

Simplified: H2O ↔ H+ + OH-

Pure water: [H+] = 10-7 M [OH- ] = 10-7 M Changes in the concentration of these ions affect living organisms

(note: [X] means concentration of substance X.)

26

Definition of pH

• The pH of a solution– Determined by relative concentration of H+

pH = = -log[H ]+1

log[H ]+

27

Acids and Bases

• An acid increases the hydrogen ion concentration [H+] of a solution

• A base reduces the hydrogen ion concentration [H+] of a solution

28

The logarithmic pH scale 0

pH Scale

Low pH: high H+, low OH-, acid

High pH: low H+, high OH-, basic

Fig. 2.15

29

Things to note about pH

• pH scale is logarithmic: [H+] changes 10-fold for each pH unit

• [H+] x [OH-] = 10-14

– At pH 5, [H+] = 10-5 M and [OH-] = 10-9 M

• The internal pH of cell cytoplasm held close to pH 7

30

Buffers

• Buffers minimize pH changes– Absorb or release H+ as necessary

Fig. 2.16

31

• The following are pH values: cola– 2; orange juice– 3; apple juice– 4; coffee– 5; human blood– 7.4. Which of these liquids has the highest molar concentration of OH-?

a) cola

b) orange juice

c) Apple juice

d) coffee

e) human blood

32

• Based on your knowledge of the polarity of water, the solute molecule is most likely *

a) positively charged.

b) negatively charged.

c) neutral in charge.

d) hydrophobic.

e) nonpolar.