Water and the Fitness of the Environment

Page
5

Acidic solutions have pH values less than 7

Basic solutions have pH values greater than 7

Most biological fluids have pH values in the range of 6 to 8

Slide 39

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–]

Increasingly Acidic

[H+] > [OH–]

Increasingly Basic

[H+] < [OH–]

pH Scale

0

1

2

3

4

5

6

7

8

Battery acid

Gastric juice,

lemon juice

Vinegar, beer,

wine, cola

Tomato juice

Black coffee

Rainwater

Urine

Saliva

Pure water

Human blood, tears

Seawater

9

10

Milk of magnesia

Household ammonia

Household

bleach

Oven cleaner

11

12

13

14

Slide 40

Buffers

The internal pH of most living cells must remain close to pH 7

Buffers are substances that minimize changes in concentrations of H+ and OH– in a solution

Most buffers consist of an acid-base pair that reversibly combines with H+

Slide 41

Threats to Water Quality on Earth

Acid precipitation refers to rain, snow, or fog with a pH lower than 5.6

Acid precipitation is caused mainly by the mixing of different pollutants with water in the air and can fall at some distance from the source of pollutants

Acid precipitation can damage life in lakes and streams

Effects of acid precipitation on soil chemistry are contributing to the decline of some forests

Slide 42

Fig. 3-10

More

acidic

0

Acid

rain

Acid

rain

Normal

rain

More

basic

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Slide 43

Human activities such as burning fossil fuels threaten water quality

CO2 is released by fossil fuel combustion and contributes to:

A warming of earth called the “greenhouse” effect

Acidification of the oceans; this leads to a decrease in the ability of corals to form calcified reefs

Slide 44

Fig. 3-11

EXPERIMENT

RESULTS

Calcification rate

(mmol CaCO3

per m2 per day)

[CO32–] (µmol/kg)