Acids and Bases. General properties

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2

HA  H+ + A-

At any one time, only a fraction of the molecules are dissociated.

Slide 12

Strong and Weak Acids/Bases

Strong acids/bases – 100% dissociation into ions

HCl NaOH

HNO3 KOH

H2SO4

Weak acids/bases – partial dissociation, both ions and molecules

CH3COOH NH3

Slide 13

pH

2

3

4

5

6

7

8

9

10

11

12

neutral @ 25oC

(H+) = (OH-)

distilled water

acidic

(H+) > (OH-)

basic or alkaline

(H+) < (OH-)

natural waters pH = 6.5 - 8.5

normal rain (CO2)

pH = 5.3 – 5.7

acid rain (NOx, SOx)

pH of 4.2 - 4.4 in Washington DC area

0-14 scale for the chemists

fish populations

drop off pH < 6 and to zero pH < 5

Slide 14

You are here!

http://nadp.sws.uiuc.edu/isopleths

pH of Rainwater

across United States in 2001

Why is the eastern US more acidic?

air masses

Slide 15

What is acid rain?

CO2 (g) + H2O  H2CO3  H+ + HCO3-

Dissolved carbon dioxide lowers the pH

Atmospheric pollutants from combustion

NO, NO2 + H2O …  HNO3

SO2, SO3 + H2O …  H2SO4

both

strong

acids

pH < 5.3

Slide 16

Behavior of oxides in water– Group A

basic

amphoteric

acidic

3A 4A 5A 6A 7A

1A

2A

8A

Group B

basic: Na2O + H2O  2NaOH

(O-2 + H2O  2OH-)

acidic: CO2 + H2O  H2CO3

Slide 17

When life goes either way

amphoteric (amphiprotic) substances

HCO3-

H2CO3

CO3-2

Acting like

a base

Acting like an acid

accepts H+

donates H+

Slide 18

pH

1

2

3

4

5

6

8

9

10

11

The biological view in the human body

gastric juice

vaginal fluid

urine

saliva

cerebrospinal fluid

blood

pancreatic juice

bile

acidic

basic/alkaline

7

Tortora & Grabowski, Prin. of Anatomy & Physiology, 10th ed., Wiley (2003)

Slide 19

Does the pH influence the activity of an enzyme?

Trypsin is a digestive enzyme. Where?

Intestinal pH range 7.0-8.5

Slide 20