This document discusses acids and bases. It defines acids as substances that produce H+ ions in water and bases as substances that produce OH- ions. Acids are classified as strong or weak depending on how fully they dissociate in water. Strong acids fully dissociate while weak acids only partially dissociate. The pH scale is used to measure acidity and alkalinity. Neutral solutions have a pH of 7 while acids have a pH less than 7 and bases have a pH greater than 7. Acid rain is caused by atmospheric pollutants like sulfur and nitrogen oxides dissolving in water to form acids. Some substances like carbonic acid and the amino acid glycine can act as both acids and bases, making

1. Acids and Bases
PGCC CHM 101 Sinex

2. General properties
ACIDS
• Taste sour
• Turn litmus
• React with active
metals – Fe, Zn
• React with bases
BASES
• Taste bitter
• Turn litmus
• Feel soapy or
slippery (react with
fats to make soap)
• React with acids
blue to red red to blue

3. Definitions
• Acids – produce H+
• Bases - produce OH-
• Acids – donate H+
• Bases – accept H+
• Acids – accept e-
pair
• Bases – donate e-
pair
Arrehenius
Bronsted-Lowry
Lewis
only in water
any solvent
used in organic chemistry,
wider range of substances

4. Examples
Arrhenius
Bronsted-Lowry
Lewis
HCl NaOH
HCl NH3
:NH3BF3
HCN
The hydrogen ion in aqueous solution
H+
+ H2O  H3O+
(hydronium ion)

5. The Bronsted-Lowry Concept
Conjugate pairs
HCl Cl- CH3COOH CH3COO-
NH4
+
NH3 HNO3 NO3
-
How does a conjugate pair differ?
H+
transfer

6. Neutralization
In general: Acid + Base  Salt + Water
All neutralization reactions are double displacement reactions.
HCl + NaOH  NaCl + HOH
HCl + Mg(OH)2 
H2SO4 + NaHCO3 

7. H2O  H+
+ OH-
Does pure water conduct electrical current?
(H+
)(OH-
) = 10-14
For pure water: (H+
) = (OH-
) = 10-7
M
This is neutrality and
at 25o
C is a pH = 7.
Water is a very, very, very weak electrolyte.
How are (H+
) and (OH-
) related?
water

8. HA
Let’s examine the behavior of
an acid, HA, in aqueous solution.
What happens to the HA molecules in solution?

9. HA
H+
A-
Strong Acid
100% dissociation of HA
Would the
solution be
conductive?

10. HA
H+
A-
Weak Acid
Partial dissociation of HA
Would the
solution be
conductive?

11. HA
H+
A-
Weak Acid
HA  H+
+ A-
At any one
time, only a
fraction of
the molecules
are
dissociated.

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

13. pH
2 3 4 5 6 7 8 9 10 11 12
neutral @ 25o
C
(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

14. You
are
here!
http://nadp.sws.uiuc.edu/isopleths
pH of Rainwater
across United States in 2001
Increasingacidity
Why is the eastern US more acidic?

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

16. 105
Db
107
Bh
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

17. When life goes either way
amphoteric (amphiprotic) substances
HCO3
-
H2CO3 CO3
-2
+ H+ - H+
Acting like
a base
Acting like
an acid
accepts H+
donates H+

18. pH
1 2 3 4 5 6 8 9 10 11
The biological view in the human body
gastricjuice
vaginalfluid
urinesaliva
cerebrospinalfluid
bloodpancreatic
juice
bile
acidic basic/alkaline
7
Tortora & Grabowski, Prin. of Anatomy & Physiology, 10th
ed., Wiley (2003)

19. Does the pH influence the
activity of an enzyme?
Trypsin is a digestive enzyme. Where?
Intestinal pH range 7.0-8.5

20. The amino acid glycine - amphoteric
It’s an acid and a base!
Loss of H+
Gain of H+
H2N-CH2-COOH
H3N+
-CH2-COOH H2N-CH2-COO-
Chime structure

21. The amino acid glycine - Zwitterion formation
Transfer of H+
from carboxylic
acid group to amine group.
H2N-CH2-COOH
H3N+
-CH2-COO-
+
-
A dipolar
ion forms.
intramolecular acid-base reaction
Chime structure

22. Show how water can be amphoteric.
H2O
+ H+ - H+

23. Dilution
water (solvent) solute
concentrated, Minitial
diluted, Mfinal
adding water lowers the solute concentration
moles of solute remain constant
Vinitial
Vfinal
molesinitial = molesfinal
Mfinal x Vfinal = Minitial x Vinitial

24. Titration Calculation
HCl + NaOH  NaCl + HOH
at equivalence point: moleHCl = moleNaOH
moles = M x VL
Macid x Vinitial acid = Mbase x Vburet
A way to analyze solutions!
indicator