acids and bases

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