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
only in water
Bronsted-Lowry
any solvent
Lewis
used in organic chemistry,
wider range of substances

4. Examples The hydrogen ion in aqueous solution
H H2O  H3O+ (hydronium ion)
Examples
Arrhenius
HCl
NaOH
Bronsted-Lowry
HCl
HCN
NH3
Lewis
BF3
:NH3

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

6. Neutralization HCl + NaOH  NaCl + HOH HCl + Mg(OH)2 
In general: Acid Base  Salt + Water
All neutralization reactions are double displacement reactions.
HCl NaOH  NaCl HOH
HCl Mg(OH)2 
H2SO NaHCO3 

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

8. Let’s examine the behavior of an acid, HA, in aqueous solution.
CHM 101
Let’s examine the behavior of an acid, HA, in aqueous solution.
Sinex HA
What happens to the HA molecules in solution?

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

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

11. At any one time, only a fraction of the molecules are dissociated.
HA  H A- HA H+
Weak Acid 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 acid rain (NOx, SOx) pH of 4.2 - 4.4 in Washington DC area
0-14 scale for the chemists 2 3 4 5 6 7 8 9 10 11 12
acidic
(H+) > (OH-)
25oC
(H+) = (OH-)
distilled water
basic or alkaline
(H+) < (OH-)
normal rain (CO2)
pH = 5.3 – 5.7
fish populations
drop off pH < 6 and to zero pH < 5
natural waters pH =

14. across United States in 2001
pH of Rainwater
across United States in 2001
You are here!
air masses
Increasing acidity
Why is the eastern US more acidic?

15. What is acid rain? Dissolved carbon dioxide lowers the pH
CO2 (g) + H2O  H2CO3  H+ + HCO3-
Atmospheric pollutants from combustion
NO, NO H2O …  HNO3
both
strong
acids
SO2, SO H2O …  H2SO4
pH < 5.3

16. Behavior of oxides in water– Group A
105 Db
107 Bh
basic
amphoteric
acidic 8A 1A
3A 4A 5A 6A 7A 2A
Group B
basic: Na2O + H2O  2NaOH
(O H2O  2OH-)
acidic: CO H2O  H2CO3

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

18. pH The biological view in the human body acidic basic/alkaline saliva1 2 3 4 5 6 7 8 9 10 11
saliva
blood
urine
gastric juice
vaginal fluid
pancreatic juice
bile
cerebrospinal fluid
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

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

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

22. Show how water can be amphoteric.

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

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