Lecture 19.3 for Prep Chemistry

1. BELLWORK- pH calcs
Determine the pH of the following solutions.
a) [H+] = 5.2x10-9 M (estimate)
b) [OH-] = 4.9x10-4 M (estimate)
c) pOH = 5.7
d) 0.01M HNO3
e) 0.10M NaOH

2. 19.3- Weak vs. Strong
Lemons and grapefruits
have a sour taste because
they contain citric acid.
Sulfuric acid is a widely
used industrial chemical
that can quickly cause
severe burns if it comes into
contact with skin.
You will learn why some
acids are weak and some
acids are strong.

3. Strong acids and bases
completely dissociate

4. Strong acids and bases
completely dissociate
AT EQUILIBRIUM
HCl + H2O  Cl- + H3O+
little lots lots

5. Weak acids and bases
only partly dissociate.

6. Weak acids and bases
only partly dissociate.
When in water most of the weak acid
will keep its proton attached.

7. Weak acids and bases
only partly dissociate.
When in water most of the weak acid
will keep its proton attached.
Acetic acid(vinegar) is a weak acid.

8. Weak acids and bases
only partly dissociate.
When in water most of the weak acid
will keep its proton attached.
Acetic acid(vinegar) is a weak acid.
AT EQUILIBRIUM
CH3COOH + H2O  CH3COO- + H3O+
lots little little

9. Which acid will produce more H+,
1M HCl or 1M acetic acid?

10. Which acid will produce more H+,
1M HCl or 1M acetic acid?
HCl is strong!
HC2H3COO is weak

11. Recognize the name, formula, and relative strength (weak
or strong) of the following:
Memorize thisWEAK ACIDS
STRONG ACIDS
HCl hydrochloric acid CH3COOH
H2SO4 sulfuric acid aka HC2H3O2 or
HNO3 nitric acid acetic acid (vinegar)
STRONG BASES WEAK BASES
NaOH sodium hydroxide NH3 ammonia
Bronsted-Lowry!
KOH potassium hydroxide
Arrhenius!

12. • A strong acid has a weak conjugate base.
• A weak acid has a strong conjugate base.
• A strong base has a weak conjugate acid.
• A weak base has a strong conjugate acid.

13. Predict the products and label the
conjugate acid-base pairs as weak or
strong.
NH3 + HCl  _______ + _______
CH3COOH + NH3  _______ + _______

14. An acid dissociation constant (Ka)
describes the equilibrium between an
acid and the ions it forms.
HA H+ + A-

15. Weak acids have small Ka values.
The stronger an acid is, the larger is
its Ka value.

16. The base dissociation constant (Kb)
describes the equilibrium of a base.
[HB +][OH-]
Kb = ----------------
[B]
The larger the Kb the more dissociation
occurs, so the stronger the base.