1. Acids and Bases
Lesson 2
Strong and Weak Bases

2. Review of Bronsted-Lowry Acids

3. FORMING HYDRONIUM IONS
The proton (H+) has been transferred from the HCl molecule to a water molecule. form a hydronium (H3O+) ion and a Cl- ion.   This type of reaction is called ionization (because ions are being formed).
Complete Question 1 on page 4 of your notes.

4. BRONSTED-LOWRY DEFINITION OF ACIDS AND BASES
An acid is any substance which donates (gives) a proton (H+) to another substance.
A base is any substance which accepts (takes) a proton from another substance.
A Bronsted Acid is a proton donor
A Bronsted Base is a proton acceptor

5. BRONSTED-LOWRY DEFINITION OF ACIDS AND BASES
We see that the HCl is donating the proton and the water is accepting the proton.
Therefore HCl is the Bronsted acid and H2O is the Bronsted base.
HCl H2O  H3O Cl-
acid base

6. BRONSTED-LOWRY DEFINITION OF ACIDS AND BASES
Let’s look at another example:
base acid acid base

7. Bronsted Bases Weak Bases acids bases SO32- NH3 CN-
Increasing strength
CO32-
PO43-
Strong Bases- yellow
Oxide O2-
Amide NH2-

8. The two Bronsted strong bases
The two Bronsted strong bases. They are found on the right bottom area of the acid chart pg. 485 H+
O2-
H2O
OH-
OH- H+
NH2-
H2O
NH3
OH-
Again, all bases make OH-
® means strong

9. Bronsted Weak Bases H+ F- + H2O ⇄ HF + OH- H+ C2O42- + H2O ⇄ HC2O4-

10. Arrhenius bases

11. Arrhenius Bases Strong Bases- yellow LiOH NaOH KOH RbOH CsOH FrOH
Ra(OH)2
Sr(OH)2
Ba(OH)2

12. Weak Bases-
most other metals
Arrhenius Bases
Be(OH)2
Zn(OH)2
AgOH

13. Strong Bases Strong bases completely ionize in water to produce OH-
There are 11 Arrhenius strong bases - Group I and Group II hydroxides
LiOH ® Li+ + OH-
KOH ® K+ + OH-
Sr(OH)2 ® Sr2+ + 2OH-
Ra(OH)2 ® Ra2+ + 2OH-
® means strong
Note all bases make OH-

14. Arrhenius Weak Bases
A weak base is one that partially reacts with water to produce OH-.
Be(OH)2(s) ⇄ Be2+ + 2OH-
Zn(OH)2(s) ⇄ Zn2+ + 2OH-

15. H+
C6H5O73-
+ H2O ⇄
HC6H5O72-
OH- H+
NH3
+ H2O ⇄
NH4+
OH-
Whether you consider Arrhenius or Bronsted-Lowry, BASES act the same way: They all make OH- by accepting a proton from water!

16. Weak bases
At equilibrium, use
Use Kb
Base ionization constant

17. Write the Kb expression for the following 3 weak bases
[HF][OH-]
Kb =
[F-]
[HC2O4-][OH-]
Kb =
[C2O42-]
[H2CO3][OH-]
Kb =
[HCO3-]

18. AMPHIPROTIC SUBSTANCES
Some substances (ex: H2O) are capable of acting as an ACID (when surrounded by a stronger base) OR acting as a BASE (when surrounded by a stronger acid).
Substances that act as acids or bases are called amphiprotic.

19. AMPHIPROTIC SUBSTANCES
Other amphiprotic substances:
H2O
H2PO4-
HCO3-
+ H H+
Example: H3PO H2PO HPO42-

20. AMPHIPROTIC SUBSTANCES
In general, amphiprotic substances…
Have a negative charge and
An easily removable hydrogen.

21. AMPHIPROTIC SUBSTANCES
Identify the acid and base in the reactants of the following reactions:
H2S + HCO3-  H2CO3 + HS-
NH H2O  H3O NH3
HCOOH + HSO3-  H2SO3 + HCOO-

22. CONJUGATE ACID-BASE PAIRS
Conjugate acid – the species with one more proton (ex. HIO3)
Conjugate base - the species with one less proton (ex. IO3- )
*There will always be 2 conjugate pairs

23. POLYPROTIC ACIDS
The formula of an acid tells us how many protons (H+) the acid can donate.
An acid that can supply:
ONE proton (ex: HCl) = monoprotic acid
TWO protons (ex: H2SO4) = diprotic acid
THREE protons (ex: H3PO4) = triprotic acid
More than ONE proton = polyprotic acid

24. Write the acid base equilibria when this pair is mixed;
HCN and F-