1. 4.10 Relative Strengths of Acids and Bases
Chemistry 12

2. 4.10
In this lesson we will look at the relative strengths of some weak acids and use their Ka values to explain how they would behave when they are combined.

3. 4.10
E.g. 1a) Write the Bronsted-Lowry acid base equilibria for the following reactants. H2PO4- + CO32- ↔
HPO HCO3-
amphiprotic
Can only act as a base

4. 4.10 E.g. 1b) What side is favoured? H2PO4- + CO32- ↔ HPO4 2- + HCO3-
Larger Ka value means that H2PO4- is better at producing H+
products are favored
Ka = 6.2 x10-8
Ka = 5.6 x10-11

5. CO32- is the stronger base
4.10
E.g. 1c)
What is the stronger base?
H2PO4- + CO32- ↔ HPO HCO3-
A stronger acid is ALWAYS on the same side as the stronger base
CO32- is the stronger base

6. 4.10
E.g. 2 a) Using 2 amphiprotic reactants HSO4- + H2PO4- ↔ HINT: Use your B-L table, as the reactant with the larger Ka will behave like an acid.
SO42- + H3PO4

7. 4.10 E.g. 2b) What side is favored? HSO4- + H2PO4- ↔ SO42- + H3PO4
the products are favoured
Ka = 1.2 x10-2
Ka = 7.5 x10-3

8. 4.10 E.g. 2c) Stronger base? HSO4- + H2PO4- ↔ SO42- + H3PO4
Stronger acid
 Stronger base

9. 4.10
E.g. 3) What is the Bronsted-Lowry acid base equilibria that results from the following reactants?
NaHSO4 + NaH2PO4
NaHSO4  Na+ + HSO4-
NaH2PO4  Na+ + H2PO4-
HSO4- + H2PO4- ↔ SO42- + H3PO4
Both reactants dissociate and Na+ is a spectator
These are our reactants
You should notice that this is really the same question as example 2.

10. Learning Check
When given 2 weak acids can you determine which one will act as the acid and which one will act as the base?
Can you identify whether the equilibrium favours the reactants or the products?
Can you do the above with amphiprotic substances? Salts?

11. 4.10
Read & Highlight
Self Notes (p. 6 – 12)
Problems
Hebden # 38-46