1. Do Now:
NCEA Equilibrium Q.

2. Acids and Bases
Chemistry 201

3. Kaupapa / Learning Outcome
At the end of todays lesson I will be able to define what an acid and base are using Bronsted-Lowry definitions and write equations to show the nature of acids and bases in terms of proton transfer. This includes ionic species such as NH4+, CH3COO- etc.

5. Acid-Base Reactions in Solution: Crash Course Chemistry #8

6. Acids
Acids were originally classified in terms of the following behaviour in aqueous solution:
acids turn blue litmus red
acids have a pH less than 7
acids neutralise bases
acids react with metal carbonates which fizzes and produces CO2 gas.
acids react with active metals to produce hydrogen gas (but not with Cu, Ag or Au).
acids taste sour.

7. Bases In contrast, aqueous solutions of bases turn red litmus blue,
have a pH greater than 7,
neutralise acids,
taste bitter,
feel soapy

8. Bronsted-Lowry
Acids are classified as those substances that donate a proton (H+). Similarly bases are proton acceptors.

9. Bronsted-Lowry Acids HA(aq) + H2O(l) → H3O+(aq) + A (aq)
Proton (H+) donation
HA(aq) H2O(l) → H3O+(aq) A (aq)
proton donor
proton acceptor
HA is the acid and H2O is the base in this reaction
Acids donate protons to water to form the hydronium ions (H3O+)

10. Bronsted-Lowry Bases H2O(l) + B(aq) → OH-(aq) + BH+(aq)
Proton (H+) donation
H2O(l) B(aq) → OH-(aq) BH+(aq)
proton donor
proton acceptor
B is the base and H2O is the acid in this reaction
Bases accept protons from water to form the hydroxide ions (OH-)

11. Amphiprotic Substance
Amphiprotic substances can accept and donate protons (behave as acids and bases). Eg. HCO3-
Acid: HCO3- (aq) + OH-(aq) ↔ CO32-(aq) + H2O(l)
Base: HCO3-(aq) + H3O+(aq) ↔ H2CO3(aq) + H2O(l)
HCO3- donates a proton
HCO3- accepts a proton

12. Remember water can act as an acid by donating an H+ or a base by accepting an H+

13. Conjugate Acids & Bases
If two species differ by just one proton they are classed as a conjugate acid-base pair.
H2O(l) B(aq) ↔ BH+(aq) OH(aq)
acid base acid 2 base 1
The conjugate acid/base pairs in the above reaction are:
Acid Base
H2O / OH-
BH+ / B

14. Exercises 1. Complete the acid/base pairs for each of the following:
acids - H2CO3 HSO4 H2O HCl
(b) bases - HSO4 SO42 H2O CH3COO
2. Which of the species listed above can be classified as amphiprotic?
bases - HCO SO OH Cl -
acids - H2SO HSO H3O CH3COOH