1. 4.6 Acids and Bases: General Principles1

2. 4.6 Acids and Bases: General Principles
Brønsted-Lowry definition an acid is a proton donor a base is a proton acceptor 1

3. Proton Transfer from HBr to Water
hydronium ion H Br O . – .. +
base acid conjugate conjugate acid base 2

4. A strong acid is one that is completely ionized in water.
Acid Strength
A strong acid is one that is completely ionized in water.
A weak acid is one that ionizes in water to the extent of less than 100%.
Acid strength is measured by Ka or pKa 3

5. Equilibrium constant for proton transferH . H . .. + Br – . .. . . . O + H Br O H + ..
[H3O+][Br–]
K =
[HBr]
[H+][Br–]
K a =
[HBr]
pK a = – log Ka 4

6. Table 4.2 Strength of Some Brønsted AcidsK a p C on j . B se H I ~ 1 10 – HB r 9
HCl 7 Cl 2 S O 4 1. 6
x 1 5 .8 HS 3 + .5 .7
strong acids are stronger than hydronium ion 5

7. Table 4.2 Strength of Some Brønsted AcidsK a p C on j . B se H 3 O + 5 .5 – 1 .7 2 F 3.
x 1 –4 CH 1. 8 –5 4. 6 NH 4 5.
–10 9.
–16
weak acids are weaker than hydronium ion 5

8. Table 4.2 Strength of Some Brønsted AcidsK a p C on j . B se H 2 O 1. 8
x 1 - 16 1 5 .7 – CH 3 ~ 6 ( ) 17 7 18
alcohols resemble water in acidity; their conjugate bases are comparable to hydroxide ion in basicity 5

9. Table 4.2 Strength of Some Brønsted AcidsK a p C on j . B se NH 3 ~ 1 - 36 6 2 – ( CH ) N
ammonia and amines are very weak acids; their conjugate bases are very strong bases 5

10. Proton Transfer to Alcohols
alkyloxonium ion H Br O R . – .. +
base acid conjugate conjugate acid base 2

11. 4.7 Acid-Base Reactions: A Mechanism for Proton Transfer1

12. Proton Transfer from HBr to Water. – .. +
base acid conjugate conjugate acid base 2

13. Mechanism: single step
transition state
Potential energy
activation energy
reactants
products
Reaction coordinate 22

14. Mechanism: single stepd+ d-
H2O H Br
bimolecular: both H2O and HBr involved at transition state
Potential energy
H2O + H—Br
H2O—H + Br – +
Reaction coordinate 22