1. Acids and Bases

2. An Acid is a substance that can release a proton or hydrogen ion (H+ )when dissolved in water”
HCl H+ + Cl- .
A base is a substance that accepts a proton .

3. A base can be defined as a substance that can release OH- ions when dissolved in water . NaOH OH- + Na+ .
“ A Base is a substance that can release a
Hydroxyl ion when dissolved in water”

4. Example of conjugate acid – base pairs CH3COOH / CH3COO- H2CO3 / HCO3-

9. Weak acids and aeak bases

10. Weak acids .
Weak acids and bases dissociate weakly in solutions thus they are predominantly present in the molecular form.
Dissociation of weak acids Ka;
In aqueous solutions weak acids ionize to a very limited extent as follows;
HA + H2O H3O+ + A-
Ki = [H3O+ ] [A- ]
[H2O][HA]
Since [H2O] is constant a new constant ka can be introduced ,
ka = [H3O+ ] [A- ]
[HA]

11. Dissociation of water
Water molecules can dissociate in water as follows,
H2O H + + OH-
The tendency of water to ionize is expressed as Ki
Ki = [ H + ] [OH- ]
[ H2O]
Calculation of Ki ;
Since 1 mole of H2O weighs 18g , thus the number of molecules in 1l of water (1000g)
No of moles of water in 1 l = wt / MWt = 1000/ 18 = 55.56mole
So the molarity of pure water is 55.5M.
Since the probability that a hydrogen is present as an ion is 1.8 x10-9
thus the Molar concentration of both [ H + ] and [OH- ] can be
calculated as 1.8 x x = 1.0 x M .
Thus Ki = [ H + ] [OH- ] = x = x M .
[ H2O]

12. Ionization of water To calculate for kw ; Ki = [ H + ] [OH- ] [ H2O]
Ki [ H2O] = [ H + ] [OH- ]
1.8 x x = 1x = [ H + ] [OH- ]
So kw = [ H + ]+ [OH- ] = 1x10-14
Taking -log of both sides
-log kw = -log [ H + ] -log[OH- ]
p kw = p [ H + ] + p[OH- ] = = 14