Lets walk through them all together:
Atkins and Jones

If 100. mL of a Mg(OH)
2 solution is titrated with 25.0mL of 2.00 M HCl…..
What is the pH at the equivalence point?
How many moles of Mg(OH)
2 were initially present?
What was the concentration of Mg(OH)
2
?

A student weighs 1.823 g of an unknown strong acid into a beaker with
10mL of water. It is titrated to equivalence with 50.0mL of 1.0M NaOH.
What was the molecular mass of the acid.

Acids lose a proton to become the conjugate base.
Acid
Bases gain a proton to become it’s conjugate acid
Conjugate Base
Base Acid
Conjugate
Acid
Conjugate
Base
All acid/base reactions have both an acid and a base in them? So what is the base and conjugate acid in the first reaction? What is the acid and conjugate base in the second reaction?

• Relations between [H + ], [OH ], Kw, pH and pOH pH=7 @25 o C
H
2
O ⇄ H + +OH −
[H + ]=[OH − ]=1x10 -7 @25 o C
K w= [H + ][OH − ]=1x10 -14 @25 o C
Taking the log of both sides:
Can you just memorize this without understanding it?
What happens if the temperature changes?

If water is heated and placed under pressure it has a pH of 6.8. Find the
Kw of water under these conditions. Is it acidic, basic or neutral?
[H + ]=[OH − ] 𝑛𝑒𝑢𝑡𝑟𝑎𝑙
[H + ]=10 −6.8
K w= [H + ][OH − ] k w
=[10 -6.8
] [10 -6.8
]=2.5x10
-14

Weak and Strong Acid and Bases: Compare and Contrast
For strong acids and bases, we assume they completely ionize.
Weak acids and bases ionize to a very limited extent.
Equilibrium lies far to the right
Very Large Ka
Equilibrium lies far to the left
How do I know which is strong and weak?
Memorize the strong, the rest are weak
Very small Ka

What happens to Ka as the strength of the acid increases?
vs https://todaysmeet.com/1CBrindley
The larger the K a the stronger the acid.

What happens to Kb as the strength of the base increases?
If a base is stronger, which way does the equilibrium shift?
It shifts to the right, so what happens to the amount of each product?
So for a stronger base, Kb is higher!!!
https://todaysmeet.com/1CBrindley

HCl
Rank the following solutions in order of increasing acidity. Assume the concentration for each is the same, and that all are within solubility limits.
NaOH NH(CH
3
)
2
NH
2
(CH
3
)
2
+ CH
3
COOH Ca(OH)
2
Strong
Base
Weak
Base
Weak acid
Strong acid

Rank the following solutions in order of increasing acidity. Assume the concentration for each is the same, and that all are within solubility limits.
Strong Weak Weak acid Strong 𝑘 𝑤 Base Base
NH
2
(CH
3
)
2
+ 𝑘 𝑎
=
5.9𝑥10 −4 acid
NaOH NH(CH
3
)
2
= 1.7𝑥10 −11 HCl
Ca(OH)
2
CH
3
COOH
Ka=1.8x10
-5

In what range must the pH of a 0.17M solution of a weak acid fall? pH<7 pH>-log(0.1) pH= 0.77-7
What must be true about the [H+] of a weak acid solution
@25 o C?
Neutral gives [H + ]=[OH ]=10 -7
Acidic has more [H + ] so: >10 -7
What must be true about the [OH-] of a weak acid solution?
Neutral gives [H + ]=[OH ]=10 -7
Acidic has less [OH ] so: <10 -7

Percent Ionization: Pictorial Representation
Original Acid: 14 Dissociated Acid: 3
% ionization= 3/14*100%= 21.4%

I
C
E
Example: The percent dissociation of a 0.800 M aqueous monoprotic weak acid is 0.10%. What is the Ka value for the acid?
HA
0.8 M
0.8-8x10 -4 M
⇄ H
0M
+
8x10 -4 M
+ A −
0M
8x10 -4 M
%𝐷𝑖𝑠𝑠𝑜𝑐𝑖𝑎𝑡𝑖𝑜𝑛 = 𝑑𝑖𝑠𝑠𝑜𝑐𝑖𝑎𝑡𝑒𝑑 𝑎𝑚𝑜𝑢𝑛𝑡
∗ 100% 𝑖𝑛𝑖𝑡𝑖𝑎𝑙 𝑎𝑚𝑜𝑢𝑛𝑡
0.001 = 𝑑𝑖𝑠𝑠𝑜𝑐𝑖𝑎𝑡𝑒𝑑 𝑎𝑚𝑜𝑢𝑛𝑡
0.800 𝑀 𝑑𝑖𝑠𝑠𝑜𝑐𝑖𝑎𝑡𝑒𝑑 𝑎𝑚𝑜𝑢𝑛𝑡 = 8.00𝑥10 −4 𝑀
𝐾 𝑎
=
𝐻
+
𝐻𝐴
𝐴
−
=
8𝑥10
−4
8𝑥10
0.8−8𝑥10 −4
−4
= 8.00x
10 −7

Poly=many
K a1
protic=protons polyprotic=many proton atoms
K=Kw/K a1
K a2
K=Kw/K a2
What is the Kb of CO
3
2?

Molecular Structure and Strength of Acids
Hydrohalic Acids
HX, where X designates a halide (F, Cl, Br, I)
Two competing forces: Enthalpy and Polarity
Enthalpy of HI is much lower than HF, says HI is strongest
Bond polarity would make it seem as if HF should be the strongest
So which wins?
Bond enthalpy weak strong

REMEMBER The more you stabilize the anion, the stronger the acid
Different Central Atoms, Same oxidation number (aka same number of attached groups)
Strength increases with increasing electronegativity of central atom.
Example: HClO
3
>HBrO
3
Same central atom, different number of attached groups
Increases as oxidation number of central atom increases
Example: HClO
4
>HClO
3
>HClO
2
>HClO
+1
<
+3 +5
Oxidation number
Strength of acid
+7

Acid and its conjugate base, or a base and its conjugate acid
Or some combination of components which create this.
(next slide)
It works by converting a strong acid into a weak acid, or a strong base into a weak base.
A strong base can’t exist in solution with a weak acid it must react
A strong acid can’t exist in solution with a weak base it must react

NH
3 and HCl?
Yes!
How: when NH3 and HCl react, they form NH
4
+
I
C
F
NH
3
+ H + → NH
4
+
0.20M
0.10M
0M
0.10M
0.10M
+ 0.10M
0.10M
0M 0.10M
Gives us a conjugate acid base pair

A 100 mL buffer solution is 0.100M Nitrous acid and 0.100M Sodium nitrite. Calculate the pH if a) 0.005 moles of NaOH is added to the solution b) calculate the pH of 0.002 moles of HCl is added to the solution. c) calculate the pH of 0.0150 mols of NaOH is added to the solution. Assume no change in volume.